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Windows Control: The Tree View

 

Tree View Fundamentals

 

Introduction

A tree view is a control that resembles an upside down tree and displays a hierarchical list of items. Like a normal tree, a tree view starts in the top section with an object referred to as the root. Under the root, a real tree is made of branches and leaves. In an application, a tree view is only made of branches and each branch is called a node. In real world, a leaf cannot have a branch as its child, only a branch can have another branch as its child and a branch can have a leaf as a child. In an application, a node (any node) can have a node as a child.

   

Tree

 

Like a real world tree, the branches or nodes of a tree view use a type of relationship so that they are not completely independent. For example, a tree view can be based on a list that has a parent item and other child items that depend on that parent. In real world, if you cut a branch, the branches and leaves attached to it also disappear. This scenario is also valid for a tree view.

Most of the time, a tree has only one root but a tree in an application can have more than one root.

Tree
 

Tree View Creation

In a Windows application a tree view is primarily a control like any other. To use it in your application, you can click the TreeView button in the Toolbox and click a form or other control in your application. This is equivalent to programmatically declaring a variable of type TreeView, using the new operator to instantiate it and adding it to its container's list of controls through a call to the Controls.Add() method. Here is an example:

Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class Starter
        Inherits Form

        Private tvwCountries As TreeView

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()

            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Controls.Add(tvwCountries)
        End Sub

    End Class

    Function Main() As Integer

        Dim frmStart As Starter = New Starter

        Application.Run(frmStart)

        Return 0
    End Function

End Module

This would produce:

Countries Statistics

Using a TreeView variable only adds a rectangular empty control to your application. The next action you probably take is to add one or more branches to the tree.

Practical LearningPractical Learning: Introducing the Tree View Control

  1. Start Microsoft Visual Basic
  2. Create a new Windows Application named CollegeParkAutoParts2
  3. In the Solution Explorer, right-click Form1.vb and click Rename
  4. Type Central.vb and press Enter
  5. From the Containers section of the Toolbox, click Panel and click the form
  6. Set its Dock property to Top
  7. From the Containers section of the Toolbox, click Panel and click the form
  8. Set its Dock property to Bottom
  9. From the Containers section of the Toolbox, click SplitContainer and click the middle of the form
  10. Design the form as follows:
     
    College Park Auto Parts - Form Design
    Control Text Name Other Properties
    Label Label College Park Auto-Parts   BorderStyle: FixedSingle
    Font: Times New Roman, 20.25pt, style=Bold
    AutoSize: False
    TextAlign: MiddleCenter
    GroupBox     Anchor: Top, Bottom, Left, Right
    TreeView TreeView   tvwAutoParts Anchor: Top, Bottom, Left, Right
    GroupBox GroupBox     Anchor: Top, Bottom, Left, Right
    ListView ListView   lvwAutoParts View: Details
    Anchor: Top, Bottom, Left, Right
    Columns   (Name) Text TextAlign Width
    colPartNumber Part #    
    colPartName Part Name   300
    colUnitPrice Unit Price Right 80
    GroupBox GroupBox Selected Parts    
    Label Label Part #   Anchor: Bottom, Left
    Label Label Part Name   Anchor: Bottom, Left, Right
    Label Label Unit Price   Anchor: Bottom, Right
    Label Label Qty   Anchor: Bottom, Right
    Label Label Sub Total   Anchor: Bottom, Right
    TextBox TextBox   txtPartNumber1 Anchor: Bottom, Left
    TextBox TextBox   txtPartName1 Anchor: Bottom, Left, Right
    TextBox TextBox 0.00 txtUnitPrice1 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0 txtQuantity1 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0.00 txtSubTotal1 TextAlign: Right
    Anchor: Bottom, Right
    Button Button Remove btnRemove1 Anchor: Bottom, Right
    TextBox TextBox   txtPartNumber2 Anchor: Bottom, Left
    TextBox TextBox   txtPartName2 Anchor: Bottom, Left, Right
    TextBox TextBox 0.00 txtUnitPrice2 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0 txtQuantity2 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0.00 txtSubTotal2 TextAlign: Right
    Anchor: Bottom, Right
    Button Button Remove btnRemove2 Anchor: Bottom, Right
    TextBox TextBox   txtPartNumber3 Anchor: Bottom, Left
    TextBox TextBox   txtPartName3 Anchor: Bottom, Left, Right
    TextBox TextBox 0.00 txtUnitPrice3 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0 txtQuantity3 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0.00 txtSubTotal3 TextAlign: Right
    Anchor: Bottom, Right
    Button Button Remove btnRemove3 Anchor: Bottom, Right
    TextBox TextBox   txtPartNumber4 Anchor: Bottom, Left
    TextBox TextBox   txtPartName4 Anchor: Bottom, Left, Right
    TextBox TextBox 0.00 txtUnitPrice4 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0 txtQuantity4 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0.00 txtSubTotal4 TextAlign: Right
    Anchor: Bottom, Right
    Button Button Remove btnRemove4 Anchor: Bottom, Right
    TextBox TextBox   txtPartNumber5 Anchor: Bottom, Left
    TextBox TextBox   txtPartName5 Anchor: Bottom, Left, Right
    TextBox TextBox 0.00 txtUnitPrice5 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0 txtQuantity5 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0.00 txtSubTotal5 TextAlign: Right
    Anchor: Bottom, Right
    Button Button Remove btnRemove5 Anchor: Bottom, Right
    TextBox TextBox   txtPartNumber6 Anchor: Bottom, Left
    TextBox TextBox   txtPartName6 Anchor: Bottom, Left, Right
    TextBox TextBox 0.00 txtUnitPrice6 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0 txtQuantity6 TextAlign: Right
    Anchor: Bottom, Right
    TextBox TextBox 0.00 txtSubTotal6 TextAlign: Right
    Anchor: Bottom, Right
    Button Button Remove btnRemove6 Anchor: Bottom, Right
    GroupBox GroupBox Order Summary   Anchor: Top, Bottom, Left, Right
    Label Label Total Order:   Anchor: Bottom, Right
    TextBox TextBox 0.00 txtTotalOrder Anchor: Bottom, Right
    Button Button Close btnClose Anchor: Bottom, Right
  11. Execute the application to test it
  12. Close the form and return to your programming environment

Introduction to Creating Tree View Nodes

 

Visually Creating Nodes

To create the nodes of a tree view, Microsoft Visual Studio provides a convenient dialog box you can use at design time. To display it, after adding a tree view control to a form, you can click the ellipsis button of its Nodes field in the Properties window. This would open the TreeNode Editor:

Tree Node Editor

The primary characteristic of a node is the text it displays. At design time and in the TreeNode Editor, to create a node, you can click the Add Root button. When you do this, a node with a default but incremental name is created. To edit a node's name, first select it in the Select Node To Edit list, then, on the right side, click Name and enter the string you wish.

Programmatically Creating Nodes

The branches of a tree view are stored in a property called Nodes. The Nodes property is an object based on the TreeNodeCollection class. The TreeNodeCollection class implements the IList, the ICollection, and the IEnumerable interfaces.

As its name indicates, the Nodes property carries all of the branches of a tree view. This means that the Nodes property in fact represents a collection. Each member of this collection is called a node and it is an object based on the TreeNode class.

