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XML-Based Applications:
College Park Auto-Parts
 

Introduction

After our various introductions to XML, we will put it to good use with a usable application. As a meta language, XML can be used to create text-based files that can be accessed by any application that reads XML. To highly support this language, the .NET Framework provides various classes that allow you to create very effective applications without investing a lot in client/server stuff.

In this lesson, we are going to create an application for a business that sells auto parts. The items sold in the store and the inventory are stored as XML files. When an employee is performing a customer order, we make the application friendly with lists that allow the user to select the necessary information using combo boxes. These include the year, the make and the model that allow to identify the specific car that a part is made for. After selecting the necessary parts, the employee can save the order. The order also is saved as an XML file.

All the orders of one particular day are saved to a common file. This allows the management to review the orders for a particular day. To review such orders, they can open another form that is equipped with a Date Picker and a DataGrid controls. The employee selects a date and the grid displays the list of items sold for that day, if any.

Prerequisites: To follow this lesson, you should be familiar with:

 

Practical Learning Practical Learning: Introducing the Application
  1. Start Microsoft Visual Studio .NET and create a Windows Application named CPAP3
  2. To add a new XML file, on the main menu, click File -> New -> File ...
  3. In the Templates list of the Add New Item dialog box, click XML File and click Open
  4. Complete the file as follows:
      
    <?xml version="1.0" encoding="utf-8" ?>
<Cars>
	<Make MakeName="Acura">
		<Model>Integra GS 1.8L L4</Model>
		<Model>MDX 3.5L V6</Model>
		<Model>NSX 3.0L V6</Model>
		<Model>NSX 3.2L V6</Model>
		<Model>TL 3.2L V6</Model>
	</Make>
	<Make MakeName="Audi">
		<Model>A4 Quattro 1.8L Turbo</Model>
		<Model>A4 Quattro 3.0L V6</Model>
		<Model>S4 2.7L V6</Model>
	</Make>
	<Make MakeName="BMW">
		<Model>325I 2.5L L6</Model>
		<Model>325XI 2.5L L6</Model>
		<Model>745I 4.4L V8</Model>
		<Model>Z3 Coupe 3.0L L6</Model>
	</Make>
</Cars>
  5. To save it, on the main menu, click File -> Save XMLFile1
  6. Locate the folder that contains the current project and display it in the Save In combo box
  7. Double-click its bin folder to  display it in the Save In combo box
  8. Set the Name to Cars and click Save
  9. To add a new XML file, on the main menu, click File -> New -> File... In the Templates list of the Add New Item dialog box, click XML File and click Open
  10. Fill it up with a few parts as follows:
      
    <?xml version="1.0" encoding="utf-8" ?>
<PartCategories>
	<PartCategory>Accessories-Exterior</PartCategory>
	<PartCategory>Belt Drive System</PartCategory>
	<PartCategory>Body-Exterior</PartCategory>
	<PartCategory>Body-Interior</PartCategory>
	<PartCategory>Brake System</PartCategory>
	<PartCategory>Clutch</PartCategory>
	<PartCategory>Cooling System</PartCategory>
	<PartCategory>Drivetrain</PartCategory>
	<PartCategory>Electrical</PartCategory>
  	<PartCategory>Miscellaneous</PartCategory>
</PartCategories>
  11. To save it, on the Standard toolbar, click the Save button
  12. Make sure the bin folder is displaying in the Save In combo box.
    Set the file name to PartCategories
  13. Add another XML file and fill it up with a few parts as follows:
      
    <?xml version="1.0" encoding="utf-8" ?>
<Parts>
	<Part>
		<PartNumber>293749</PartNumber>
		<CarYear>2005</CarYear>
		<Make>Acura</Make>
		<Model>NSX 3.0L V6</Model>
		<PartName Category="Engine">Oil Filter</PartName>
		<UnitPrice>8.85</UnitPrice>
	</Part>
	<Part>
		<PartNumber>283759</PartNumber>
		<CarYear>2002</CarYear>
		<Make>Audi</Make>
		<Model>A4 Quattro 1.8L Turbo</Model>
		<PartName Category="Clutch">Clutch Release Bearing</PartName>
		<UnitPrice>55.50</UnitPrice>
	</Part>
	<Part>
		<PartNumber>368374</PartNumber>
		<CarYear>2002</CarYear>
		<Make>Audi</Make>
		<Model>A4 Quattro 1.8L Turbo</Model>
		<PartName Category="Electrical">Alternator</PartName>
		<UnitPrice>305.50</UnitPrice>
	</Part>
	<Part>
		<PartNumber>485704</PartNumber>
		<CarYear>2002</CarYear>
		<Make>Audi</Make>
		<Model>A4 Quattro 1.8L Turbo</Model>
		<PartName Category="Engine">Oil Filter</PartName>
		<UnitPrice>5.50</UnitPrice>
	</Part>
	<Part>
		<PartNumber>491759</PartNumber>
		<CarYear>1998</CarYear>
		<Make>BMW</Make>
		<Model>325I 2.5L L6</Model>
		<PartName Category="Ignition">Ignition Coil</PartName>
		<UnitPrice>60.85</UnitPrice>
	</Part>
</Parts>
  14. Save it as Parts.xml in the bin folder

Application Design

To make our application intuitive, we will create a few objects as follows:

  1. New Make: This dialog box allows the user to create a new car make that will eventually be used to identify a part
  2. New Model: This dialog box is used to create a new car model
  3. New Part Category: In order to restrict the search of a part, the items of this store will be categorized. This dialog box is used to create the categories of items
  4. New Part: This is the main form used to create each part or item sold in the store. To create an item, the user must specify the year of the car, its model, and the type or category of the item. Then the user must create a name for the part; this can also be a short description. The user must also specify the price of the item. For inventory purposes, each item sold in the store must have a number. To make this easy, we will write our own code to automatically generate a number but the user can still change it.
    Once the item is ready, the user can click the Add Part button. This creates the item and stores it in the XML file used for general inventory
  5. Order Processing: This is the form used to select a part or an item requested by a customer

When designing this type of application, you should keep in mind to make it as user friendly as possible, which is what we did. Still, you are free to change our design to what suits you.

Practical Learning Practical Learning: Designing the Application
  1. To add a new form, on the main menu, click Project -> Add Windows Form...
  2. In the Templates list of the Add New Item dialog box, make sure Windows Forms is selected.
    Set the Name to NewMake and press Enter
  3. Design the form as follows:
     
    College Park Auto-Parts: New Make Form - Form Design
    Control Name Text Other Properties
    Label   New Car Make:  
    TextBox txtNewMake   Modifiers: Public
    Button btnOK OK DialogResult: OK
    Button btnCancel Cancel DialogResult: Cancel
    Form     AcceptButton: btnOK
    CancelButton: btnCancel
    FormBorderStyle: FixedDialog
    MaximizeBox: False
    MinimizeBox: False
    ShowInTaskbar: False
    StartPosition: CenterScreen
  4. To add a new form, on the main menu, click Project . Add Windows Form...
  5. Set the Name to NewModel and press Enter
  6. Design the form as follows:
     
    College Park Auto-Parts: New Car Model - Form Design
    Control Name Text Other Properties
    Label   Make:  
    ComboBox cboMakes   DropDownStyle: DropDownList
    Button btnNewMake New Make  
    Label   Model:  
    TextBox txtNewModel    
    Button btnOK OK DialogResult: OK
    Button btnCancel Cancel DialogResult: Cancel
    Form     AcceptButton: btnOK
    CancelButton: btnCancel
    FormBorderStyle: FixedDialog
    MaximizeBox: False
    MinimizeBox: False
    ShowInTaskbar: False
    StartPosition: CenterScreen
  7. Double-click the New Make button
  8. In the top section of the file, type Imports System.Xml
  9. Implement the Click event as follows:
      
    Private Sub btnNewMake_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNewMake.Click
        Dim frmNewMake As NewMake = New NewMake

        frmNewMake.ShowDialog()
End Sub
  10. To add a new form, on the main menu, click Project -> Add Windows Form
  11. Set the Name to NewPartCategory and press Enter
  12. Design the form as follows:
     
    Collge Park Auto-Parts: New Part Category - Form Design
    Control Name Text Other Properties
    Label   New Category:  
    TextBox txtNewCategory   Modifiers: Public
    Button btnOK OK DialogResult: OK
    Button btnCancel Cancel DialogResult: Cancel
    Form   New Make AcceptButton: btnOK
    CancelButton: btnCancel
    FormBorderStyle: FixedDialog
    MaximizeBox: False
    MinimizeBox: False
    ShowInTaskbar: False
    StartPosition: CenterScreen
  13. To add a new form, on the main menu, click Project -> Windows Forms
  14. Set the Name to NewPart and press Enter
  15. Design the form as follows:
     
    New Part
    Control Name Text Other Properties
    Label   Year:  
    ComboBox cboYears   DropDownStyle: DropDownList
    Modifiers: Public
    Label   Make:  
    ComboBox cboMakes   DropDownStyle: DropDownList
    Modifiers: Public
    Button btnNewMake New Make  
    Label   Model:  
    ComboBox cboModels   DropDownStyle: DropDownList
    Modifiers: Public
    Button btnNewModel New Model  
    Label   Part Category:  
    ComboBox cboPartCategories   DropDownStyle: DropDownList
    Modifiers: Public
    Button btnNewCategory New Category  
    Label   Part Name:  
    TextBox txtPartName   Modifiers: Public
    Label   Unit Price:  
    TextBox txtUnitPrice 0.00 Modifiers: Public
    TextAlign: Right
    Label   Part #:  
    TextBox txtPartNumber 000000 Modifiers: Public
    TextAlign: Right
    Button btnAddPart Add Part  
    Button btnClose Close  
    Form     AcceptButton: btnAdd
    CancelButton: btnClose
    MaximizeBox: False
    StartPosition: CenterScreen
  16. Double-click an unoccupied area of the form to access its Load event and implement its as follows:
      
