Microsoft Visual Basic: Details on Controls Properties

	Details on Controls Properties

The Size of a Control

The Size Structure

To represent the size of something, the System.Drawing namespace defines the Size structure that is equipped with two main properties. There are four characteristics that define a Size value: its location and its dimensions. A Size value must have a starting point (X, Y) just as the Point object was illustrated earlier. The Width is the distance from the left to the right borders of a Size value. The Height property represents the distance from the top to the bottom borders of a Size value:

Based on this, to create a Size object, if you know only its location (X and Y), you can use the following constructor:

Public Sub New (pt As Point)

After declaring a variable with this constructor, you can access its Width and Height properties to complete the definition of the Size object. If you already have the location of a Size object by other means, you may not be interested in (re)defining its location. In this case, you may only want to specify the dimensions of the variable. To do this, you can use the following constructor:

Public Sub New(width As Integer, height As Integer)

Besides Size, the System.Drawing namespace also provides the SizeF structure. It uses the same properties as Size except that its members float values.

The Rectangle Structure

A rectangle is a geometric figure that has four sides. To support this figure, the System.Drawing namespace provides the Rectangle and the RectangleF structures. A rectangle can be represented as follows:

Like every geometric representation in your program, a rectangular figure is based on a coordinate system whose origin is located on a top-left corner. The object that "owns" or defines the rectangle also owns this origin. For example, if the rectangle belongs to a control that is positioned on a form, then the origin is on the top-left corner just under the title bar of the form, provided the form has a title bar.

To completely represent it, a rectangle is defined by its location and its dimensions. The location is defined by a point on the top-left corner of the rectangle. The distance from the left border of the object that owns the rectangle to the left border of the rectangle is represented by a property called Left. The distance from the top border of the object that owns the rectangle to the top border of the rectangle is represented by a property called Top. The distance from the left to the right borders of the rectangle is represented by a property called Width. The distance from the left to the right borders of the rectangle is represented by a property called Height. The distance from the left border of the object that owns the rectangle to the right border of the rectangle is represented by a property called Right. The distance from the top border of the object that owns the rectangle to the bottom border of the rectangle is represented by a property called Bottom. Based on this, a rectangle can be illustrated as follows:

To create a rectangle, you must provide at least its location and dimensions. The location can be represented by a Point value and the dimensions can be represented with a Size value. Based on this, you can use the following constructor to declare a Rectangle variable:

Public Sub New(location As Point, size As Size)

This constructor requires that you define a Point and a Size in order to use it. If instead you know the integer values of the location and dimensions, you can use the following constructor to declare a Rectangle object:

Public Sub New(x As Integer, y As Integer, width As Integer, height As Integer)

At any time, you can access or retrieve the characteristics of a Rectangle object as illustrated in the above picture from its properties. You use the same names we used in the picture.

Besides the Rectangle structure, the System::Drawing namespace provides the RectangleF structure that uses the same definition as Rectangle, except that it is defined with float values instead of integers.

Introduction to the Width and Height of a Control

The distance from the left border to the right border of a control is referred to as its width property. In the same way, the distance from the top to the bottom borders of a control is its height value. This can be illustrated as follows:

The combination of the width and the height of a control is referred to as its size. If you add a control to a form, it assumes a default size.

To specify the size of a control during design, access its Properties window:

Click the Size field and enter two numbers separated by a comma
Alternatively, expand the Size field, click Width and type a value; click Height and type a value

Programmatically Specifying the Size of a Control

To support the size of an object, the System.Drawing namespace defines the Size structure. There are four characteristics that define a Size value: its location and its dimensions. A Size value must have a starting point (X, Y) just as the Point object was illustrated earlier. The width is the distance from the left to the right borders of a Size object. The height represents the distance from the top to the bottom borders of a Size value:

To assist you with sizes, the Size structure provides the following constructor:

Public Sub New(width As Integer, height As Integer)

Using this constructor, to programmatically specify the size of a control, assign a Size value to its Size property. Here is an example:

Imports System
Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class WinControls
        Inherits Form

        Private BtnSubmit As Button

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()
            Dim pt As Point