At run time, to create a new node, call the TreeNodeCollection.Add() method which is overloaded with two versions. One of the versions of this method uses the following syntax:

Public Overridable Function Add(text As String) As TreeNode

This method takes as argument the string that the branch will display. This method is also the prime candidate to create a root node. Here is an example of calling it:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.Nodes.Add("World")

            Controls.Add(tvwCountries)
End Sub

This would produce:

Countries Statistics

Practical LearningPractical Learning: Creating the Root Node

  1. Right-click the form and click View Code
  2. In the Class Name combo box, select (Central Events)
  3. In the Method Name combo box, select Load and implement the event as follows:
    Private Sub CentralLoad(ByVal sender As Object, 
                                 ByVal e As System.EventArgs) 
                                 Handles Me.Load
        Dim nodRoot As TreeNode = 
    	tvwAutoParts.Nodes.Add("College Park Auto-Parts")
    
        For i As Integer = Date.Today.Year To 1960 Step -1
                nodRoot.Nodes.Add(i)
        Next
    End Sub
  4. Execute the application to test the form
     
    College Park Auto-Parts
  5. Close the form and return to your programming environment
  6. On the main menu, click Project -> Add Class...
  7. Set the name to PartDescription and press Enter
  8. To create a class that can holds a structured item of a list, change the class as follows:
    Public Class PartDescription
        ' These members will be used to define a car part
        Private ID As Long
        Private yr As Integer
        Private mk As String
        Private mdl As String
        Private cat As String
        Private name As String
        Private price As Double
    
        Public Sub New()
            ID = 0
            yr = 1960
            mk = ""
            mdl = ""
            name = "Unknown"
            price = 0.0
        End Sub
    
        Public Sub New(ByVal code As Long, ByVal year As Integer, 
                       ByVal make As String, ByVal model As String, 
                       ByVal type As String, ByVal desc As String, 
                       ByVal UPrice As Double)
            ID = code
            yr = year
            mk = make
            mdl = model
            cat = type
            name = desc
            price = UPrice
        End Sub
    
        Public Property PartNumber() As Long
            Get
                Return ID
            End Get
            Set(ByVal value As Long)
                ID = value
            End Set
        End Property
    
        Public Property CarYear() As Integer
            Get
                Return yr
            End Get
            Set(ByVal value As Integer)
                yr = value
            End Set
        End Property
    
        Public Property Make() As String
            Get
                Return mk
            End Get
            Set(ByVal value As String)
                mk = value
            End Set
        End Property
    
        Public Property Model() As String
            Get
                Return mdl
            End Get
            Set(ByVal value As String)
                mdl = value
            End Set
        End Property
    
        Public Property Category() As String
            Get
                Return cat
            End Get
            Set(ByVal value As String)
                cat = value
            End Set
        End Property
    
        Public Property PartName() As String
            Get
                Return name
            End Get
            Set(ByVal value As String)
                name = value
            End Set
        End Property
    
        Public Property UnitPrice() As Double
            Get
                Return price
            End Get
            Set(ByVal value As Double)
                price = value
            End Set
        End Property
    
        Public Overrides Function ToString() As String
            Return PartNumber & " " & 
                       CarYear.ToString() & " " & 
                       Make & " " & 
                       Model & " " & 
                       Category & " " & 
                       PartName & " " & 
                       UnitPrice
        End Function
    End Class
 

A Node and its Children

 

Introduction

The other version of the TreeNodeCollection.Add() method uses the following syntax:

Public Overridable Function Add(node As TreeNode) As Integer

This method takes as argument a TreeNode object. In other words, it expects a complete or semi-complete branch already defined somehow.

The TreeNode class is equipped with various constructors you can use to instantiate it. Its default constructor allows you to create a node without primarily giving its details. Another TreeNode constructor has the following syntax:

Public Sub New(text As String)

This constructor takes as argument the string that the node will display. Here is an example of using it and adding its newly create node to the tree view:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodElement As TreeNode = New TreeNode("World")
            tvwCountries.Nodes.Add(nodElement)

            Controls.Add(tvwCountries)
End Sub

We mentioned that the primary characteristic of a node is the text it displays. The text of a node is stored in a property of the TreeNode class and is called Text. This allows you either to specify the string of a node or to retrieve it when needed. Here is an example of setting it:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodElement As TreeNode = New TreeNode
            nodElement.Text = "World"
            tvwCountries.Nodes.Add(nodElement)

            Controls.Add(tvwCountries)
End Sub

Just as we called the TreeNodeCollection.Add() method to create a branch, you can call it as many times as necessary to create additional branches. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.Nodes.Add("World")
            tvwCountries.Nodes.Add("Jupiter")
            tvwCountries.Nodes.Add("Neptune")
            tvwCountries.Nodes.Add("Uranus")

            Controls.Add(tvwCountries)
End Sub

This would produce:

Countries Statistics

Alternatively, if you have many branches to add to the tree, you can first create them as an array of TreeNode values, then called the TreeNodeCollection.AddRange() method. The syntax of this method is:

public virtual void AddRange(TreeNode() nodes)

This method takes as argument an array of TreeNode objects. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodPlanets() As TreeNode = 
            { 
                New TreeNode("World"), 
                New TreeNode("Jupiter"), 
                New TreeNode("Neptune"), 
                New TreeNode("Uranus") 
            }
            tvwCountries.Nodes.AddRange(nodPlanets)

            Controls.Add(tvwCountries)
End Sub

Creating Child Nodes

At design time and in the TreeNode Editor, to create a child node for an existing item, first select it in the Select Node To Edit list, then click the Add Child button. This causes a child node to be created for the selected item. To edit its name, first click it and change the string in the Label text box.

At run time, to create a child node, first get a reference to the node that will be used as its parent. One way you can get this reference is to obtain the returned value of the first version of the TreeNodeCollection.Add() method. As its syntax indicates, this method returns a TreeNode object.

We have used the default constructor of the TreeNode class and the constructor that takes as argument a string. The TreeNode class provides another constructor whose syntax is:

Public Sub New(text As String, children As TreeNode())

The first argument of this method is the string that the new node this constructor creates will display. The second argument is a collection of the child nodes of this branch. The collection is passed as an array. Based on this, you use this constructor to create a new node including its children. After creating the new node, you can pass it to the TreeNodeCollection.Add() method as we did earlier. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodContinents() As TreeNode = 
            { 
                New TreeNode("Africa"), 
                New TreeNode("America"), 
                New TreeNode("Asia"), 
                New TreeNode("Europe") 
            }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            Controls.Add(tvwCountries)
End Sub

This would produce

Countries Statistics

Using the same approach, you can create as many branches and their child nodes as you wish. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            ' Create a list of some African countries and 
            ' store them in an array named nodAfricans
            Dim nodAfricans() As TreeNode = 
            { 
                New TreeNode("Senegal"), 
                New TreeNode("Botswana"), 
                New TreeNode("Ghana"), 
                New TreeNode("Morocco") 
            }

            ' Create a list of some American countries and 
            ' store them in an array named nodAmericans
            Dim nodAmericans() As TreeNode = 
            { 
                New TreeNode("Canada"), 
                New TreeNode("Jamaica"), 
                New TreeNode("Colombia") 
            }

            ' Create a list of some European countries and 
            ' store them in an array named nodEuropeans
            Dim nodEuropeans() As TreeNode = 
            { 
                New TreeNode("Italy"), 
                New TreeNode("Greece"), 
                New TreeNode("Spain"), 
                New TreeNode("England") 
            }

            ' Create a list of continents, independently
            Dim nodAfrica As TreeNode = New TreeNode("Africa", nodAfricans)
            Dim nodAmerica As TreeNode = New TreeNode("America", nodAmericans)
            Dim nodAsia As TreeNode = New TreeNode("Asia")
            Dim nodEurope As TreeNode = New TreeNode("Europe", nodEuropeans)

            ' Store the list of continents in an array named nodContinents
            Dim nodContinents() As TreeNode = 
            {nodAfrica, nodAmerica, nodAsia, nodEurope}

            ' Create a branch named nodWorld and store the list of
            ' continents as its child
            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)

            ' Finally, add the nodWorld branch to the tree view
            tvwCountries.Nodes.Add(nodWorld)

            Controls.Add(tvwCountries)
End Sub

This would produce:

Countries Statistics

Practical LearningPractical Learning: Creating Child Nodes

  1. Access the Central.vb code file and change it as follows:
    Private parts(55) As PartDescription
    
    Private Sub CentralLoad(ByVal sender As Object, 
                                 ByVal e As System.EventArgs) 
                                 Handles Me.Load
      Dim nodRoot As TreeNode = tvwAutoParts.Nodes.Add("College Park Auto-Parts")
    