    Private Sub NewPart_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ' Fill the Year combo box with years from 1960 to the coming year
        Dim i As Integer
        For i = DateTime.Now.Year + 1 To 1960 Step -1
            Me.cboYears.Items.Add(i.ToString())
        Next

        ' We will generate a random number for the item
        ' To start, we will use the miliseconds as a seed
        Dim tmeNow As DateTime = DateTime.Now
        Dim ms As Integer = tmeNow.Millisecond
        Dim rndNumber As Random = New Random(ms)

        ' Generate three randomg characters
        Dim firstCharacter As Char = ChrW(rndNumber.Next(65, 90))
        Dim secondCharacter As Char = ChrW(rndNumber.Next(65, 90))
        Dim thirdCharacter As Char = ChrW(rndNumber.Next(65, 90))
        ' Generate a random number made of 4 digits
        Dim numberPart As Integer = rndNumber.Next(1000, 9999)

        ' Exclude the digits 1 and 0 because they create confusion
        If firstCharacter = "I" Or firstCharacter = "O" Then
            firstCharacter = "A"
        End If
        If secondCharacter = "I" Or secondCharacter = "O" Then
            secondCharacter = "A"
        End If
        If thirdCharacter = "I" Or thirdCharacter = "O" Then
            thirdCharacter = "A"
        End If
        ' Generate a random number from 1 to 4
        Dim rndCombination As Integer = rndNumber.Next(1, 4)
        Dim strPartNumber As String = Nothing

        ' Create a part number using some algorithm
        If rndCombination = 1 Then
            strPartNumber = CStr(firstCharacter) & CStr(secondCharacter) & _
   	CStr(numberPart) & CStr(thirdCharacter)
        ElseIf rndCombination = 2 Then
            strPartNumber = CStr(firstCharacter) & CStr(numberPart) & _
             CStr(secondCharacter) & CStr(thirdCharacter)
        ElseIf rndCombination = 3 Then
            strPartNumber = CStr(numberPart) & CStr(firstCharacter) & _
             CStr(secondCharacter) & CStr(thirdCharacter)
        Else
            strPartNumber = CStr(rndNumber.Next(100000, 999999))
        End If

        ' Display the new number in the Part # text box
        Me.txtPartNumber.Text = strPartNumber

        ' Disable the Add Part button to indicate that the part is not ready
        Me.btnAddPart.Enabled = False
End Sub
  17. In the top section of the file, type Imports System.Xml as the first line
  18. In the Class Name combo box, select btnNewMake and, in the Method Name combo box, select Click
  19. Implement the event as follows:
      
    Private Sub btnNewMake_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnNewMake.Click
        Dim frmNewMake As NewMake = New NewMake

        frmNewMake.ShowDialog()
End Sub
  20. In the Class Name combo box, select btnNewModel and, in the Method Name combo box, select Click
  21. Implement the event as follows:
      
    Private Sub btnNewModel_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnNewModel.Click
        Dim frmNewModel As NewModel = New NewModel

        frmNewModel.ShowDialog()
End Sub
  22. In the Class Name combo box, select btnNewCategory and, in the Method Name combo box, select Click
  23. Implement the event as follows:
      
    Private Sub btnNewCategory_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnNewCategory.Click
        Dim frmCat As NewPartCategory = New NewPartCategory

        frmCat.ShowDialog()
End Sub
  24. In the Class Name combo box, select btnClose and, in the Method Name combo box, select Click
  25. Implement the Click events as follows:
      
    Private Sub btnClose_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnClose.Click
        Close()
End Sub
  26. To add a new form, on the main menu, click Project -> Add Windows Form...
  27. Set the Name to OrderProcessing and press Enter
  28. Design the form as follows:
     
    College Park Auto Parts - Order Processing - Form Design
    Control Name Text Other Properties
    GroupBox   Part Selection  
    Label   Year:  
    Label      
    ComboBox cboYears   DropDownStyle: DropDownList
    Label   Make:  
    ComboBox cboModels   DropDownStyle: DropDownList
    Label   Model:  
    ComboBox cboMakes   DropDownStyle: DropDownList
    Label   Category:  
    ComboBox cboCategories   DropDownStyle: DropDownList
    Label   Available Parts  
    ListView lvwAvailableParts   FullRowSelect: True
    GridLines: True
    Columns:
    Text TextAlign Width
    Part # Center 60
    Part Name Left 220
    Unit Price Right 60
    GroupBox   Setup  
    Button btnNewPart New Part  
    Button btnClose Close  
    GroupBox   Customer Order  
    Label   Part #  
    Label   Part Name  
    Label   Unit Price  
    Label   Qty  
    Label   Sub Total  
    Label   Keep Remove  
    TextBox txtPartNumber1    
    TextBox txtPartName1    
    TextBox txtUnitPrice1 0.00 TextAlign: Right
    TextBox txtQuantity1 0 TextAlign: Right
    TextBox txtSubTotal1 0.00 TextAlign: Right
    CheckBox chkKeepRemove1    
    TextBox txtPartNumber2    
    TextBox txtPartName2    
    TextBox txtUnitPrice2 0.00 TextAlign: Right
    TextBox txtQuantity2 0 TextAlign: Right
    TextBox txtSubTotal2 0.00 TextAlign: Right
    CheckBox chkKeepRemove2    
    TextBox txtPartNumber3    
    TextBox txtPartName3    
    TextBox txtUnitPrice3 0.00 TextAlign: Right
    TextBox txtQuantity3 0 TextAlign: Right
    TextBox txtSubTotal3 0.00 TextAlign: Right
    CheckBox chkKeepRemove3    
    TextBox txtPartNumber4    
    TextBox txtPartName4    
    TextBox txtUnitPrice4 0.00 TextAlign: Right
    TextBox txtQuantity4 0 TextAlign: Right
    TextBox txtSubTotal4 0.00 TextAlign: Right
    CheckBox chkKeepRemove4    
    TextBox txtPartNumber5    
    TextBox txtPartName5    
    TextBox txtUnitPrice5 0.00 TextAlign: Right
    TextBox txtQuantity5 0 TextAlign: Right
    TextBox txtSubTotal5 0.00 TextAlign: Right
    CheckBox chkKeepRemove5    
    TextBox txtPartNumber6    
    TextBox txtPartName6    
    TextBox txtUnitPrice6 0.00 TextAlign: Right
    TextBox txtQuantity6 0 TextAlign: Right
    TextBox txtSubTotal6 0.00 TextAlign: Right
    CheckBox chkKeepRemove6    
    Label   Order saved in  
    DateTimePicker dtpFilename   Format: Custom
    CustomFormat: ddMMMyyyy
    Button btnSave Save  
    Label   Total Order:  
    TextBox txtTotalOrder 0.00 TextAlign: Right
  29. Double an unoccupied area of the form outside of any group box to generate the form's Load event
  30. Implement the Load event as follows:
      
    Private Sub OrderProcessing_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ' Fill the Year combo box with years from 1960 to the coming year
        Dim i As Integer
        For i = DateTime.Now.Year + 1 To 1960 Step -1
            Me.cboYears.Items.Add(i.ToString())
        Next
End Sub
  31. In the top section of the file, type the following two lines:
      
    Imports System.IO
Imports System.Xml
Public Class OrderProcessing
  32. In the Class Name combo box, select btnNewPart and, in the Method Name combo box, select Click
  33. Implement its Click event as follows:
      
    Private Sub btnNewPart_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnNewPart.Click
        Dim frmPart As NewPart = New NewPart

        frmPart.ShowDialog()
End Sub
  34. In the Class Name combo box, select btn Close and, in the Method Name combo box, select Click
  35. Implement the Click event as follows:
      
    Private Sub btnClose_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnClose.Click
        Close()
End Sub
  36. Display the first or main form (Form1.vb [Design]) and design it as follows 
     
    Collge Park Auto-Parts: Switchboard Form Design
    Control Name Text
    Button btnOrderProcessing Order Processing
    Button btnNewPart New Part
    Button btnClose Close
  37. Double-click the Order Processing button and implement its Click event as follows:
      
    Private Sub btnOrderProcessing_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOrderProcessing.Click
        Dim frmOrder As OrderProcessing = New OrderProcessing

        frmOrder.ShowDialog()
End Sub
  38. In the Class Name combo box, select btnNewPart and, in the Method Name combo box, select Click
  39. Implement the Click event as follows:
      
    Private Sub btnNewPart_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnNewPart.Click
        Dim frmPart As NewPart = New NewPart

        frmPart.ShowDialog()
End Sub
  40. In the Class Name combo box, select btn Close and, in the Method Name combo box, select Click
  41. Implement the Click events as follows:
      
    Private Sub btnClose_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnClose.Click
        End
End Sub
  42. Execute the application to test it
 

Using the Document Object Model (DOM)

The main purpose of this application is to take advantage of XML and the Document Object Model (DOM) as it is implemented in the .NET Framework through the XmlDocument class. As mentioned in our lessons on XML, the XmlDocument class provides the necessary methods to create an element, to locate one, and to managed. To perform some of these operations, it gets assisted by the XmlNode and its derived classes. Based on this, we will use those classes to create parts and items sold in the store.