            BtnSubmit = New Button()
            BtnSubmit.Text = "Submit"
            BtnSubmit.Location = New Point(100, 40)

            BtnSubmit.Size = New Size(80, 32)

            Controls.Add(BtnSubmit)
        End Sub

        Public Shared Function Main() As Integer

            Application.Run(New WinControls())
            Return 0

        End Function

    End Class

End Module

You can also define a Size object using a Point value. To support this, the Size structure is equipped with the following constructor:

Public Sub New(pt As Point)

After declaring a variable with this constructor, you can access its Width and Height properties to complete the definition of the Size object. If you already have the size of an object, you may only want to specify the dimensions of the variable. To do this, you can use the

Besides the Size, the System.Drawing namespace also provides the SizeF structure. It uses the same properties as Size except that its members float types.

To retrieve the dimensions of a control, you can get its Size property and assign it to a Size object.

The Rectangular Location and Size of a Control

The combination of the location and size of an object is represented as a rectangle: a geometric figure with four sides. To support this figure, the System.Drawing namespace provides the Rectangle and the RectangleF structures. A rectangle can be represented as follows:

To create a rectangle, you must provide at least its location and dimensions. The location can be represented by a Point value and the dimensions can be represented with a Size value. Based on this, you can use the following constructor to declare a Rectangle variable:

Public Sub New(location As Point, size As Size)

Public Sub New(x As Integer, y As Integer, width As Integer, height As Integer)

At any time, you can access or retrieve the characteristics of a Rectangle object as illustrated in the above picture from its properties. You use the same names we used in the picture.

Besides the Rectangle structure, the System.Drawing namespace provides the RectangleF structure that uses the same definition as Rectangle, except that it is defined with float values instead of integers.

The be able to recognize the location and the size of a control, the Control class is equipped with a property named Bounds. This property is of type Rectangle represented by the property. Therefore, at any time, to get the location and the size of a control, you can call its Bounds property, which produces a Rectangle value.

Techniques of Visually Resizing a Control

Introduction

All graphical controls, including the form, can be resized using guiding mouse cursors or the keyboard. To resize a control, first select it. Except for the form, whenever a control is selected, there are eight handles around it. To resize the control, position your mouse on one of the handles. The mouse pointer will change, indicating in what direction you can move to resize the control.

Cursor	Role
	Moves the seized border in the North-West <-> South-East direction
	Shrinks or heightens the control
	Moves the seized border in the North-East <-> South-West direction
	Narrows or enlarges the control

Before resizing a control, as mentioned already, first select it. To enlarge a control:

Position the mouse on the right (or the left) handle. Then click and drag in right (or left) direction. Once you get the desired width, release the mouse
Press and hold Shift. Then press the right arrow key as many times as you want. Once you get the desired width, release Shift

To narrow a control:

Position the mouse on its right (or its left) handle. Then click and drag in the left (or the right) direction. Once you get the desired width, release the mouse
Press and hold Shift. Then press the left arrow key as many times as you want. Once you get the desired width, release Shift

To heighten a control:

Position the mouse on its top (or its bottom) handle. Then click and drag in the top (or the bottom) direction. Once you get the desired width, release the mouse
Press and hold Shift. Then press the up arrow key as many times as you want. Once you get the desired width, release Shift

To shrink a control:

Position the mouse on its top (or its bottom) handle. Then click and drag in the bottom (or the top) direction. Once you get the desired width, release the mouse
Press and hold Shift. Then press the down arrow key as many times as you want. Once you get the desired width, release Shift

The Width and Height of a Control

Imagine you have added three controls to your form and, after spending some time designing them, they appear as follows:

The dimensions of the controls are not set professionally. As seen above, you can resize by dragging their borders but this might take a while if you want them to have the same width, the same height, or both the same height and width. The dimensions of a control or a group of controls are carried by a Size value.

At design time, to change the dimensions of a control, first click it. Then, in the Properties window, change the values of its Size property.

To change the dimensions of a group of controls, first select them. Then, in the Properties window, change the values of the Size field. The new value would be applied to all selected controls. Alternatively, the Form Designer provides tools to automatically do this for you.