            ' This is simply used to initialize the whole array with empty parts
            ' This is just to make sure that each member of the array is defined
            For i As Integer = Date.Today.Year To 1960 Step -1
                nodRoot.Nodes.Add(i)
            Next
    
            parts(0) = New PartDescription(447093, 2002, "Ford", 
                "Escort SE L4 2.0", "Engine Electrical", 
                "Alternator 75amp  Remanufactured; w/ 75 Amp", 
                205.05)
            parts(1) = New PartDescription(203815, 2006, "Dodge", 
                "Caravan SE L4 2.4", "Cooling System", 
                "Radiator Cap", 6.65)
            parts(2) = New PartDescription(293047, 2000, "Toyota", 
                "RAV4 2WD/4-DOOR", "Cooling System", 
                "Thermostat Gasket", 4.95)
            parts(3) = New PartDescription(990468, 2002, "Honda", 
                "Civic 1.7 EX 4DR", "Exhaust", 
                "Bolt & Spring Kit (Manifold outlet, Muffler Inlet)", 
                85.75)
            parts(4) = New PartDescription(304158, 1996, "Buick", 
                "Regal Custom V6 3.8", "Fuel Injection", 
                "Fuel Injector", 82.75)
            parts(5) = New PartDescription(807245, 2004, "Acura", 
                "MDX 3.5 4WD", "Driveshaft & Axle", 
                "CV Boot Clamp 7 x 750mm; 1 Large + 1 Small Clamp", 
                1.6)
            parts(6) = New PartDescription(203485, 2001, "Ford", 
                "Taurus LX V6 3.0", "Fuel Injection", 
                "Oxygen Sensor OE Style 4Wire; Front; 2 Required", 
                52.65)
            parts(7) = New PartDescription(248759, 1999, "Jeep", 
                "Wrangler Sahara", "Air Intake", 
                "Air Filter AirSoft Panel", 7.95)
            parts(8) = New PartDescription(202848, 1998, "Honda", 
                "Accord 2.3 LX 4DR", "Air Intake", 
                "Air Filter", 12.55)
            parts(10) = New PartDescription(932759, 2006, "Kia", 
                "Rio 1.6DOHC16V 4-DR", "Cooling System", 
                "Thermostat", 14.45)
            parts(11) = New PartDescription(304975, 2000, "Honda", 
                "Civic 1.6 EX 4DR", "Suspension", 
                "Ball Joint; Front Lower; 2 per car", 40.55)
            parts(12) = New PartDescription(208450, 2003, "Chevrolet", 
                "Monte Carlo LS V6 3.4", "Fuel Injection", 
                "Oxygen Sensor OE connector; Rear", 65.55)
            parts(13) = New PartDescription(209480, 2002, "Ford", 
                "Focus SE DOHC L4 2.0", "Steering", 
                "Steering Rack Remanufactured", 170.85)
            parts(9) = New PartDescription(203495, 2004, "Honda", 
                "Civic 1.7 EX 4DR", "Climate Control", 
                "A/C Clutch; OE compressor = Sanden", 184.95)
            parts(14) = New PartDescription(203480, 2007, "Toyota", 
                "Corolla", "Air Intake", 
                "Air Filter", 12.65)
            parts(15) = New PartDescription(109379, 2005, "Volvo", 
                "S40 2.5L T5 AWD", "Fuel Delivery", 
                "Fuel Filter; Early Design; Outer Diameter = 55mm", 
                30.95)
            parts(16) = New PartDescription(935794, 2002, "Ford", 
                "Escape XLS 4WD", "Brake", 
                "Brake Caliper Remanufactured; Front Right", 
                65.55)
            parts(17) = New PartDescription(203485, 2006, "BMW", 
                "325i", "Climate Control", 
                "AC High Pressure Side Switch", 
                49.95)
            parts(18) = New PartDescription(204875, 1996, "Chevrolet", 
                "Monte Carlo Z34 V6 3.4", "Fuel Delivery", 
                "Fuel Filter", 8.05)
            parts(19) = New PartDescription(937485, 2007, "Toyota", 
                "Camry V6", "Air Intake", "Air Filter", 12.95)
            parts(20) = New PartDescription(294759, 2001, "Ford", 
                "Escape XLT 4WD", "Air Intake", 
                "Air Filter Panel", 7.25)
            parts(21) = New PartDescription(297495, 2003, "Honda", 
                "Civic 1.7 EX 4DR", "Brake", 
                "Brake Caliper Reman; w/ ProAct Pads; Front Right", 
                82.55)
            parts(22) = New PartDescription(794735, 2006, "BMW", 
                "325i", "Climate Control", 
                "Cabin Air/Pollen Filter; With Activated Carbon", 
                28.05)
            parts(23) = New PartDescription(937485, 2007, "Toyota", 
                "Corolla", "Body Electrical", 
                "Halogen  SilverStar; 12V 65W; inner-high beam", 
                22.85)
            parts(24) = New PartDescription(492745, 2005, "Ford", 
                "Focus ZX3 L4 2.0", "Air Intake", 
                "Fuel Injection Perf Kit", 342.95)
            parts(25) = New PartDescription(937005, 2004, "Acura", 
                "MDX 3.5 4WD", "Driveshaft & Axle", 
                "CV Boot Clamp 7 x 750mm; For Large End of Boot; inner boot", 
                1.6)
            parts(26) = New PartDescription(293749, 2004, "Acura", 
                "MDX 3.5 4WD", "Driveshaft & Axle", 
                "Axle Nut 24mm x 1;5; rear ", 2.35)
            parts(27) = New PartDescription(920495, 2006, "BMW", 
                    "325i", "Climate Control", 
                    "Adjustable Telescoping Mirror", 7.95)
            parts(28) = New PartDescription(204075, 2004, "Acura", 
                "MDX 3.5 4WD", "Driveshaft & Axle", 
                "Wheel Bearing; Rear; 1 per wheel", 70.15)
            parts(29) = New PartDescription(979304, 2000, "Toyota", 
                "RAV4 2WD/4-DOOR", "Cooling System", 
                "Thermostat Housing", 20.95)
            parts(30) = New PartDescription(300456, 2004, "Acura", 
                "MDX 3.5 4WD", "Driveshaft & Axle", 
                "Wheel Bearing; Front; 1 per wheel", 
                66.65)
            parts(31) = New PartDescription(404860, 2001, "Ford", 
                "Taurus LX V6 3.0", "Suspension", 
                "Shock Absorber GR2; Rear; Wagon only", 
                39.4)
            parts(32) = New PartDescription(585688, 2007, "Buick", 
                "Lacrosse CXS V6 3.6", "Brake", 
                "Climate Control", 10.65)
            parts(33) = New PartDescription(739759, 2001, "Ford", 
                "Taurus LX V6 3.0", "Suspension", 
                "Shock Absorber GasaJust; Rear; Wagon only", 
                30.95)
            parts(34) = New PartDescription(927495, 2005, "Volvo", 
                "S40 2.5L T5 AWD", "Engine Mechanical", 
                "Timing Belt Idler Pulley Original Equipment INA", 
                65.55)
            parts(40) = New PartDescription(979374, 2000, "Toyota", 
                "RAV4 2WD/4-DOOR", "Cooling System", 
                "Thermostat Gasket", 4.95)
            parts(35) = New PartDescription(542347, 2007, "Buick", 
                "Lacrosse CXS V6 3.6", "Brake", 
                "Brake Pad Set ProACT Ceramic w/Shims; Front", 80.05)
            parts(36) = New PartDescription(683064, 2000, "Toyota", 
                "RAV4 2WD/4-DOOR", "Cooling System", 
                "Radiator Hose; Upper", 103.75)
            parts(37) = New PartDescription(248759, 1999, "Jeep", 
                "Wrangler Sahara", "Air Intake", 
                "Air Filter", 50.95)
            parts(38) = New PartDescription(973974, 2007, "Toyota", 
                "Corolla", "Air Intake", 
                "Air Mass Meter; W/o Housing; Meter/sensor only", 
                134.95)
            parts(39) = New PartDescription(285800, 2001, "Ford", 
                "Escape XLT 4WD", "Transmission", 
                "AT Filter", 34.95)
            parts(41) = New PartDescription(207495, 2007, "Toyota", 
                "Corolla", "Body Electrical", 
                "Headlight Bulb; 12V 65W; inner-high beam", 9.35)
            parts(42) = New PartDescription(566676, 2000, "Toyota", 
                "RAV4 2WD/4-DOOR", "Cooling System", 
                "Auxiliary Fan Switch", 42.95)
            parts(43) = New PartDescription(304950, 2007, "Toyota", 
                "Corolla", "Body Electrical", 
                "Headlight Bulb; 12V 51W; outer", 7.85)
            parts(44) = New PartDescription(797394, 2000, "Toyota", 
                "RAV4 2WD/4-DOOR", "Cooling System", 
                "Water Flange Gasket", 0.85)
            parts(45) = New PartDescription(910203, 2007, "Buick", 
                "Lacrosse CXS V6 3.6", "Suspension", 
                "Strut Mount Inc; Sleeve; Rear Right", 80.85)
            parts(46) = New PartDescription(790794, 2000, "Toyota", 
                "RAV4 2WD/4-DOOR", "Cooling System", 
                "Radiator Hose; Lower", 9.45)
            parts(47) = New PartDescription(970394, 2007, "Buick", 
                "Lacrosse CXS V6 3.6", "Suspension", 
                "Coil Spring Insulator; Front Lower", 14.55)
            parts(48) = New PartDescription(290840, 2005, "Volvo", 
                "S40 2.5L T5 AWD", "Engine Mechanical", 
                "Rod Bearing Set 1 per Rod; Standard; Reqs. 5-per Engine", 
                26.95)
            parts(49) = New PartDescription(209704, 2007, "Toyota", 
                "Corolla", "Body Electrical", 
                "Wiper Blade Excel+; Front Right", 7.25)
            parts(50) = New PartDescription(200368, 2000, "Toyota", 
                "RAV4 2WD/4-DOOR", "Cooling System", 
                "Radiator Drain Plug incl; gasket", 3.15)
            parts(51) = New PartDescription(200970, 2005, "Volvo", 
                "S40 2.5L T5 AWD", "Engine Mechanical", 
                "Reference Sensor; Flywheel Engine Speed", 
                62.05)
            parts(52) = New PartDescription(542347, 2007, "Buick", 
                "Lacrosse CXS V6 3.6", "Air Intake", 
                "Air Filter", 50.25)
            parts(53) = New PartDescription(927045, 2001, "Ford", 
                "Escape XLT 4WD", "Air Intake", 
                "Air Filter", 62.95)
            parts(54) = New PartDescription(990659, 2000, "Toyota", 
                "RAV4 2WD/4-DOOR", "Cooling System", 
                "Radiator OE Plastic tank", 136.85)
            parts(55) = New PartDescription(440574, 2007, "Buick", 
                "Lacrosse CXS V6 3.6", "Suspension", 
                "Strut Mount Inc; Sleeve; Rear Left", 
                80.8)
    