Before creating a part, the application must have a list of cars. To start, we created a sample XML file that contained a few cars. Here, we will all the user to add new model and add them to the file. We will create new models from the New Model dialog box.

When designing the New Part form, we equipped it with a few combo boxes. When the New Part form displays, we will make sure that those combo boxes are filled with the information that is already stored in the corresponding XML files. 

Practical Learning Practical Learning: Introducing the Document Object Model (DOM)
  1. Display the New Model form and double-click an unoccupied area of the form to access its Load event
  2. Implement the Load event as follows:
      
    Private Sub NewModel_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ' We will need a reference to the XML document
        Dim docXML As XmlDocument = New XmlDocument

        ' We will start with the Make combo box
        ' Open the Cars.xml file
        docXML.Load("Cars.xml")
        ' Get a reference to the root node
        Dim nodRoot As XmlElement = docXML.DocumentElement
        ' Locate all nodes whose name is Make
        Dim nodItems As XmlNodeList = nodRoot.GetElementsByTagName("Make")
        ' Retrieve the value of each Make node and put 
        ' that value in the Make combo box
        Dim i As Integer
        For i = 0 To nodItems.Count - 1 Step 1
            Me.cboMakes.Items.Add(nodItems.ItemOf(i).Attributes.ItemOf("MakeName").InnerText)
        Next
End Sub
  3. Access the New Part form and change its Load event as follows:
      
    Private Sub NewPart_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ' Fill the Year combo box with years from 1960 to the coming year
        Dim i As Integer
        For i = DateTime.Now.Year + 1 To 1960 Step -1
            Me.cboYears.Items.Add(i.ToString())
        Next

        ' We will need a reference to the XML document
        Dim docXML As XmlDocument = New XmlDocument

        ' Open the Cars.xml file
        docXML.Load("Cars.xml")

        ' Get a reference to the root node
        Dim nodRoot As XmlElement = docXML.DocumentElement
        ' Locate all nodes whose name is Make
        Dim nodItems As XmlNodeList = nodRoot.GetElementsByTagName("Make")
        ' Retrieve the value of each Make node and put 
        ' that value in the Make combo box
        For i = 0 To nodItems.Count - 1 Step 1
            Me.cboMakes.Items.Add(nodItems.ItemOf(i).Attributes.ItemOf("MakeName").InnerText)
        Next

        ' Open the Makes.xml file
        docXML.Load("PartCategories.xml")

        ' Get a reference to the root node
        nodRoot = docXML.DocumentElement
        ' Locate all nodes whose name is Make
        nodItems = nodRoot.GetElementsByTagName("PartCategory")
        ' Retrieve the value of each Make node and put 
        ' that value in the Make combo box
        For i = 0 To nodItems.Count - 1 Step 1
            Me.cboPartCategories.Items.Add(nodItems.ItemOf(i).InnerText)
        Next

        Me.cboPartCategories.Text = "Miscellaneous"
        ' We will generate a random number for the item
        ' To start, we will use the miliseconds as a seed
        Dim tmeNow As DateTime = DateTime.Now
        Dim ms As Integer = tmeNow.Millisecond

        ' Now we can generate a random number between 100000 and 999999
        Dim rndNumber As Random = New Random(ms)

        ' Generate three randomg characters
        Dim firstCharacter As Char = ChrW(rndNumber.Next(65, 90))
        Dim secondCharacter As Char = ChrW(rndNumber.Next(65, 90))
        Dim thirdCharacter As Char = ChrW(rndNumber.Next(65, 90))
        ' Generate a random number made of 4 digits
        Dim numberPart As Integer = rndNumber.Next(1000, 9999)

        ' Exclude the digits 1 and 0 because they create confusion
        If firstCharacter = "I" Or firstCharacter = "O" Then
            firstCharacter = "A"
        End If
        If secondCharacter = "I" Or secondCharacter = "O" Then
            secondCharacter = "A"
        End If
        If thirdCharacter = "I" Or thirdCharacter = "O" Then
            thirdCharacter = "A"
        End If
        ' Generate a random number between 1 and 3
        Dim rndCombination As Integer = rndNumber.Next(1, 4)
        Dim strPartNumber As String = 0

        ' Create a part number using some algorithm
        If rndCombination = 1 Then
            strPartNumber = CStr(firstCharacter) & CStr(secondCharacter) & _
   CStr(numberPart) & CStr(thirdCharacter)
        ElseIf rndCombination = 2 Then
            strPartNumber = CStr(firstCharacter) & CStr(numberPart) & _
             CStr(secondCharacter) & CStr(thirdCharacter)
        ElseIf rndCombination = 3 Then
            strPartNumber = CStr(numberPart) & CStr(firstCharacter) & _
             CStr(secondCharacter) & CStr(thirdCharacter)
        Else
            strPartNumber = CStr(rndNumber.Next(100000, 999999))
        End If

        ' Display the new number in the Part # text box
        Me.txtPartNumber.Text = strPartNumber

        ' Disable the OK button to indicate that the part is not ready
        Me.btnAddPart.Enabled = False
End Sub
  4. Access the Cars.xml file. To add a comment, change it as follows:
      
    <?xml version="1.0" encoding="utf-8" ?> 
<Cars>
	<!-- Each car model is organized as follows:
	       1. The first part identifies the make of the car.
	           We use a MakeName attribute of the Make element
	           to identify a make
	       2. The second part identifies the name of the model.
	-->
	<Make MakeName="Acura">
		<Model>Integra GS 1.8L L4</Model>
		<Model>MDX 3.5L V6</Model>
		<Model>NSX 3.0L V6</Model>
		<Model>NSX 3.2L V6</Model>
		<Model>TL 3.2L V6</Model>
	</Make>
	<Make MakeName="Audi">
		<Model>A4 Quattro 1.8L Turbo</Model>
		<Model>A4 Quattro 3.0L V6</Model>
		<Model>S4 2.7L V6</Model>
	</Make>
	<Make MakeName="BMW">
		<Model>325I 2.5L L6</Model>
		<Model>325XI 2.5L L6</Model>
		<Model>745I 4.4L V8</Model>
		<Model>Z3 Coupe 3.0L L6</Model>
	</Make>
</Cars>
  5. Save the file
  6. Execute the application to test it and make sure that the top combo boxes of the New Part and the New Model forms are rightly filled
  7. Close the form and return to your programming environment

Inventory Creation

The inventory of our store is created by adding items to an XML file. To do this, once again, we take advantage of the XmlDocument, the XmlNode, and its derived classes. This inventory is done using the New Part form.

We need to apply some rules in order to create an item. Early rules can make the application easier to use and maintain. For example, we must create an item only if it can be clearly identified. This makes it easy to locate it when processing an order. We explain through the comments in the code.

Practical Learning Practical Learning: Creating the Inventory
  1. Display the New Model form and double-click the New Make button
  2. Change the Click event of the btnNewMake button as follows:
      
    Private Sub btnNewMake_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNewMake.Click
        ' The new car make will come from the New Make dialog box
        Dim frmMake As NewMake = New NewMake

        ' Display the New Make dialog box and find out if the user clicked OK
        If frmMake.ShowDialog() = DialogResult.OK Then

            Dim strNewMake As String = frmMake.txtNewMake.Text

            ' If the user didn"t create a new Make, don"t do anything
            If strNewMake = "" Then
                Exit Sub
            End If

            ' Before adding the new make, check that it doesn"t exist already
            If Me.cboMakes.FindStringExact(strNewMake) > 0 Then
                Exit Sub
            End If

            ' Now you can add it
            Me.cboMakes.Items.Add(strNewMake)
            ' The user likely wants this new item selected
            Me.cboMakes.Text = strNewMake

            ' Open the Cars.xml file
            Dim docXMLFile As XmlDocument = New XmlDocument
            docXMLFile.Load("Cars.xml")

            ' Get the root node so we can explore its children
            Dim nodRoot As XmlNode = docXMLFile.DocumentElement

            ' If the car is not in the list already, create its Make node
            Dim nodNewMake As XmlNode = docXMLFile.CreateNode(XmlNodeType.Element, "Make", "")
            ' Create an attribute for the node
            CType(nodNewMake, XmlElement).SetAttribute("MakeName", strNewMake)

            ' Add the new node to the XML file
            docXMLFile.DocumentElement.AppendChild(nodNewMake)

            ' Save the file
            docXMLFile.Save("Cars.xml")
        End If
End Sub
  3. Display the New Part form and double-click the New Make button
  4. Change the Click event of the btnNewMake button as follows:
      
    Private Sub btnNewMake_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnNewMake.Click
        ' The new car make will come from the New Make dialog box
        Dim frmMake As NewMake = New NewMake

        ' Display the New Make dialog box and find out if the user clicked OK
        If frmMake.ShowDialog() = DialogResult.OK Then

            Dim strNewMake As String = frmMake.txtNewMake.Text

            ' If the user didn"t create a new Make, don"t do anything
            If strNewMake = "" Then
                Exit Sub
            End If

            ' Before adding the new make, check that it doesn"t exist already
            If Me.cboMakes.FindStringExact(strNewMake) > 0 Then
                Exit Sub
            End If

            ' Now you can add it
            Me.cboMakes.Items.Add(strNewMake)
            ' The user likely wants this new item selected
            Me.cboMakes.Text = strNewMake

            ' Open the Cars.xml file
            Dim docXMLFile As XmlDocument = New XmlDocument
            docXMLFile.Load("Cars.xml")

            ' Get the root node so we can explore its children
            Dim nodRoot As XmlNode = docXMLFile.DocumentElement