To synchronize the widths of a group of controls, first select them. Then, on the Layout toolbar or on the Format group of the main menu, select:

Button	Name	Format
	Make Same Width	Make Same Size -> Width

Result: All controls, except for the base control (the control that has the dark handles), will be resized horizontally so they have the same width as the base control:

The top control is used as reference
	=>
The middle control is used as reference
	=>
The bottom control is used as reference

To set the same height to a group of controls, first select them. Then, on the Layout toolbar or on the Format group of the main menu, select:

Button	Name	Format
	Make Same Height	Make Same Size -> Height

Result: All controls, except for the base control (the control that has the dark handles), will be resized vertically so they have the same height as the base control:

The top control is used as reference
	=>
The middle control is used as reference
	=>
The bottom control is used as reference
	=>

To set the same width and the same height to a group of controls, first select them. Then, on the Layout toolbar or on the Format group of the main menu, select:

Button	Name	Format
	Make Same Size	Make Same Size -> Both

Result: The Form Designer will calculate the sum of the heights of all controls and find their average height (AvgHeight). It will also calculate the sum of the widths of all controls and find their average width (AvgWidth). These averages will be applied to the height and the width respectively of each control:

	=>
	=>
	=>

Practical Learning: Setting the Locations and Sizes of Controls

To add a project, on the main menu, click File -> Add -> New Project...
In the middle list, make sure Windows Application.
In the Name box, replace the content with Rectangle2 and press Enter
From the Toolbox and from what we learned in the previous lesson, add four labels, four text boxes, and two buttons to the form
Based on what we have reviewed so far, design the form as follows:
To test the application, in the Solution Explorer, right-click Rectangle2 and click Build
While the form is displaying, drag its right border to widen it. Also drag its bottom border to heighten it
Close the form and return to your programming environment
Save all

Common Properties of Controls

The Content Alignment of a Control

When a control can be resized, or it has been configured to be sizable, as it would be the case for a label or a button, you can specify in what part of its confined borders the text should display. This characteristics is controlled by the TextAlign property. To specify the alignment of text during design, access the Properties window for a control and use the TextAlign field:

Text Alignment

The TextAlign property is of type ContentAlignment, which is an enumeration. The members and result of this enumeration are:

TopLeft	TopCenter	TopRight

MiddleLeft	MiddleCenter	MiddleRight

BottomLeft	BottomCenter	BottomRight

To programmatically specify the text alignment of a control, access its TextAlign property and assign it the desired member of the ContentAlignment enumeration. Here is an example:

Imports System
Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class WinControls
        Inherits Form

        Private BtnSubmit As Button

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()
            BtnSubmit = New Button()
            BtnSubmit.Text = "Submit"
            BtnSubmit.Location = New Point(20, 20)
            BtnSubmit.Size = New Size(100, 60)

            BtnSubmit.TextAlign = ContentAlignment.BottomRight

            Controls.Add(BtnSubmit)
        End Sub

        Public Shared Function Main() As Integer

            Application.Run(New WinControls())
            Return 0

        End Function

    End Class

End Module

Anchoring a Control

If you position a (visual) control on a form and if the control is positioned on the top left section of the form, when the user resizes the form, the control's position would appear static, it would not move. This could be a concern if the control is positioned on the right, the bottom or the lower right sections of the form. When the user resizes the form, the control's position would not be updated. Sometimes you will want the control to have the same location and/or distance with regard to the bottom, the right, and/or the lower right corners of the form.