            ' Showing the makes nodes
    
            ' Showing the makes nodes
            For Each nodYear As TreeNode In nodRoot.Nodes
    
                Dim lstMakes As ArrayList = New ArrayList()
    
                For Each part As PartDescription In parts
    
                    If nodYear.Text = part.CarYear.ToString() Then
                        If Not lstMakes.Contains(part.Make) Then
                            lstMakes.Add(part.Make)
                        End If
                    End If
    
                Next
    
                For Each strMake As String In lstMakes
                    nodYear.Nodes.Add(strMake)
                Next
            Next
    
            ' Showing the models nodes
            For Each nodYear As TreeNode In nodRoot.Nodes
                For Each nodMake As TreeNode In nodYear.Nodes
    
                    Dim lstModels As ArrayList = New ArrayList()
    
                    For Each part As PartDescription In parts
    
                        If nodYear.Text = part.CarYear.ToString() And 
                            (nodMake.Text = part.Make) Then
    
                            If Not lstModels.Contains(part.Model) Then
                                lstModels.Add(part.Model)
                            End If
                        End If
    
                    Next
    
                    For Each strModel As String In lstModels
                        nodMake.Nodes.Add(strModel)
                    Next
                Next
            Next
    
            ' Showing the categories nodes
            For Each nodYear As TreeNode In nodRoot.Nodes
                For Each nodMake As TreeNode In nodYear.Nodes
                    For Each nodModel As TreeNode In nodMake.Nodes
    
                        Dim lstCategories As ArrayList = New ArrayList()
    
                        For Each part As PartDescription In parts
                            If (nodYear.Text = part.CarYear.ToString()) And 
                                    (nodMake.Text = part.Make) And 
                                    (nodModel.Text = part.Model) Then
                                If Not lstCategories.Contains(part.Category) Then
                                    lstCategories.Add(part.Category)
                                End If
                            End If
                        Next
    
                        For Each strCategory As String In lstCategories
                            nodModel.Nodes.Add(strCategory)
                        Next
                    Next
                Next
            Next
    End Sub
  2. Save the file

The Number of Child Nodes

The number of nodes in the TreeNode objects is stored in the TreeNodeCollection.Count property. To get the current number of nodes in the tree view, you can call the TreeView.GetNodeCount() method. Its syntax is:

Public Function GetNodeCount(includeSubTrees As Boolean) As Integer

Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            . . . No Change

            Controls.Add(tvwCountries)

            Dim NodeCount As Integer = tvwCountries.GetNodeCount(True)
            Text = CStr(NodeCount)
End Sub

This would produce:

Countries Statistics

If you create a node and add it to a branch that already contains another node, the new node is referred to as a sibling to the existing child node.

The Nodes of a Node

In our introduction, we saw that a node, any node, could have as many nodes as you judge necessary. To support this, the TreeNode class is equipped with a property called Nodes, which, like that of the TreeView class, is based on the TreeNodeCollection class. This allows you to refer to the list of children of the node that this Nodes property belongs to. With this information, you can further create or manipulate child nodes of any node as you wish.

Node Selection

Besides looking at a node, probably the primary action a user performs on a tree is to select an item. To select a node in the tree, the user can click it. To programmatically select a node, assign its reference to the TreeView.SelectedNode property. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodAfrica As TreeNode = New TreeNode("Africa")
            Dim nodAmerica As TreeNode = New TreeNode("America")
            Dim nodEurope As TreeNode = New TreeNode("Europe")
            Dim nodContinents() As TreeNode = {nodAfrica, nodAmerica, nodEurope}

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            tvwCountries.SelectedNode = nodAmerica

            Controls.Add(tvwCountries)
End Sub

After selecting a node, the tree view indicates the item selected by highlighting it. In the following picture, the America node is selected:

Countries Statistics

To programmatically find out what item is selected in the tree, get the value of the TreeView.SelectedNode Boolean property. If no node is selected, this property produces null. Alternatively, you can check the value of a node's TreeNode.IsSelected Boolean property to find out if it is currently selected.

Node Edition

After locating a node, the user may want to change its text. To change the string of a node, it must be put to edit mode. To do this, you can call the TreeNode.BeginEdit() method. Its syntax is:

Public Sub BeginEdit

When a node is in edit mode, the caret blinks in its edit box section. The user can then type a new string or edit the existing string. After setting the (new) string, the user can press Enter or may click somewhere. At this time, you need to indicate that the user has finished this operation. To do this, you can call the TreeNode.EndEdit() method. Its syntax is:

Public Sub EndEdit(cancel As Boolean)

Just before this method, you can check the content of the string that was added or edited. This allows you to accept or reject the change. The argument to the EndEdit() method allows you to validate or cancel the editing action.

Node Location

As mentioned already, the nodes of a tree view are stored in a collection of type TreeNodeCollection. Every time you create a new node, it occupies a position inside the tree. Each node is represented by the Item indexed property of this collection. The first node of the tree has an index of 0.