            ' If the car is not in the list already, create its Make node
            Dim nodNewMake As XmlNode = docXMLFile.CreateNode(XmlNodeType.Element, "Make", "")
            ' Create an attribute for the node
            CType(nodNewMake, XmlElement).SetAttribute("MakeName", strNewMake)

            ' Add the new node to the XML file
            docXMLFile.DocumentElement.AppendChild(nodNewMake)

            ' Save the file
            docXMLFile.Save("Cars.xml")
        End If
End Sub
  5. In the Class Name combo box, select btnNewModel
  6. In the Method Name combo box, select Click and change its event as follows:
      
    Private Sub btnNewModel_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnNewModel.Click
        ' The new car model will come from the New Model dialog box
        Dim frmModel As NewModel = New NewModel

        ' Display the New Model dialog box and find out if the user clicked OK
        If frmModel.ShowDialog() = DialogResult.OK Then

            ' Retrieve the values that the user specified
            Dim strMake As String = frmModel.cboMakes.Text
            Dim strNewModel As String = frmModel.txtNewModel.Text

            ' If the new didn"t select a Make, don"t do anything
            If strMake = "" Then
                Exit Sub
            End If
            ' If the New Model string is empty, don"t do anything
            If strNewModel = "" Then
                Exit Sub
            End If

            ' Open the Cars.xml file
            Dim docXMLFile As XmlDocument = New XmlDocument
            docXMLFile.Load("Cars.xml")

            ' Get the root node so we can explore its children
            Dim nodRoot As XmlNode = docXMLFile.DocumentElement

            ' Create a list of all Make nodes
            Dim lstMakes As XmlNodeList = docXMLFile.GetElementsByTagName("Make")

            ' Visit each Make
            Dim i As Integer
            For i = 0 To lstMakes.Count - 1 Step 1

                ' Get a reference to the current node
                Dim curMake As XmlNode = lstMakes.ItemOf(i)

                ' If, or when you find the Make
                If curMake.Attributes.ItemOf("MakeName").InnerText = strMake Then

                    ' Since we found the Make, find out if the model exists
                    Dim lstCurrentModels As XmlNodeList = curMake.ChildNodes

                    ' Check each model if the list already contains the model
                    Dim j As Integer
                    For j = 0 To lstCurrentModels.Count - 1 Step 1

                        If lstCurrentModels.ItemOf(j).InnerText = strNewModel Then

                            MsgBox("That model exists already in the database")
                            Exit Sub
                        End If
                    Next

                    ' create a child node to it
                    Dim nodModel As XmlNode = docXMLFile.CreateNode(XmlNodeType.Element, "Model", "")
                    ' Create its value using the string from the New Make dialog box
                    nodModel.InnerText = strNewModel
                    ' Add the new element at the end of the file
                    curMake.AppendChild(nodModel)

                    ' Save the file
                    docXMLFile.Save("Cars.xml")
                End If
            Next
        End If
End Sub
  7. In the Class Name combo box, select cboMakes
  8. In the Method Name combo box, select SelectedIndexChanged
  9. Implement the event as follows:
      
    Private Sub cboMakes_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles cboMakes.SelectedIndexChanged
        ' Empty the Models combo box
        Me.cboModels.Items.Clear()

        ' Find out if the user had selected a Make
        Dim strSelectedMake As String = Me.cboMakes.Text
        ' Open the Cars.xml file
        Dim docXML As XmlDocument = New XmlDocument
        docXML.Load("Cars.xml")

        ' Get a reference to the root node
        Dim nodRoot As XmlElement = docXML.DocumentElement
        ' Locate all nodes whose name is Make
        Dim nodMakes As XmlNodeList = nodRoot.GetElementsByTagName("Make")
        ' Look for the Make that is the same the user selected
        Dim i As Integer
        For i = 0 To nodMakes.Count - 1 Step 1

            ' Retrieve the value of each Make node and put
            Dim strMakeName As String = nodMakes.ItemOf(i).Attributes.ItemOf("MakeName").InnerText
            ' If you find it...
            If strMakeName = strSelectedMake Then

                ' If you find it, make a list of its models...
                Dim nodAvailableModels As XmlNodeList = nodMakes.ItemOf(i).ChildNodes
                ' ... then add each of its models to the Model combo box
                Dim j As Integer
                For j = 0 To nodAvailableModels.Count - 1 Step 1
                    Me.cboModels.Items.Add(nodAvailableModels.ItemOf(j).InnerText)
                Next
            End If
        Next

End Sub
  10. In the Class Name combo box, select btnNewCategory
  11. In the Method Name combo box, select Click
  12. Change its Click event as follows:
      
    Private Sub btnNewCategory_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnNewCategory.Click
        ' Get a reference to the New Part Category form
        Dim frmCategory As NewPartCategory = New NewPartCategory

        ' Display the New Part Category dialog box and find out if the user clicked OK
        If frmCategory.ShowDialog() = DialogResult.OK Then

            Dim strCategory As String = frmCategory.txtNewCategory.Text

            ' If the user didn"t create a new category, don't do anything
            If strCategory = "" Then
                Exit Sub
            End If

            ' Before adding the new category, check that it doesn't exist already
            If Me.cboPartCategories.FindStringExact(strCategory) > 0 Then
                Exit Sub
            End If

            ' Now you can add it
            Me.cboPartCategories.Items.Add(strCategory)
            ' The user likely wants this new item selected
            Me.cboPartCategories.Text = strCategory

            ' Open the PartCategories.xml file
            Dim docXMLFile As XmlDocument = New XmlDocument
            docXMLFile.Load("PartCategories.xml")

            ' Get the root node so we can explore its children
            Dim nodRoot As XmlNode = docXMLFile.DocumentElement

            ' If the new part is not in the list already, create its node
            Dim nodNewCategory As XmlNode = docXMLFile.CreateNode(XmlNodeType.Element, "PartCategory", "")
            ' Create text for the node
            nodNewCategory.InnerText = strCategory

            ' Add the new node to the XML file
            docXMLFile.DocumentElement.AppendChild(nodNewCategory)

            ' Save the file
            docXMLFile.Save("PartCategories.xml")
        End If
End Sub
  13. In the Class Name combo box, select txtPartName
  14. In the Method Name combo box, select TextChanged and implement its event as follows:
      
    Private Sub txtPartName_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtPartName.TextChanged
        ' If there is no part name, no need to add the item to the XML file
        If Me.txtPartName.Text = "" Then
            Me.btnAddPart.Enabled = False
        Else
            Me.btnAddPart.Enabled = True
        End If
End Sub
  15. In the Class Name combo box, select txtUnitPrice
  16. In the Method Name combo box, select TextChanged and implement its event as follows:
      
    Private Sub txtUnitPrice_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtUnitPrice.TextChanged
        ' If the price is not specified, don"t add the item to the XML file
        If Me.txtUnitPrice.Text = "" Then
            Me.btnAddPart.Enabled = False
        Else
            Me.btnAddPart.Enabled = True
        End If
End Sub
  17. In the Class Name combo box, select txtPartNumber
  18. In the Method Name combo box, select TextChanged and implement its event as follows:
      
    Private Sub txtPartNumber_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtPartNumber.TextChanged
        ' Make sure that there is a Part Number for this item
        ' Otherwise, don't add the part to the XML file
        If Me.txtPartNumber.Text = "" Then
            Me.btnAddPart.Enabled = False
        Else
            Me.btnAddPart.Enabled = True
        End If
End Sub
  19. In the Class Name combo box, select btnAddPart
  20. In the Method Name combo box, select Click and implement its event as follows:
      
    Private Sub btnAddPart_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnAddPart.Click
        ' Open the Parts.xml file
        Dim docXML As XmlDocument = New XmlDocument
        docXML.Load("Parts.xml")

        ' Before adding the new part, make sure all components are ready
        ' Otherwise, don"t add it
        If Me.cboYears.SelectedIndex < 0 Then
            MsgBox("You must specify the year. " & _
             "This will help to locate the part")
            Me.cboYears.Focus()
            Exit Sub
        End If
        If Me.cboMakes.SelectedIndex < 0 Then
            MsgBox("Please select the car make for this part.")
            Me.cboMakes.Focus()
            Exit Sub
        End If
        If Me.cboModels.SelectedIndex < 0 Then
            MsgBox("The car model is required. " & _
             "It helps to know the specific car this part is made for.")
            Me.cboModels.Focus()
            Exit Sub
        End If
        If Me.txtPartName.Text = "" Then
            MsgBox("You must specify the part name or a (very) short description.")
            Me.txtPartName.Focus()
            Exit Sub
        End If
        If Me.txtUnitPrice.Text = "" Then
            MsgBox("You must enter the price of each unit of this part.")
            Me.txtUnitPrice.Focus()
            Exit Sub
        End If
        If Me.txtPartNumber.Text = "" Then
            MsgBox("Every item of this database must have a number. " & _
             "The number is just a combination of letters and digits." & _
             "Please make up a number and enter it in the Part # box.")
            Me.txtPartNumber.Focus()
            Return
        End If

        ' The part seems to be ready
        ' Get a reference to the root node
        Dim nodNewPart As XmlElement = docXML.CreateElement("Part")
        ' Create a new part as a child of the root (this is a simple node addition
        Dim strNewPart As String = "<PartNumber>" & Me.txtPartNumber.Text & "</PartNumber>" & _
           "<CarYear>" & Me.cboYears.Text & "</CarYear>" & _
           "<Make>" & Me.cboMakes.Text & "</Make>" & _
           "<Model>" & Me.cboModels.Text & "</Model>" & _
           "<PartName Category=""" & Me.cboPartCategories.Text & """>" & _
           Me.txtPartName.Text & "</PartName>" & _
           "<UnitPrice>" & Me.txtUnitPrice.Text & "</UnitPrice>"
        nodNewPart.InnerXml = strNewPart
        docXML.DocumentElement.AppendChild(nodNewPart)
        docXML.Save("Parts.xml")