The ability to manage a control or a group of controls' location and size when the user resizes it is done using the Anchor property:

The Anchor property is created from the AnchorStyles enumeration. By default, when you add a control to a form, its position is relative to the top left corner of its container. You can also set the control's position with regards to its container's right and bottom borders. The Anchor property can be used to "glue" one border of a control to its parent using one of the following values:

Bottom: The control bottom border will be the same even if the parent is heighten or shrunk

Left: The control left border will be the same even if the parent is widened or narrowed

None: No anchoring is applied

Right: The control right border will be the same even if the parent is widened or narrowed

Top: The control top border will be the same even if the parent is heightened or shrunk

In the same way, you can combine AnchorStyles values to "glue" one or more corners of a control to its parent when the parent is resized:

To visually combine two or more AnchorStyles values, after selecting the control(s) on the form, in the Properties window, click the arrow of the Anchor field and click each desired Anchor button
To programmatically combine two or more AnchorStyles values, you use the OR bit operator, which is |

Practical Learning: Anchoring the Controls

On the form, select the buttons on the right side:
In the Properties window, click Anchor and click the arrow of its combo box
Click the top vertical line and the right horizontal line. Click the left horizontal line to clear it:
On the form, select all text boxes
In the Properties window, click Anchor and click the arrow of its combo box. Click the right horizontal line and keep the others
Execute the application
Resize it horizontally and vertically to see the result
Close the form and return to your programming environment

Control Docking

When a control is added to a host, depending on the control, it may be automatically positioned where the mouse landed. In some cases, you will want the control to be attached to a border or to a corner of its parent. This can be done using the Dock property:

This property is managed through the DockStyle enumeration. To use this property, click the control and, in the Properties window, click the arrow of the Dock field. You can then select one of the following values:

Bottom: The control will be attached to the bottom border of its parent:

Fill: The control will use the whole client area of its parent.

Left: The control will be attached to the left border of its parent:

None: The control will be kept where it was positioned on the parent:

Right: The control will be attached to the right border of its parent:

Top: The control will be attached to the top border of its parent:

To programmatically specify the docking option of a control, access its Dock property and assign the desired member of the DockStyle enumeration. Here is an example:

Imports System
Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class WinControls
        Inherits Form

        Private BtnSubmit As Button

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()
            BtnSubmit = New Button()
            BtnSubmit.Text = "Submit"
            BtnSubmit.Location = New Point(20, 20)
            BtnSubmit.Size = New Size(100, 60)

            BtnSubmit.Dock = DockStyle.Right

            Controls.Add(BtnSubmit)
        End Sub

        Public Shared Function Main() As Integer

            Application.Run(New WinControls())
            Return 0

        End Function

    End Class

End Module

This would produce:

Dock

Practical Learning: Docking a Control

On the Toolbox, click Panel
On the form, click and hold the mouse somewhere in the lower-left section. Then drag right and slightly up to draw it as follows (no need for precision):
While the panel control is still selected, in the Properties window, click Dock and click the arrow of its combo box
Select the box above None (to select Bottom)
Save all

Aesthetic Aspects of a Control

Background Color

Controls used on Microsoft Windows are painted using a color known as Control. If you don't like the default color that paints the background of a control, you can access the BackColor field of the Properties window:

You can then select one of the preset colors from 3 windows represented with tabs:

As you can see, the System and the Web tabs provide colors by name. All regular names of colors of the English language are represented. If you have done Windows programming before, you may recognize the names of colors in the System tab because they are the same names you would see in Control Panel, except that the names are in one word. If you have done web development before, you may recognize the names because they are the same defined by Netscape. The names in both the System and the Web tabs are defined in an enumeration called Color.

If you are not familiar with the names of colors, you can visually select a color in the Custom tab.

To programmatically specify the background color of a control, access its BackColor property and assign it the desired member of the Color enumeration. Here is an example:

Imports System
Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class WinControls
        Inherits Form

        Private BtnSubmit As Button

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()
            BtnSubmit = New Button()
            BtnSubmit.Text = "Submit"
            BtnSubmit.Location = New Point(20, 20)
            BtnSubmit.Size = New Size(100, 60)

            BtnSubmit.BackColor = Color.Aquamarine

            Controls.Add(BtnSubmit)
        End Sub

        Public Shared Function Main() As Integer

            Application.Run(New WinControls())
            Return 0

        End Function

    End Class

End Module

Practical Learning: Changing the Background Color of a Control

On the form, click the bottom panel
In the Properties window, click BackColor and click its arrow
Click the Custom tab and click the color at 3rd column - 2nd row:
Execute the application to test it
Close the form and return to your programming environment

Background Image

Instead of a color, you may want to fill the control with a picture. To do this, you can access the control's BackgroundImage property. This provides an ellipsis button you can use to locate and select the desired picture.