When you call the TreeNodeCollection.Add() method to create a node, the new branch is added at the end of the list of its siblings. If you want, you can add a new child somewhere in the tree. To do this, you would call the TreeNodeCollection.Insert() method. Its syntax is:

Public Overridable Sub Insert(index As Integer, node As TreeNode)

The first argument to this method is the index that the new node will occupy when created. The second argument is a reference to the new node to be created. Here is an example of using it:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodContinents() As TreeNode = 
                   { 
                       New TreeNode("Africa"), 
                       New TreeNode("America"), 
                       New TreeNode("Asia"), 
                       New TreeNode("Europe") 
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            tvwCountries.Nodes.Insert(1, New TreeNode("Neptune"))
            Controls.Add(tvwCountries)
End Sub

This would produce:

Countries Statistics

Another technique you can use to locate a node consists of using some coordinates. To do this, you can call the TreeView.GetNodeAt() method that is overloaded with two versions whose syntaxes are:

Public Function GetNodeAt(x As Integer, y As Integer) As TreeNode
Public Function GetNodeAt(pt As Point) As TreeNode

To use this method, you must know either the Point location or the x and y coordinates of the node. If you provide valid arguments to this method, it returns a reference to the TreeNode located at the argument. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodContinents() As TreeNode = 
                   { 
                       New TreeNode("Africa"), 
                       New TreeNode("America"), 
                       New TreeNode("Asia"), 
                       New TreeNode("Europe") 
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            tvwCountries.ExpandAll()
            Dim nodBranch As TreeNode = tvwCountries.GetNodeAt(22, 48)

            Controls.Add(tvwCountries)
            Text = nodBranch.Text
End Sub

This would produce:

Countries Statistics

After creating a tree, to get a reference to the first child node, you can retrieve the TreeNode.FirstNode property. You would use code as follows:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodContinents() As TreeNode = 
                   { 
                       New TreeNode("Africa"), 
                       New TreeNode("America"), 
                       New TreeNode("Asia"), 
                       New TreeNode("Europe") 
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            dim nodFirst  as  TreeNode = tvwCountries.Nodes(0).FirstNode

            Controls.Add(tvwCountries)
            Text = nodFirst.Text
End Sub

To get a reference to the last child node, retrieve the TreeNode.LastNode property. You would use code as follows:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodContinents() As TreeNode = 
                   { 
                       New TreeNode("Africa"), 
                       New TreeNode("America"), 
                       New TreeNode("Asia"), 
                       New TreeNode("Europe") 
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            Dim nodLast As TreeNode = tvwCountries.Nodes(0).FirstNode

            Controls.Add(tvwCountries)
            Text = nodLast.Text
End Sub

To get a reference to the sibling above a node, if any, you can retrieve its TreeNode.PrevNode property. To get a reference to the sibling below a node, if any, you can retrieve its TreeNode.NextNode property.

To find whether a tree view contains a certain node, you can call the TreeNodeCollection.Contains() method. Its syntax is:

Public Function Contains(node As TreeNode) As Boolean

This method expects as argument a reference to the node to look for. If the tree contains that node, the method returns true. If the node is not found, this method returns false.

Practical LearningPractical Learning: Using the Selected Node

  1. In the Class Name combo box, select tvwAutoParts
  2. In the Method Name combo box, select NodeMouseClick
  3. Implement the event as follows:
    Private Sub tvwAutoPartsNodeMouseClick(ByVal sender As Object, 
    	ByVal e As System.Windows.Forms.TreeNodeMouseClickEventArgs) 
                                           Handles tvwAutoParts.NodeMouseClick
            Dim nodClicked As TreeNode = e.Node
    
            If nodClicked.Level = 4 Then lvwAutoParts.Items.Clear()
    
            Try
                Try
                    For Each part As PartDescription In parts
    
                        If (part.Category = nodClicked.Text) And 
                            (part.Model = nodClicked.Parent.Text) And 
                            (part.Make = nodClicked.Parent.Parent.Text) And 
                            (part.CarYear.ToString() = 
    				    nodClicked.Parent.Parent.Parent.Text) Then
    
                            Dim lviAutoPart As ListViewItem = 
    			    New ListViewItem(part.PartNumber.ToString())
    
                            lviAutoPart.SubItems.Add(part.PartName)
                            lviAutoPart.SubItems.Add(part.UnitPrice.ToString())
                            lvwAutoParts.Items.Add(lviAutoPart)
                        End If
                    Next
                Catch ex As NullReferenceException
    
                End Try
            Catch ex As NullReferenceException
    
            End Try
    End Sub
  4. Under the above End Sub line, create the following procedure:
    Private Sub CalculateOrder()
            ' Calculate the current total order and update the order
            Dim SubTotal1 As Double
            Dim SubTotal2 As Double
            Dim SubTotal3 As Double
            Dim SubTotal4 As Double
            Dim SubTotal5 As Double
            Dim SubTotal6 As Double
            Dim OrderTotal As Double
    
            ' Retrieve the value of each sub total
            Try
                SubTotal1 = CDbl(txtSubTotal1.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            Try
                SubTotal2 = CDbl(txtSubTotal2.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            Try
                SubTotal3 = CDbl(txtSubTotal3.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            Try
                SubTotal4 = CDbl(txtSubTotal4.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            Try
                SubTotal5 = CDbl(txtSubTotal5.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            Try
                SubTotal6 = CDbl(txtSubTotal6.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            ' Calculate the total value of the sub totals
            OrderTotal = SubTotal1 + SubTotal2 + SubTotal3 + 
                         SubTotal4 + SubTotal5 + SubTotal6
    
            ' Display the total order in the appropriate text box
            txtTotalOrder.Text = CStr(OrderTotal)
    End Sub
  5. In the Class Name combo box, select lvwAutoParts
  6. In the Method Name combo box, select DoubleClick and implement the event as follows:
    Private Sub lvwAutoPartsDoubleClick(ByVal sender As Object, 
                                             ByVal e As System.EventArgs) 
                                             Handles lvwAutoParts.DoubleClick
            Dim lviAutoPart As ListViewItem = lvwAutoParts.SelectedItems(0)
    
            If lvwAutoParts.SelectedItems.Count = 0 Or 
                        lvwAutoParts.SelectedItems.Count > 1 Then
            End If
    
            If txtPartNumber1.Text = "" Then
                txtPartNumber1.Text = lviAutoPart.Text
                txtPartName1.Text = lviAutoPart.SubItems(1).Text
                txtUnitPrice1.Text = lviAutoPart.SubItems(2).Text
    
                txtQuantity1.Text = "1"
                txtSubTotal1.Text = lviAutoPart.SubItems(2).Text
    
                txtQuantity1.Focus()
                ' If the previous Part # text box is not empty, 
    	    ' then use the next one
            ElseIf txtPartNumber2.Text = "" Then
                txtPartNumber2.Text = lviAutoPart.Text
                txtPartName2.Text = lviAutoPart.SubItems(1).Text
                txtUnitPrice2.Text = lviAutoPart.SubItems(2).Text
    
                txtQuantity2.Text = "1"
                txtSubTotal2.Text = txtUnitPrice2.Text
                txtQuantity2.Focus()
            ElseIf txtPartNumber3.Text = "" Then
                txtPartNumber3.Text = lviAutoPart.Text
                txtPartName3.Text = lviAutoPart.SubItems(1).Text
                txtUnitPrice3.Text = lviAutoPart.SubItems(2).Text
    
                txtQuantity3.Text = "1"
                txtSubTotal3.Text = txtUnitPrice3.Text
                txtQuantity3.Focus()
            ElseIf txtPartNumber4.Text = "" Then
                txtPartNumber4.Text = lviAutoPart.Text
                txtPartName4.Text = lviAutoPart.SubItems(1).Text
                txtUnitPrice4.Text = lviAutoPart.SubItems(2).Text
    
                txtQuantity4.Text = "1"
                txtSubTotal4.Text = txtUnitPrice4.Text
                txtQuantity4.Focus()
            ElseIf txtPartNumber5.Text = "" Then
                txtPartNumber5.Text = lviAutoPart.Text
                txtPartName5.Text = lviAutoPart.SubItems(1).Text
                txtUnitPrice5.Text = lviAutoPart.SubItems(2).Text
    
                txtQuantity5.Text = "1"
                txtSubTotal5.Text = txtUnitPrice5.Text
                txtQuantity5.Focus()
            ElseIf txtPartNumber6.Text = "" Then
                txtPartNumber6.Text = lviAutoPart.Text
                txtPartName6.Text = lviAutoPart.SubItems(1).Text
                txtUnitPrice6.Text = lviAutoPart.SubItems(2).Text
    
                txtQuantity6.Text = "1"
                txtSubTotal6.Text = txtUnitPrice6.Text
                txtQuantity6.Focus()
                ' If all Part # text boxes are filled, don't do anything
            Else
                Exit Sub
            End If
    