        ' Reset the form in case the user wants to add another part
        Me.cboYears.SelectedIndex = -1
        Me.cboMakes.SelectedIndex = -1
        Me.cboModels.SelectedIndex = -1
        Me.cboPartCategories.Text = "Miscellaneous"
        Me.txtPartName.Text = ""
        Me.txtUnitPrice.Text = ""

        ' We will generate a random number for the item
        ' To start, we will use the miliseconds as a seed
        Dim tmeNow As DateTime = DateTime.Now
        Dim ms As Integer = tmeNow.Millisecond

        ' Now we can generate a random number between 100000 and 999999
        Dim rndNumber As Random = New Random(ms)

        ' Generate three randomg characters
        Dim firstCharacter As Char = ChrW(rndNumber.Next(65, 90))
        Dim secondCharacter As Char = ChrW(rndNumber.Next(65, 90))
        Dim thirdCharacter As Char = ChrW(rndNumber.Next(65, 90))
        ' Generate a random number made of 4 digits
        Dim numberPart As Integer = rndNumber.Next(1000, 9999)

        ' Exclude the digits 1 and 0 because they create confusion
        If firstCharacter = "I" Or firstCharacter = "O" Then firstCharacter = "A"
        If secondCharacter = "I" Or secondCharacter = "O" Then secondCharacter = "A"
        If thirdCharacter = "I" Or thirdCharacter = "O" Then thirdCharacter = "A"
        ' Generate a random number between 1 and 3
        Dim rndCombination As Integer = rndNumber.Next(1, 4)
        Dim strPartNumber As String = Nothing

        ' Create a part number using some algorithm
        If rndCombination = 1 Then
            strPartNumber = AscW(firstCharacter) & AscW(secondCharacter) & _
             AscW(numberPart) & AscW(thirdCharacter)
        ElseIf rndCombination = 2 Then
            strPartNumber = AscW(firstCharacter) & AscW(numberPart) & _
             AscW(secondCharacter) & AscW(thirdCharacter)
        ElseIf rndCombination = 3 Then
            strPartNumber = AscW(numberPart) & AscW(firstCharacter) & _
             AscW(secondCharacter) & AscW(thirdCharacter)
        Else
            strPartNumber = AscW(rndNumber.Next(100000, 999999))
        End If

        ' Display the new number in the Part # text box
        Me.txtPartNumber.Text = strPartNumber
        Me.cboYears.Focus()

End Sub
  21. Execute the application to test it
  22. Add a few parts as follows (let the computer generate part numbers):
     
    Year Make Model Part Category Part Name Unit Price
    2002 Audi A4 Quattro 1.8L Turbo Exhaust Exhaust Gasket 1.55
    2004 Dodge Neon SE 2.0L L4 Cooling System Radiator Fan Assembly 125.95
    2002 Audi A4 Quattro 1.8L Turbo Drivetrain Axle Differential Bearing - Left 10.25
    2000 Ford Escort 2.0L L4 Ignition Crankshaft Position Sensor 18.65
    2002 Chevrolet Silverado 2500 5.3L V8 Ignition Spark Plugs 1.55
    2004 Dodge Neon SE 2.0L L4 Engine Oil Pump 112.85
    2004 Dodge Neon SE 2.0L L4 Engine Exhaust Valve 5.85
    1986 Acura Integra LS 1.8L L4 Electrical Alternator 110.75
    1998 Toyota Corolla 1.8L L4 Cooling System Radiator 95.95
    2002 Dodge Dakota 3.9L V6 Electrical Starter Motor 145.95
    2004 Honda Civic EX 1.7L L4 Emission Oxygen Sensor 90.55
    2002 Audi A4 Quattro 1.8L Turbo Electrical Alternator 305.50
    2002 Acura NSX 3.0L V6 Engine Oil Filter 7.05
    1998 Jeep Wrangler 2.5L L4 Transfer Case Input Shaft Seal Transfer Case 6.45
    1986 Acura Integra LS 1.8L L4 Fuel/Air Fuel Cap (Regular) 4.15
    2000 Ford Escort 2.0L L4 Brake System Right Caliper Assembly Front 32.85
    2004 Dodge Neon SE 2.0L L4 Clutch Clutch Release Bearing 25.75
    1998 BMW 325I 2.5L L6 Steering Rack and Pinion Bellow Kit 19.25
    2001 Acura Integra GS 1.8L L4 Electrical Voltage Regulator 215.75
    2001 Audi S4 2.7L V6 Engine Timing Belt 35.95
    2002 Audi A4 Quattro 1.8L Turbo Exhaust Muffler Hanger 3.35
    2002 Chevrolet Silverado 2500 5.3L V8 Cooling System Radiator w/Air Tube - w/TOC 215.75
    2002 Acura NSX 3.0L V6 Engine Oil Drain Plug 1.35
    2002 Dodge Dakota 3.9L V6 Electrical Circuit Breaker 3.25
    2004 Dodge Neon SE 2.0L L4 Brake System Brake Pad 20.55
    2004 Honda Civic EX 1.7L L4 Electrical Fusible Link 3.35
    2002 Dodge Dakota 3.9L V6 Electrical Circuit Breaker 3.45
    2004 Honda Civic EX 1.7L L4 Transmission-Manual Differential Bearing 36.75
    1998 Toyota Corolla 1.8L L4 Cooling System Thermostat Standard Temperature 9.35
    2002 Audi A4 Quattro 1.8L Turbo Electrical Cooling Fan Sensor 8.65
    2002 Acura NSX 3.0L V6 Engine Oil Pump Seal 12.55
    2004 Dodge Neon SE 2.0L L4 Brake System Master Cylinder w/o ABS w/2 Wheel 102.95
    2002 Acura NSX 3.0L V6 Engine Valve Stem Oil Seal 1.75
    2002 Dodge Dakota 3.9L V6 Electrical Fuse 0.40
    1998 Toyota Corolla 1.8L L4 Cooling System Regular Thermostat 11.15
  23. Close the forms and return to your programming environmemnt

Order Processing

Order processing consists of receiving requests from a customer and finding the items that the customer wants. To make this easy, as mentioned already, we created a form that allows the user to select the year, the make, the model, and the item"s category. Once these selections are made, a list view displays the items that are available based on these criteria. To select an item and make it part of the order, the user can double-click it in the list view. This action copies the item by its item number, its name, and its unit price. It also sets its quantity to 1. The user can also change the quantity.

The calculations are made automatically so the user doesn"t have to click a button or use a calculator.

Practical Learning Practical Learning: Processing Orders
  1. Display the OrderProcessing form
  2. Double-click the Year combo box and implement its SelectedIndexChanged event as follows:
      
    Private Sub cboYears_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cboYears.SelectedIndexChanged
        Dim strYearSelected As String = Me.cboYears.Text
        Dim strMake As String = Nothing
        Dim docXML As XmlDocument = New XmlDocument

        Text = strYearSelected
        ' Open the Parts.xml file
        docXML.Load("Parts.xml")

        ' We will empty the Make combo box to add a new list
        Me.cboMakes.Items.Clear()
        ' We will empty the Model combo box because the car is about to be changed
        Me.cboModels.Items.Clear()
        ' Also empty the list of available parts
        Me.lvwAvailableParts.Items.Clear()

        ' Create a list of the nodes whose names are CarYear
        Dim nodYears As XmlNodeList = docXML.GetElementsByTagName("CarYear")
        ' Create a list of the nodes whose names are Make
        Dim nodMakes As XmlNodeList = docXML.GetElementsByTagName("Make")

        ' Check every CarYear node to see if its 
        ' value matches the selected year
        Dim i As Integer
        For i = 0 To nodYears.Count - 1 Step 1

            ' If the CarYear of the current node is the same as the
            ' selected year, add its corresponding make to the Make combo box
            If nodYears.ItemOf(i).InnerXml = strYearSelected Then
                strMake = nodMakes.ItemOf(i).InnerText
                ' Before adding the Make to the list, make sure that it doesn"t
                ' exist already in the combo box
                If Not Me.cboMakes.Items.Contains(strMake) Then
                    Me.cboMakes.Items.Add(strMake)
                End If
            End If
        Next
End Sub
  3. In the Class Name combo box, select cboMakes
  4. In the Method Name combo box, select SelectedIndexChanged and implement its event as follows:
      
    Private Sub cboMakes_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles cboMakes.SelectedIndexChanged
        ' Get the year that was selected
        Dim strYearSelected As String = Me.cboYears.Text
        ' Get the make that is selected
        Dim strMakeSelected As String = Me.cboMakes.Text
        ' We will need a model string
        Dim strModel As String = Nothing
        ' We will use a reference to the XML document
        Dim docXML As XmlDocument = New XmlDocument

        ' Open the Parts.xml file
        docXML.Load("Parts.xml")

        ' We will empty the Model combo box to add a new list
        Me.cboModels.Items.Clear()
        ' Also empty the list of available parts
        Me.lvwAvailableParts.Items.Clear()

        ' Create a list of the nodes we will need to locate
        Dim nodYears As XmlNodeList = docXML.GetElementsByTagName("CarYear")
        Dim nodMakes As XmlNodeList = docXML.GetElementsByTagName("Make")
        Dim nodModels As XmlNodeList = docXML.GetElementsByTagName("Model")

        ' Check every CarYear node to see if its 
        ' value matches the selected year
        Dim i As Integer
        For i = 0 To nodYears.Count - 1 Step 1
            ' If the CarYear of the current node is the same as the
            ' selected year, check its corresponding make to see whether
            ' it matches the selected Make
            ' If both the year and the make selected match, then add the
            ' corresponding model to the Model combo box
            If (nodYears.ItemOf(i).InnerXml = strYearSelected) And _
             (nodMakes.ItemOf(i).InnerXml = strMakeSelected) Then
                strModel = nodModels.ItemOf(i).InnerText
                ' Before adding the model to the Model combo box, make sure 
                ' that it doesn"t exist already in the list
                If Me.cboModels.Items.Contains(strModel) Then
                    Exit Sub
                Else ' If it doesn't, then add it
                    Me.cboModels.Items.Add(strModel)
                End If
            End If
        Next
End Sub
  5. In the Class Name combo box, select cboModels
  6. Implement its SelectedIndexChanged event as follows:
      
    Private Sub cboModels_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles cboModels.SelectedIndexChanged
        ' Get the year that was selected
        Dim strYearSelected As String = Me.cboYears.Text
        ' Get the make that is selected
        Dim strMakeSelected As String = Me.cboMakes.Text
        ' We will need a model string
        Dim strModelSelected As String = Me.cboModels.Text

        ' We will use a reference to the XML document
        Dim docXML As XmlDocument = New XmlDocument
        ' Open the Parts.xml file
        docXML.Load("Parts.xml")

        ' Empty the Category combo box
        Me.cboCategories.Items.Clear()
        ' Empty the list of available parts
        Me.lvwAvailableParts.Items.Clear()

        ' Create a list of the nodes we will need to locate
        Dim nodYears As XmlNodeList = docXML.GetElementsByTagName("CarYear")
        Dim nodMakes As XmlNodeList = docXML.GetElementsByTagName("Make")
        Dim nodModels As XmlNodeList = docXML.GetElementsByTagName("Model")
        Dim nodPartNames As XmlNodeList = docXML.GetElementsByTagName("PartName")

        ' Check every CarYear node to see if its 
        ' value matches the selected year
        Dim i As Integer
        For i = 0 To nodYears.Count - 1 Step 1
            ' If the CarYear of the current node is the same as the
            ' selected year, check its corresponding make and model to see whether
            ' they match the selected Make and Model
            If (nodYears.ItemOf(i).InnerXml = strYearSelected) And _
             (nodMakes.ItemOf(i).InnerXml = strMakeSelected) And _
             (nodModels.ItemOf(i).InnerXml = strModelSelected) Then
                ' If you find a part that match the year, the make and the model selected,
                ' then retrieve the (first/only) attribute of the Part Name element
                Dim nodCategory As XmlAttribute = nodPartNames.ItemOf(i).Attributes("Category")
                ' Add the category to the Categories combo box
                Dim strCategory As String = nodCategory.InnerText
                ' Before adding the model to the Model combo box, make sure 
                ' that it doesn"t exist already in the list
                If Me.cboCategories.Items.Contains(strCategory) Then
                    Exit Sub
                Else ' If it doesn't, then add it
                    Me.cboCategories.Items.Add(strCategory)
                End If
            End If
        Next
End Sub
  7. In the Class Name combo box, select cboCategories
  8. In the Method Name combo box, select SelectedIndexChanged and implement its event as follows:
      
    Private Sub cboCategories_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles cboCategories.SelectedIndexChanged
        ' Get the values the user has selected
        Dim strYearSelected As String = Me.cboYears.Text
        Dim strMakeSelected As String = Me.cboMakes.Text
        Dim strModelSelected As String = Me.cboModels.Text
        Dim strCategorySelected As String = Me.cboCategories.Text

        ' Open the Parts.xml file
        Dim docXML As XmlDocument = New XmlDocument
        docXML.Load("Parts.xml")

        ' Empty the list of available parts
        Me.lvwAvailableParts.Items.Clear()

        ' Create a list of the nodes we will need to locate
        Dim nodYears As XmlNodeList = docXML.GetElementsByTagName("CarYear")
        Dim nodMakes As XmlNodeList = docXML.GetElementsByTagName("Make")
        Dim nodModels As XmlNodeList = docXML.GetElementsByTagName("Model")
        Dim nodPartNbr As XmlNodeList = docXML.GetElementsByTagName("PartNumber")
        Dim nodPartNames As XmlNodeList = docXML.GetElementsByTagName("PartName")
        Dim nodPrices As XmlNodeList = docXML.GetElementsByTagName("UnitPrice")

        ' Check every CarYear node to see if its 
        ' value matches the selected year
        Dim i As Integer
        For i = 0 To nodYears.Count - 1 Step 1
            Dim nodCategory As XmlAttribute = nodPartNames.ItemOf(i).Attributes.ItemOf("Category")
            ' Find the year, make, model, and category that match the selected
            If (nodYears.ItemOf(i).InnerXml = strYearSelected) And _
             (nodMakes.ItemOf(i).InnerXml = strMakeSelected) And _
             (nodModels.ItemOf(i).InnerXml = strModelSelected) And _
             (nodCategory.InnerText = strCategorySelected) Then
                ' Create a list view item of the part of the current model
                Dim itmPart As ListViewItem = New ListViewItem(nodPartNbr.ItemOf(i).InnerText, 0)
                itmPart.SubItems.Add(nodPartNames.ItemOf(i).InnerText)
                itmPart.SubItems.Add(nodPrices.ItemOf(i).InnerText)
                ' And display that list to the list view control
                Me.lvwAvailableParts.Items.Add(itmPart)
            End If
        Next
End Sub
  9. After the previous End Sub line, implement the following procedure:
      
    Private Sub CalculateTotalOrder()
        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
        subTotal1 = CDbl(Me.txtSubTotal1.Text)
        subTotal2 = CDbl(Me.txtSubTotal2.Text)
        subTotal3 = CDbl(Me.txtSubTotal3.Text)
        subTotal4 = CDbl(Me.txtSubTotal4.Text)
        subTotal5 = CDbl(Me.txtSubTotal5.Text)
        subTotal6 = CDbl(Me.txtSubTotal6.Text)

        ' Calculate the total value of the sub totals
        orderTotal = subTotal1 + subTotal2 + subTotal3 + _
               subTotal4 + subTotal5 + subTotal6

        ' Display the total order in the appropriate text box
        Me.txtTotalOrder.Text = orderTotal.ToString("F")
End Sub
  10. In the Class Name combo box, select lvwAvailableParts
  11. In the Method Name combo box, select DoubleClick
  12. Implement the event as follows:
      
    Private Sub lvwAvailableParts_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles lvwAvailableParts.DoubleClick
        Dim itmSelectedPart As ListViewItem = Me.lvwAvailableParts.SelectedItems.Item(0)

        ' Check if the first empty row in the Order Processing section
        ' and fill it up with the newly selected item
        If Me.txtPartNumber1.Text = "" Then
            Me.txtPartNumber1.Text = itmSelectedPart.Text
            Me.txtPartName1.Text = itmSelectedPart.SubItems(1).Text
            Me.txtUnitPrice1.Text = itmSelectedPart.SubItems(2).Text
            Me.txtQuantity1.Text = "1"
            Me.txtSubTotal1.Text = itmSelectedPart.SubItems(2).Text
            Me.chkKeepRemove1.Enabled = True
            Me.chkKeepRemove1.Checked = True
            Me.txtQuantity1.Focus()
        ElseIf Me.txtPartNumber2.Text = "" Then
            Me.txtPartNumber2.Text = itmSelectedPart.Text
            Me.txtPartName2.Text = itmSelectedPart.SubItems(1).Text
            Me.txtUnitPrice2.Text = itmSelectedPart.SubItems(2).Text
            Me.txtQuantity2.Text = "1"
            Me.txtSubTotal2.Text = itmSelectedPart.SubItems(2).Text
            Me.chkKeepRemove2.Enabled = True
            Me.chkKeepRemove2.Checked = True
            Me.txtQuantity2.Focus()
        ElseIf Me.txtPartNumber3.Text = "" Then
            Me.txtPartNumber3.Text = itmSelectedPart.Text
            Me.txtPartName3.Text = itmSelectedPart.SubItems(1).Text
            Me.txtUnitPrice3.Text = itmSelectedPart.SubItems(2).Text
            Me.txtQuantity3.Text = "1"
            Me.txtSubTotal3.Text = itmSelectedPart.SubItems(2).Text
            Me.chkKeepRemove3.Enabled = True
            Me.chkKeepRemove3.Checked = True
            Me.txtQuantity3.Focus()
        ElseIf Me.txtPartNumber4.Text = "" Then
            Me.txtPartNumber4.Text = itmSelectedPart.Text
            Me.txtPartName4.Text = itmSelectedPart.SubItems(1).Text
            Me.txtUnitPrice4.Text = itmSelectedPart.SubItems(2).Text
            Me.txtQuantity4.Text = "1"
            Me.txtSubTotal4.Text = itmSelectedPart.SubItems(2).Text
            Me.chkKeepRemove4.Enabled = True
            Me.chkKeepRemove4.Checked = True
            Me.txtQuantity4.Focus()
        ElseIf Me.txtPartNumber5.Text = "" Then
            Me.txtPartNumber5.Text = itmSelectedPart.Text
            Me.txtPartName5.Text = itmSelectedPart.SubItems(1).Text
            Me.txtUnitPrice5.Text = itmSelectedPart.SubItems(2).Text
            Me.txtQuantity5.Text = "1"
            Me.txtSubTotal5.Text = itmSelectedPart.SubItems(2).Text
            Me.chkKeepRemove5.Enabled = True
            Me.chkKeepRemove5.Checked = True
            Me.txtQuantity5.Focus()
        ElseIf Me.txtPartNumber6.Text = "" Then
            Me.txtPartNumber6.Text = itmSelectedPart.Text
            Me.txtPartName6.Text = itmSelectedPart.SubItems(1).Text
            Me.txtUnitPrice6.Text = itmSelectedPart.SubItems(2).Text
            Me.txtQuantity6.Text = "1"
            Me.txtSubTotal6.Text = itmSelectedPart.SubItems(2).Text
            Me.chkKeepRemove6.Enabled = True
            Me.chkKeepRemove6.Checked = True
            Me.txtQuantity6.Focus()
        Else
            Exit Sub
        End If