            CalculateOrder()
    End Sub
  7. In the Class Name combo box, select txtQuantity1
  8. In the Method Name combo box, select Leave and implement the event as follows:
    Private Sub txtQuantity1Leave(ByVal sender As Object, 
                                       ByVal e As System.EventArgs) 
                                       Handles txtQuantity1.Leave
            Dim Quantity As Integer
            Dim UnitPrice As Double, SubTotal As Double
    
            ' Get the quantity of the current item
            Try
    
                Quantity = CInt(txtQuantity1.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            ' Get the unit price of the current item
            Try
                UnitPrice = CDbl(txtUnitPrice1.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            ' Calculate the current sub total
            SubTotal = Quantity * UnitPrice
    
            ' Display the new sub total in the corresponding text box
            txtSubTotal1.Text = SubTotal.ToString()
            ' Update the order
            CalculateOrder()
    End Sub
  9. In the Class Name combo box, select txtQuantity2
  10. In the Method Name combo box, select Leave and implement the event as follows:
    Private Sub txtQuantity2Leave(ByVal sender As Object, 
                                       ByVal e As System.EventArgs) 
                                       Handles txtQuantity2.Leave
            Dim Quantity As Integer
            Dim UnitPrice As Double, SubTotal As Double
    
            Try
                Quantity = CInt(txtQuantity2.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            Try
                UnitPrice = CDbl(txtUnitPrice2.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            SubTotal = Quantity * UnitPrice
            txtSubTotal2.Text = SubTotal.ToString()
    
            CalculateOrder()
    End Sub
  11. In the Class Name combo box, select txtQuantity3
  12. In the Method Name combo box, select Leave and implement the event as follows:
    Private Sub txtQuantity3Leave(ByVal sender As Object, 
                                       ByVal e As System.EventArgs) 
                                       Handles txtQuantity3.Leave
            Dim Quantity As Integer
            Dim UnitPrice As Double, SubTotal As Double
    
            Try
                Quantity = CInt(txtQuantity3.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            Try
                UnitPrice = CDbl(txtUnitPrice3.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            SubTotal = Quantity * UnitPrice
            txtSubTotal3.Text = SubTotal.ToString()
    
            CalculateOrder()
    End Sub
  13. In the Class Name combo box, select txtQuantity4
  14. In the Method Name combo box, select Leave and implement the event as follows:
    Private Sub txtQuantity4Leave(ByVal sender As Object, 
                                       ByVal e As System.EventArgs) 
                                       Handles txtQuantity4.Leave
            Dim Quantity As Integer
            Dim UnitPrice As Double, SubTotal As Double
    
            Try
                Quantity = CInt(txtQuantity4.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            Try
                UnitPrice = CDbl(txtUnitPrice4.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            SubTotal = Quantity * UnitPrice
            txtSubTotal4.Text = SubTotal.ToString()
    
            CalculateOrder()
    End Sub
  15. In the Class Name combo box, select txtQuantity5
  16. In the Method Name combo box, select Leave and implement the event as follows:
    Private Sub txtQuantity5Leave(ByVal sender As Object, 
                                       ByVal e As System.EventArgs) 
                                       Handles txtQuantity5.Leave
            Dim Quantity As Integer
            Dim UnitPrice As Double, SubTotal As Double
    
            Try
                Quantity = CInt(txtQuantity5.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            Try
                UnitPrice = CDbl(txtUnitPrice5.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            SubTotal = Quantity * UnitPrice
            txtSubTotal5.Text = SubTotal.ToString()
    
            CalculateOrder()
    End Sub
  17. In the Class Name combo box, select txtQuantity6
  18. In the Method Name combo box, select Leave and implement the event as follows:
    Private Sub txtQuantity6Leave(ByVal sender As Object, 
                                       ByVal e As System.EventArgs) 
                                       Handles txtQuantity6.Leave
            Dim Quantity As Integer
            Dim UnitPrice As Double, SubTotal As Double
    
            Try
                Quantity = CInt(txtQuantity6.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            Try
                UnitPrice = CDbl(txtUnitPrice6.Text)
            Catch
                MsgBox("Invalid Value")
            End Try
    
            SubTotal = Quantity * UnitPrice
            txtSubTotal6.Text = SubTotal.ToString()
    
            CalculateOrder()
    End Sub
  19. In the Class Name combo box, select btnRemove1
  20. In the Method Name combo box, select Click and implement the event as follows:
    Private Sub btnRemove1Click(ByVal sender As Object, 
                                     ByVal e As System.EventArgs) 
                                     Handles btnRemove1.Click
            txtPartNumber1.Text = ""
            txtPartName1.Text = ""
            txtUnitPrice1.Text = "0.00"
            txtQuantity1.Text = "0"
            txtSubTotal1.Text = "0.00"
    
            CalculateOrder()
    End Sub
  21. In the Class Name combo box, select btnRemove2
  22. In the Method Name combo box, select Click and implement the event as follows:
    Private Sub btnRemove2Click(ByVal sender As Object, 
                                     ByVal e As System.EventArgs) 
                                     Handles btnRemove2.Click
            txtPartNumber2.Text = ""
            txtPartName2.Text = ""
            txtUnitPrice2.Text = "0.00"
            txtQuantity2.Text = "0"
            txtSubTotal2.Text = "0.00"
    
            CalculateOrder()
    End Sub
  23. In the Class Name combo box, select btnRemove3
  24. In the Method Name combo box, select Click and implement the event as follows:
    Private Sub btnRemove3Click(ByVal sender As Object, 
                                     ByVal e As System.EventArgs) 
                                     Handles btnRemove3.Click
            txtPartNumber3.Text = ""
            txtPartName3.Text = ""
            txtUnitPrice3.Text = "0.00"
            txtQuantity3.Text = "0"
            txtSubTotal3.Text = "0.00"
    
            CalculateOrder()
    End Sub
  25. In the Class Name combo box, select btnRemove4
  26. In the Method Name combo box, select Click and implement the event as follows:
    Private Sub btnRemove4Click(ByVal sender As Object, 
                                     ByVal e As System.EventArgs) 
                                     Handles btnRemove4.Click
            txtPartNumber4.Text = ""
            txtPartName4.Text = ""
            txtUnitPrice4.Text = "0.00"
            txtQuantity4.Text = "0"
            txtSubTotal4.Text = "0.00"
    
            CalculateOrder()
    End Sub
  27. In the Class Name combo box, select btnRemove5
  28. Double-click the fifth Remove button and implement its event as follows:
    Private Sub btnRemove5Click(ByVal sender As Object, 
                                     ByVal e As System.EventArgs) 
                                     Handles btnRemove5.Click
            txtPartNumber5.Text = ""
            txtPartName5.Text = ""
            txtUnitPrice5.Text = "0.00"
            txtQuantity5.Text = "0"
            txtSubTotal5.Text = "0.00"
    
            CalculateOrder()
    End Sub
  29. In the Class Name combo box, select btnRemove6
  30. In the Method Name combo box, select Click and implement the event as follows:
    Private Sub btnRemove6Click(ByVal sender As Object, 
                                     ByVal e As System.EventArgs) 
                                     Handles btnRemove6.Click
            txtPartNumber6.Text = ""
            txtPartName6.Text = ""
            txtUnitPrice6.Text = "0.00"
            txtQuantity6.Text = "0"
            txtSubTotal6.Text = "0.00"
    
            CalculateOrder()
    End Sub
  31. In the Class Name combo box, select btnClose
  32. In the Method Name combo box, select Click and implement the event as follows:
    Private Sub btnCloseClick(ByVal sender As Object, 
                                   ByVal e As System.EventArgs) 
                                   Handles btnClose.Click
            End
    End Sub
  33. Execute the application to test it
     
  34. After using it, close the form

Deleting Nodes

When a tree contains a few nodes, the user may want to delete some of them, for any reason. To delete a node, you can call the TreeNodeCollection.Remove() method. Its syntax is:

Public Sub Remove(node As TreeNode)

This method expects a reference to the node you want to delete. Another solution you can use would consist of locating the node by its index. To do this, you would call the TreeNodeCollection.RemoveAt() method. Its syntax is:

Public Overridable Sub RemoveAt(index As Integer)

When calling this method, pass the index of the node to be deleted. If you are already at that node and you want to remove it, you can call the TreeNode.Remove() method. Its syntax is:

Public Sub Remove

One of the characteristics of a tree in the real world is that, if you cut a branch, the branches attached to it and their leaves are cut too. In the same way, if you call any of these Remove() or RemoveAt() methods to delete a node, its children, if any, would be deleted too.