        ' Calculate the current total order and update the order
        CalculateTotalOrder()
End Sub
  13. In the Class Name combo box, select txtQuantity1
  14. In the Method Name combo box, select Leave and implement its event as follows:
      
    Private Sub txtQuantity1_Leave(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtQuantity1.Leave
        Dim qty As Integer = 0
        Dim unitPrice As Double = 0.0
        Dim subTotal As Double = 0.0

        Try
            ' Get the quantity of the current item
            qty = CInt(Me.txtQuantity1.Text)
        Catch ex As FormatException
            MsgBox("The value you provided for the quantity of the item is invalid" & _
            vbCrLf & "Please try again")
        End Try

        Try
            ' Get the unit price of the current item
            unitPrice = CDbl(Me.txtUnitPrice1.Text)
        Catch ex As FormatException
            MsgBox("The unit price you provided for item is invalid" & _
            vbCrLf & "Please try again")
        End Try

        ' Calculate the current sub total
        subTotal = qty * unitPrice

        ' Display the new sub total in the corresponding text box
        Me.txtSubTotal1.Text = subTotal.ToString("F")
        ' Update the order
        CalculateTotalOrder()
End Sub
  15. In the Class Name combo box, select txtQuantity2
  16. In the Method Name combo box, select Leave and implement its event as follows:
      
    Private Sub txtQuantity2_Leave(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtQuantity2.Leave
        Dim qty As Integer = 0
        Dim unitPrice As Double = 0.0
        Dim subTotal As Double = 0.0

        Try
            qty = CInt(Me.txtQuantity2.Text)
        Catch ex As FormatException
            MsgBox("The value you provided for the quantity of the item is invalid" & _
             vbCrLf & "Please try again")
        End Try

        Try
            unitPrice = CDbl(Me.txtUnitPrice2.Text)
        Catch ex As FormatException
            MsgBox("The unit price you provided for item is invalid" & _
            vbCrLf & "Please try again")
        End Try
        subTotal = qty * unitPrice

        Me.txtSubTotal2.Text = subTotal.ToString("F")
        CalculateTotalOrder()
    End Sub
  17. In the Class Name combo box, select txtQuantity3
  18. In the Method Name combo box, select Leave and implement its event as follows:
      
    Private Sub txtQuantity3_Leave(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtQuantity3.Leave
        Dim qty As Integer = 0
        Dim unitPrice As Double = 0.0
        Dim subTotal As Double = 0.0

        Try
            qty = CInt(Me.txtQuantity3.Text)
        Catch ex As FormatException
            MsgBox("The value you provided for the quantity of the item is invalid" & _
             vbCrLf & "Please try again")
        End Try

        Try
            unitPrice = CDbl(Me.txtUnitPrice3.Text)
        Catch ex As FormatException
            MsgBox("The unit price you provided for item is invalid" & _
             vbCrLf & "Please try again")
        End Try

        subTotal = qty * unitPrice

        Me.txtSubTotal3.Text = subTotal.ToString("F")
        CalculateTotalOrder()
    End Sub
  19. In the Class Name combo box, select txtQuantity4
  20. In the Method Name combo box, select Leave and implement its event as follows:
      
    Private Sub txtQuantity4_Leave(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtQuantity4.Leave
        Dim qty As Integer = 0
        Dim unitPrice As Decimal = 0.0
        Dim subTotal As Double = 0.0

        Try
            qty = CInt(Me.txtQuantity4.Text)
        Catch ex As FormatException
            MsgBox("The value you provided for the quantity of the item is invalid" & _
             vbCrLf & "Please try again")
        End Try

        Try
            unitPrice = CDbl(Me.txtUnitPrice4.Text)
        Catch ex As FormatException

            MsgBox("The unit price you provided for item is invalid" & _
             vbCrLf & "Please try again")
        End Try

        subTotal = qty * unitPrice

        Me.txtSubTotal4.Text = subTotal.ToString("F")
        CalculateTotalOrder()
    End Sub
  21. In the Class Name combo box, select txtQuantity5
  22. In the Method Name combo box, select Leave and implement its event as follows:
      
    Private Sub txtQuantity5_Leave(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtQuantity5.Leave
        Dim qty As Integer = 0
        Dim unitPrice As Decimal = 0.0
        Dim subTotal As Double = 0.0

        Try
            qty = CInt(Me.txtQuantity5.Text)
        Catch ex As FormatException
            MsgBox("The value you provided for the quantity of the item is invalid" & _
             vbCrLf & "Please try again")
        End Try

        Try
            unitPrice = CDbl(Me.txtUnitPrice5.Text)
        Catch ex As FormatException
            MsgBox("The unit price you provided for item is invalid" & _
             vbCrLf & "Please try again")
        End Try

        subTotal = qty * unitPrice

        Me.txtSubTotal5.Text = subTotal.ToString("F")
        CalculateTotalOrder()
    End Sub
  23. In the Class Name combo box, select txtQuantity6
  24. In the Method Name combo box, select Leave and implement its event as follows:
      
    Private Sub txtQuantity6_Leave(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtQuantity6.Leave
        Dim qty As Integer = 0
        Dim unitPrice As Decimal = 0.0
        Dim subTotal As Double = 0.0

        Try
            qty = CInt(Me.txtQuantity6.Text)
        Catch ex As FormatException

            MsgBox("The value you provided for the quantity of the item is invalid" & _
              vbCrLf & "Please try again")
        End Try

        Try
            unitPrice = CDbl(Me.txtUnitPrice6.Text)
        Catch ex As FormatException
            MsgBox("The unit price you provided for item is invalid" & _
             vbCrLf & "Please try again")
        End Try

        subTotal = qty * unitPrice

        Me.txtSubTotal6.Text = subTotal.ToString("F")
        CalculateTotalOrder()
End Sub
  25. In the Class Name combo box, select chkKeepRemove1
  26. In the Method Name combo box, select CheckedChanged and implement its event as follows:
      
    Private Sub chkKeepRemove1_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkKeepRemove1.CheckedChanged
        ' If the check box was unchecked
        If Me.chkKeepRemove1.Checked = False Then
            ' Reset the controls of the current item
            Me.txtPartNumber1.Text = ""
            Me.txtPartName1.Text = ""
            Me.txtUnitPrice1.Text = ""
            Me.txtQuantity1.Text = "0"
            Me.txtSubTotal1.Text = "0.00"
            Me.chkKeepRemove1.Checked = False
            Me.chkKeepRemove1.Enabled = False
            ' Re-calculate the total order to update it
            CalculateTotalOrder()
        End If
    End Sub
  27. In the Class Name combo box, select chkKeepRemove2
  28. In the Method Name combo box, select CheckedChanged and implement its event as follows:
      
    Private Sub chkKeepRemove2_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkKeepRemove2.CheckedChanged
        ' If the check box was unchecked
        If Me.chkKeepRemove2.Checked = False Then
            ' Reset the controls of the current item
            Me.txtPartNumber2.Text = ""
            Me.txtPartName2.Text = ""
            Me.txtUnitPrice2.Text = ""
            Me.txtQuantity2.Text = "0"
            Me.txtSubTotal2.Text = "0.00"
            Me.chkKeepRemove2.Checked = False
            Me.chkKeepRemove2.Enabled = False
            ' Re-calculate the total order to update it
            CalculateTotalOrder()
        End If
End Sub
  29. In the Class Name combo box, select chkKeepRemove3
  30. In the Method Name combo box, select CheckedChanged and implement its event as follows:
      
    Private Sub chkKeepRemove3_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkKeepRemove3.CheckedChanged
        ' If the check box was unchecked
        If Me.chkKeepRemove3.Checked = False Then
            ' Reset the controls of the current item
            Me.txtPartNumber3.Text = ""
            Me.txtPartName3.Text = ""
            Me.txtUnitPrice3.Text = ""
            Me.txtQuantity3.Text = "0"
            Me.txtSubTotal3.Text = "0.00"
            Me.chkKeepRemove3.Checked = False
            Me.chkKeepRemove3.Enabled = False
            ' Re-calculate the total order to update it
            CalculateTotalOrder()
        End If
End Sub
  31. In the Class Name combo box, select chkKeepRemove4
  32. In the Method Name combo box, select CheckedChanged and implement its event as follows:
      
    Private Sub chkKeepRemove4_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkKeepRemove4.CheckedChanged
        ' If the check box was unchecked
        If Me.chkKeepRemove4.Checked = False Then
            ' Reset the controls of the current item
            Me.txtPartNumber4.Text = ""
            Me.txtPartName4.Text = ""
            Me.txtUnitPrice4.Text = ""
            Me.txtQuantity4.Text = "0"
            Me.txtSubTotal4.Text = "0.00"
            Me.chkKeepRemove4.Checked = False
            Me.chkKeepRemove4.Enabled = False
            ' Re-calculate the total order to update it
            CalculateTotalOrder()
        End If
End Sub
  33. In the Class Name combo box, select chkKeepRemove5
  34. In the Method Name combo box, select CheckedChanged and implement its event as follows:
      