To remove all nodes of a tree view, you can call the TreeNodeCollection.Clear() method. Its syntax is:

Public Overridable Sub Clear

This method is used to get rid of all nodes of a tree.

Characteristics of a Tree View

 

The Path to a Node

After a node has been added to a tree, it holds a position relative to its parent and its existence depends on that parent. To keep track of its "ancestry", each node has a path that can be used to identify its parent and its grand-parent(s), if any. To know the path of a node from itself to the root, you can access its TreeNode.FullPath property. This property produces a string made of sections separated by a specific character identified as the TreeView.PathSeparator property. By default, this character is the backslash, following the conventions of the operating system. If you want to use a different character or string, assign it to the PathSeparator property. To know what character or string a tree view is using as the separator, you can retrieve the value of its PathSeparator property.

Hot Tracking

In order to select an item, the user must click it or navigate to it using the keyboard. Alternatively, if you want the items to be underlined when the mouse passes over them, set to true the TreeView.HotTracking Boolean property. Its default value is false. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.HotTracking = True

            Controls.Add(tvwCountries)

            Dim nodContinents() As TreeNode = 
                   { 
                       New TreeNode("Africa"), 
                       New TreeNode("America"), 
                       New TreeNode("Asia"), 
                       New TreeNode("Europe") 
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)
End Sub

This would produce:

Countries Statistics

The Intermediary Lines of Related Nodes

As mentioned already, a tree view appears as a list of items arranged like a tree. This implies a relationship of parent-child among the items in the control. To indicate this relationship between two nodes, a line is drawn from one to another. Based on this, a line from a node on top of another node under it indicates that the one on top is the parent to the one under it.

The presence or absence of the lines among related nodes is controlled by the TreeView.ShowLines Boolean property. By default, this property is set to true (in the .NET Framework, some other libraries have it set by default to false). If this property is set to false, the lines between the nodes would not display. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.ShowLines = False

            Controls.Add(tvwCountries)

            Dim nodContinents() As TreeNode = 
                   { 
                       New TreeNode("Africa"), 
                       New TreeNode("America"), 
                       New TreeNode("Asia"), 
                       New TreeNode("Europe") 
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)
End Sub

This would produce:

Countries Statistics

The Root Lines

If you create a tree that has more than one root, a line is drawn among those root nodes. Here is an example:

Countries Statistics

The presence or absence of this type of line is controlled by the TreeView.ShowRootLines Boolean property.

Node Indentation

Indentation is the ability for a child node to be aligned to the right with regards to its parent. The general distance from the left border of the parent to the left border of the child is partially controlled by the TreeView.Indent property which is an integer. If the default distance doesn't suit you, you can change it by assigning a positive number to the control's Indent property.

Full Row Selection

When the user clicks an item, that node becomes highlighted for the length of its string. If you want, you can show the highlighting on the selected node but from the left to the right borders of the tree view. To do this, you can set the TreeView.FullRowSelect Boolean property to true. Its default value is false. For the TreeView.FullRowSelect property to work, the ShowLines property must be set to false. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.HotTracking = True
            tvwCountries.ShowLines = False
            tvwCountries.FullRowSelect = True

            Controls.Add(tvwCountries)

            Dim nodContinents() As TreeNode = 
                   { 
                       New TreeNode("Africa"), 
                       New TreeNode("America"), 
                       New TreeNode("Asia"), 
                       New TreeNode("Europe") 
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)
End Sub

This would produce:

Countries Statistics

Hiding Selection After Losing Focus

We saw that, to select an item, the user can click it. If the user clicks another control, the node that was selected in the tree view loses its highlighting because the control has lost focus. When the focus moves to another control, if you want the selected node of the tree view to preserve its highlighting, set to false the TreeView.HideSelection Boolean property. Its default value is true.

The + and - Buttons

At this time, we have seen that some nodes have children and some don't. When a node has at least one child, the node indicates this by displaying a + button. If the user clicks the + button, the node expands, displays a list of its children, and the button becomes -. The presence or absence of the + and - buttons is controlled by the TreeView.ShowPlusMinus Boolean property. By default, this property is set to true. If you don't want the parent nodes to display the + or - button, set this property to false.

Expanding and Collapsing Tree Nodes

When a node displays a + button and the user clicks that button, the node displays its child(ren). This action is referred to as expanding the node. To programmatically expand a node, call its TreeNode.Expand() method. Its syntax is:

Public Sub Expand

This method only expands the node that calls it but if its children have their own children, they are not expanded.  To expand a node and its children that have nodes, you can call its TreeNode.ExpandAll() method. Its syntax is:

Public Sub ExpandAll

To find out if a node is expanded, check the value of its TreeNode.IsExpanded property.

To expand other nodes of the tree view, the user can continue clicking each node that has a + button as necessary. To programmatically expand all nodes of a tree view, call its TreeView.ExpandAll() method. Its syntax is:

Public Sub ExpandAll

If a node is displaying a - button, it indicates that it is showing the list of its children. To hide the list, the user can click the - button. This action is referred to as collapsing the node. To programmatically collapse a node, call its TreeNode.Collapse() method whose syntax is:

Public Sub ExpandAll

The user can do this for each node that is expanded. To programmatically collapse all nodes of a tree view, call its TreeView.CollapseAll() method. Its syntax is:

Public Sub CollapseAll

Tree Nodes and Check Boxes

Besides the strings (and some small pictures as we will see later), the nodes of a tree view can display a check box on their left side. The presence or absence of the check box is controlled by the CheckBoxes Boolean property whose default value is false. If you want to display the check boxes, set this property to true. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.CheckBoxes = True

            Controls.Add(tvwCountries)

            Dim nodContinents() As TreeNode = 
                   { 
                       New TreeNode("Africa"), 
                       New TreeNode("America"), 
                       New TreeNode("Asia"), 
                       New TreeNode("Europe") 
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)
End Sub

This would produce:

Countries Statistics

If you equip the nodes with check boxes, the user can click an item to select it independently of the check box. The user can also click the check box, which would place a check mark in the box. To programmatically check the box, you can assign a true value to the node's Checked property.

When a check mark has been placed in a node's check box, the tree view fires an AfterCheck event, which is handled by the TreeViewEventHandler delegate. The AfterCheck event is carried by the TreeViewEventArgs class. One of properties of this class is called Action, which specifies why or how the event occurred. The Action property is in fact a value based on the TreeViewAction enumerator. Its members are:

ByKeyboard: This indicates that the event was fired by pressing a key

ByMouse: This indicates that the event was fired based on an action on the mouse

Collapse: This indicates that event was fired when the tree collapsed

Expand: This indicates that the event was fired when the tree expanded

Unknown: None of the above reasons caused the event, but the event was fired

The other property of the TreeViewEventArgs class is called Node. This member is of type TreeNode. It carries a reference to the node that fired the event, whether it was clicked, checked, expanded, or collapsed.

To programmatically find out if a node is checked, check the value of its Checked property.

Tree Nodes and Icons

Each of the nodes we have used so far displayed a simple piece of text. To enhance the appearance of a node, besides its text, you can display a small icon to the left of its string. To do this, you must first create an ImageList control and assign it to the TreeView.ImageList property.