    Private Sub chkKeepRemove5_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkKeepRemove5.CheckedChanged
        ' If the check box was unchecked
        If Me.chkKeepRemove5.Checked = False Then
            ' Reset the controls of the current item
            Me.txtPartNumber5.Text = ""
            Me.txtPartName5.Text = ""
            Me.txtUnitPrice5.Text = ""
            Me.txtQuantity5.Text = "0"
            Me.txtSubTotal5.Text = "0.00"
            Me.chkKeepRemove5.Checked = False
            Me.chkKeepRemove5.Enabled = False
            ' Re-calculate the total order to update it
            CalculateTotalOrder()
        End If
End Sub
  35. In the Class Name combo box, select chkKeepRemove6
  36. In the Method Name combo box, select CheckedChanged and implement its event as follows:
      
    Private Sub chkKeepRemove6_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkKeepRemove6.CheckedChanged
        ' If the check box was unchecked
        If Me.chkKeepRemove6.Checked = False Then
            ' Reset the controls of the current item
            Me.txtPartNumber6.Text = ""
            Me.txtPartName6.Text = ""
            Me.txtUnitPrice6.Text = ""
            Me.txtQuantity6.Text = "0"
            Me.txtSubTotal6.Text = "0.00"
            Me.chkKeepRemove6.Checked = False
            Me.chkKeepRemove6.Enabled = False
            ' Re-calculate the total order to update it
            CalculateTotalOrder()
        End If
End Sub
  37. Execute the application to test it
 

Saving an Order

When a order has been placed and it is ready, the user can save it to a file. The orders for each day are stored in their own file so the management can review daily sales. This can be done automatically. If not, the user can save each order in its own file or in any existing file.

Practical Learning Practical Learning: Saving an Order
  1. Display the Order Processing form and double-click the Save button
  2. Implement its Click event as follows:
      
    Private Sub btnSave_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSave.Click
        Dim strFilename As String = Me.dtpFilename.Text & ".xml"
        Dim docXML As XmlDocument = New XmlDocument
        Dim strContent As String = Nothing
        Dim strTotalOrder As String = Me.txtTotalOrder.Text
        Dim strParentOrder As String = Nothing

        If Me.chkKeepRemove1.Checked = True Then
            strContent = strContent & _
             "<PartSold><PartNumber>" & Me.txtPartNumber1.Text & "</PartNumber>" & _
             "<PartName>" & Me.txtPartName1.Text & "</PartName>" & _
             "<UnitPrice>" & Me.txtUnitPrice1.Text & "</UnitPrice>" & _
             "<Qty>" & Me.txtQuantity1.Text & "</Qty>" & _
             "<SubTotal>" & Me.txtSubTotal1.Text & "</SubTotal></PartSold>"
        End If

        If Me.chkKeepRemove2.Checked = True Then
            strContent = strContent & _
             "<PartSold><PartNumber>" & Me.txtPartNumber2.Text & "</PartNumber>" & _
             "<PartName>" & Me.txtPartName2.Text & "</PartName>" & _
             "<UnitPrice>" & Me.txtUnitPrice2.Text & "</UnitPrice>" & _
             "<Qty>" & Me.txtQuantity2.Text & "</Qty>" & _
             "<SubTotal>" & Me.txtSubTotal2.Text & "</SubTotal></PartSold>"
        End If

        If Me.chkKeepRemove3.Checked = True Then
            strContent = strContent & _
             "<PartSold><PartNumber>" & Me.txtPartNumber3.Text & "</PartNumber>" & _
             "<PartName>" & Me.txtPartName3.Text & "</PartName>" & _
             "<UnitPrice>" & Me.txtUnitPrice3.Text & "</UnitPrice>" & _
             "<Qty>" & Me.txtQuantity3.Text & "</Qty>" & _
             "<SubTotal>" & Me.txtSubTotal3.Text & "</SubTotal></PartSold>"
        End If

        If Me.chkKeepRemove4.Checked = True Then
            strContent = strContent & _
             "<PartSold><PartNumber>" & Me.txtPartNumber4.Text & "</PartNumber>" & _
             "<PartName>" & Me.txtPartName4.Text & "</PartName>" & _
             "<UnitPrice>" & Me.txtUnitPrice4.Text & "</UnitPrice>" & _
             "<Qty>" & Me.txtQuantity4.Text & "</Qty>" & _
             "<SubTotal>" & Me.txtSubTotal4.Text & "</SubTotal></PartSold>"
        End If

        If Me.chkKeepRemove5.Checked = True Then
            strContent = strContent & _
             "<PartSold><PartNumber>" & Me.txtPartNumber5.Text & "</PartNumber>" & _
             "<PartName>" & Me.txtPartName5.Text & "</PartName>" & _
             "<UnitPrice>" & Me.txtUnitPrice5.Text & "</UnitPrice>" & _
             "<Qty>" & Me.txtQuantity5.Text & "</Qty>" & _
             "<SubTotal>" & Me.txtSubTotal5.Text & "</SubTotal></PartSold>"
        End If

        If Me.chkKeepRemove6.Checked = True Then
            strContent = strContent & _
             "<PartSold><PartNumber>" & Me.txtPartNumber6.Text & "</PartNumber>" & _
             "<PartName>" & Me.txtPartName6.Text & "</PartName>" & _
             "<UnitPrice>" & Me.txtUnitPrice6.Text & "</UnitPrice>" & _
             "<Qty>" & Me.txtQuantity6.Text & "</Qty>" & _
             "<SubTotal>" & Me.txtSubTotal6.Text & "</SubTotal></PartSold>"
        End If

        If File.Exists(strFilename) Then
            ' If the file exists already, open it
            docXML.Load(strFilename)
            ' Get a reference to the root element
            Dim elmRoot As XmlElement = docXML.DocumentElement
            ' Get a reference to the last child of the root
            Dim nodLastOrder As XmlNode = elmRoot.LastChild
            ' Get the OrderNumber attribute of the last order and increment it by 1
            Dim NewOrderNumber As Integer = CInt(nodLastOrder.Attributes.ItemOf("OrderNumber").InnerText) + 1

            ' Create a new order as an element
            Dim elmNewOrder As XmlElement = docXML.CreateElement("Order")
            ' Add its attributes
            elmNewOrder.SetAttribute("OrderNumber", CStr(NewOrderNumber.ToString()))
            elmNewOrder.SetAttribute("TotalOrder", strTotalOrder)
            elmNewOrder.InnerXml = strContent
            docXML.DocumentElement.AppendChild(elmNewOrder)
            docXML.Save(strFilename)
        Else

            ' If the file doesn"t exist, get ready to create it
            strParentOrder = "<Order OrderNumber=""1"" TotalOrder=""" & strTotalOrder & "" > ")"

            ' If the file doesn"t exist, create it
            docXML.LoadXml("<?xml version=""1.0"" encoding=""utf-8""?>" + _
             "<Orders>" & _
             strParentOrder & strContent & "</Order></Orders>")
            docXML.Save(strFilename)
        End If

        ' Reset the Order Processing form
        Me.lvwAvailableParts.Items.Clear()
        Me.cboCategories.SelectedIndex = -1
        Me.cboModels.SelectedIndex = -1
        Me.cboMakes.SelectedIndex = -1
        Me.cboYears.SelectedIndex = -1
        Me.chkKeepRemove1.Checked = False
        Me.chkKeepRemove2.Checked = False
        Me.chkKeepRemove3.Checked = False
        Me.chkKeepRemove4.Checked = False
        Me.chkKeepRemove5.Checked = False
        Me.chkKeepRemove6.Checked = False
        Me.CalculateTotalOrder()
End Sub
  3. Execute the application
  4. To simulate some sales, create the following orders
     
    First Order - Date Saved: 16 June 1998
    Year Make Model Category Item Name Qty
    1986 Acura Integra LS 1.8L L4 Electrical Alternator 1
    1986 Acura Integra LS 1.8L L4 Fuel/Air Fuel Cap (Regular) 4
    Second Order - Date Saved: 24 August 2000
    1998 Toyota Corolla 1.8L L4 Cooling System Radiator 2
    1998 Jeep Wrangler 2.5L L4 Transfer Case Input Shaft Seal Transfer Case 4
    Third Order - Date Saved: 16 June 1998
    2002 Chevrolet Silverado 2500 5.3L V8 Ignition Spark Plugs 4
    2002 Dodge Dakota 3.9L V6 Electrical Starter Motor 1
    2002 Acura NSX 3.0L V6 Engine Oil Filter 2
    1998 BMW 325I 2.5L L6 Steering Rack and Pinion Bellow Kit 2
    Fourth Order - Date Saved: 24 August 2000
    2000 Ford Escort 2.0L L4 Ignition Crankshaft Position Sensor 2
    2000 Ford Escort 2.0L L4 Brake System Right Caliper Assembly Front 1
    Fifth Order - Date Saved: 21 January 2005
    2004 Dodge Neon SE 2.0L L4 Engine Oil Pump 1
    2004 Dodge Neon SE 2.0L L4 Clutch Clutch Release Bearing 2
    2004 Dodge Neon SE 2.0L L4 Cooling System Radiator Fan Assembly 1
     
    College Park Auto-Parts - Order Processing
  5. Close the forms
  6. Preview the saved orders in your browser
     
  7. Return to your programming environment
 
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