When creating a node, if you plan to display an icon next to it, you can use the following constructor of the TreeNode class:

Public Sub New ( 
	text As String, 
	imageIndex As Integer, 
	selectedImageIndex As Integer 
)

This constructor allows you to specify the text that the node will display, the index of the picture it will use in the ImageList property, and the picture it will display when it is selected.

If you are creating a node with its children and you want to specify its pictures, use the following constructor of the TreeNode class:

Public Sub New ( 
	text As String, 
	imageIndex As Integer, 
	selectedImageIndex As Integer, 
	children As TreeNode() 
)

Just as done previously, after defining the TreeNode object, you can add it to the tree by passing it to the TreeNodeCollection.Add() method. In the same way, you can create an array of TreeNode objects and pass it to the TreeNodeCollection.AddRange() method.

Practical LearningPractical Learning: Associating Icons With Nodes

  1. Display the Central form.
    To create an icon, on the main menu, click Project -> Add New Item...
  2. In the Templates list, click Icon File
  3. Set the Name to cpap1 and click Add
  4. Right-click the white area and click Delete Image Type
  5. Design the 16x16, 16 colors version of the icon as follows:
     
    House
  6. On the main menu, click File -> Save cpap1.ico
  7. On the main menu, click File -> Close
  8. On the main menu, click Project -> Add New Item...
  9. In the Templates list, click Icon File
  10. Set the Name to cpap2 and click Add
  11. Right-click the white area and click Delete Image Type
  12. Design the 16x16, 16 colors version of the icon as follows:
     
  13. On the main menu, click File -> Save cpap2.ico
  14. On the main menu, click File -> Close
  15. On the main menu, click Project -> Add New Item...
  16. In the Templates list, click Icon File
  17. Set the Name to year1 and click Add
  18. Right-click the white area and click Delete Image Type
  19. Design the 16x16, 16 colors version of the icon as follows:
     
  20. On the main menu, click File -> Save make2.ico
  21. On the main menu, click File -> Close
  22. On the main menu, click Project -> Add New Item...
  23. In the Templates list, click Icon File
  24. Set the Name to year2 and click Add
  25. Right-click the white area and click Delete Image Type
  26. Design the 16x16, 16 colors version of the icon as follows:
     
  27. On the main menu, click File -> Save year2.ico
  28. On the main menu, click File -> Close
  29. On the main menu, click Project -> Add New Item...
  30. In the Templates list, click Icon File
  31. Set the Name to make1 and click Add
  32. Right-click the white area and click Delete Image Type
  33. Design the 16x16, 16 colors version of the icon as follows:
     
    Icon Design: Diamond
  34. On the main menu, click File -> Save make1.ico
  35. On the main menu, click File -> Close
  36. On the main menu, click Project -> Add New Item...
  37. In the Templates list, click Icon File
  38. Set the Name to make2 and click Add
  39. Right-click the white area and click Delete Image Type
  40. Design the 16x16, 16 colors version of the icon as follows:
     
    Icon Design: Diamond
  41. On the main menu, click File -> Save make2.ico
  42. On the main menu, click File -> Close
  43. On the main menu, click Project -> Add New Item...
  44. In the Templates list, click Icon File
  45. Set the Name to model1 and click Add
  46. Right-click the white area and click Delete Image Type
  47. Design the 16x16, 16 colors version of the icon as follows:
     
  48. On the main menu, click File -> Save model1.ico
  49. On the main menu, click File -> Close
  50. On the main menu, click Project -> Add New Item...
  51. In the Templates list, click Icon File
  52. Set the Name to model2 and click Add
  53. Right-click the white area and click Delete Image Type
  54. Design the 16x16, 16 colors version of the icon as follows:
     
  55. On the main menu, click File -> Save model2.ico
  56. On the main menu, click File -> Close
  57. On the main menu, click Project -> Add New Item...
  58. In the Templates list, click Icon File
  59. Set the Name to category1 and click Add
  60. Right-click the white area and click Delete Image Type
  61. Design the 16x16, 16 colors version of the icon as follows:
     
  62. On the main menu, click File -> Save category1.ico
  63. On the main menu, click File -> Close
  64. On the main menu, click Project -> Add New Item...
  65. In the Templates list, click Icon File
  66. Set the Name to category2 and click Add
  67. Right-click the white area and click Delete Image Type
  68. Design the 16x16, 16 colors version of the icon as follows:
     
    Icon Design: Minus
  69. On the main menu, click File -> Save category2.ico
  70. On the main menu, click File -> Close
  71. Display the form.
    In the Toolbox, click ImageList and click the form
  72. In the Properties window, click (Name) and type imgAutoParts
  73. Click the ellipsis button of the Images field
  74. In Image Collection Editor, click Add
  75. Locate the folder that contains the icons you created and display it in the Look In combo box
  76. Select cpap1.ico and click Open
  77. In the same way, add the other pictures in the following order: cpap2.ico, year1.ico, year2.ico, make1.ico, make2.ico, model1.ico, model2.ico, category1.ico, and category1.ico
     
    Image Collection Editor
  78. Click OK
  79. On the form, click the tree view
  80. In the Properties window, click ImageList, then click the arrow of its combo box and select imgAutoParts
  81. Access the Central.vb source file and change the code of the Load event as follows:
    Private Sub CentralLoad(ByVal sender As Object, 
                                 ByVal e As System.EventArgs) 
                                 Handles Me.Load
        Dim nodRoot As TreeNode = 
    	tvwAutoParts.Nodes.Add("College Park Auto-Parts", 
                                              "College Park Auto-Parts", 0, 1)
    
            ' This is simply used to initialize the whole array with empty parts
            ' This is just to make sure that each member of the array is defined
            For i As Integer = Date.Today.Year To 1960 Step -1
                nodRoot.Nodes.Add(CStr(i), CStr(i), 2, 3)
            Next
    
            ' Expand the root node
            tvwAutoParts.ExpandAll()
    
            . . . No Change
    
            ' Showing the makes nodes
            For Each nodYear As TreeNode In nodRoot.Nodes
    
                Dim lstMakes As ArrayList = New ArrayList()
    
                For Each part As PartDescription In parts
    
                    If nodYear.Text = part.CarYear.ToString() Then
                        If Not lstMakes.Contains(part.Make) Then
                            lstMakes.Add(part.Make)
                        End If
                    End If
    
                Next
    
                For Each strMake As String In lstMakes
                    nodYear.Nodes.Add(strMake, strMake, 4, 5)
                Next
            Next
    
            ' Showing the models nodes
            For Each nodYear As TreeNode In nodRoot.Nodes
                For Each nodMake As TreeNode In nodYear.Nodes
    
                    Dim lstModels As ArrayList = New ArrayList()
    
                    For Each part As PartDescription In parts
    
                        If nodYear.Text = part.CarYear.ToString() And 
                            (nodMake.Text = part.Make) Then
    
                            If Not lstModels.Contains(part.Model) Then
                                lstModels.Add(part.Model)
                            End If
                        End If
    
                    Next
    
                    For Each strModel As String In lstModels
                        nodMake.Nodes.Add(strModel, strModel, 6, 7)
                    Next
                Next
            Next
    
            ' Showing the categories nodes
            For Each nodYear As TreeNode In nodRoot.Nodes
                For Each nodMake As TreeNode In nodYear.Nodes
                    For Each nodModel As TreeNode In nodMake.Nodes
    
                        Dim lstCategories As ArrayList = New ArrayList()
    
                        For Each part As PartDescription In parts
                            If (nodYear.Text = part.CarYear.ToString()) And 
                                    (nodMake.Text = part.Make) And 
                                    (nodModel.Text = part.Model) Then
                                If Not lstCategories.Contains(part.Category) Then
                                    lstCategories.Add(part.Category)
                                End If
                            End If
                        Next
    
                        For Each strCategory As String In lstCategories
                            nodModel.Nodes.Add(strCategory, strCategory, 8, 9)
                        Next
                    Next
                Next
            Next
        End Sub
  82. Execute the application to test it
     
    College Park Auto-Parts
  83. Close the form and return to your programming environment
 

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