Border Style

Some controls display a border when they are drawn and some others don't. Consider the following:

Some of these controls allow you to specify a type of border you want to show surrounding the controls. This characteristic is controlled by the BorderStyle property, which is based on BorderStyle enumerator. Its members are:

Value	Example
Fixed3D
FixedSingle
None

To programmatically specify the border style of a control, access its BorderStyle property and assign it the desired BorderStyle member. Here is an example:

Imports System
Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class WinControls
        Inherits Form

        Private PnlViewer As Panel

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()

            PnlViewer = New Panel()
            PnlViewer.BorderStyle = BorderStyle.Fixed3D
            PnlViewer.BackColor = Color.LightBlue
            Controls.Add(PnlViewer)

        End Sub

        Public Shared Function Main() As Integer

            Application.Run(New WinControls())
            Return 0

        End Function

    End Class

End Module

API Characteristics of Controls

Tab Ordering

A user can navigate through controls using the Tab key. When that key has been pressed, the focus moves from one control to the next. By their designs, not all controls can receive focus and not all controls can participate in tab navigation. Even controls that can receive focus must be primarily included in the tab sequence.

At design time, the participation to tab sequencing is controlled by the Boolean TabStop property in the Properties window. Every visual control that can receive focus is already configured to have this property set to True. If you want to remove a control from this sequence, set its TabStop value to False.

If a control has the TabStop property set to True, to arrange the navigation order of controls, you have two main options. At design time, you can click a control on the form. Then, on the Properties window, change the value of its TabIndex field. The value must be a positive short integer.

The best and easiest way to arrange the tab sequence of controls is to manage it visually. To do this, first display the form. Then, on the main menu, click View. This causes a number to be positioned on every control of the form. Here is an example:

To arrange the sequence any way you like, click each control once in the desired order. Normally, static controls (such as the label, the picture box, the panel, etc) never receive focus when the application is running; therefore, you can skip such controls.

Practical Learning: Setting the Tab Order of Controls

Click anywhere in the form
On the main menu, click View -> Tab Order
On the form, click, in the following order, the text box on the right side of Length, the text box on the right side of Height, the Calculate button, and the Close button
Press Esc to dismiss the Tab Order tool
On the form, click the text box on the right side of Perimeter:
In the Properties window, set the TabStop to False
In the same way, set the TabStop property of the text box on the right side of Area: to False
Execute the application
Press Tab a few times and observe the behavior
Close the form and return to your programming environment

Control's Visibility

A control is referred to as visible if it can be visually located on the screen. A user can use a control only if he or she can see it. As a programmer, you have the role of deciding whether a control must be seen or not and when. The visibility of an object is controlled by the its Visible property. This is a Boolean property.

At design time, when you add a control to a parent, it is visible by default. This is because its Visible property is set to True in the Properties window. In the same way, if you programmatically create a control, by default, it is made visible once you add it to its parent's Controls property.

If you don't want a control to primarily appear when the form comes up, you can either set its Visible property to False or set its parent's visible property to False. Equivalently, at run time, to hide a control, assign a False value to either its Visible property or its parent's Visible property. Keep in mind that when a parent gets hidden, it also hides its children. On the other hand, a parent can be made visible but hide one or some of its children.

To programmatically check whether a control is visible at one time, apply a conditional statement (if or while) to its Visible property and check whether its value is true or false.

Control's Availability

For the user to use a control, it must allow operations on it. For example, if a control is supposed to receive text, the user can enter characters in it only if this is made possible. To make a control available to the user, the object must be enabled. The availability of an object is controlled by the Boolean Enabled property.

By default, after adding a control to a form, it is enabled and its Enabled property in the Properties window is set to True. An enabled control displays its text or other characteristics in their normal settings. If you want to disable a control, set its Enabled property to False. In the following picture, a text box and a button are disabled:

To programmatically find out whether a control is enabled or not, check its Enabled property.

Allowing Drag n' Drop Operations

Drag n' drop is the ability to drag an object or text from one location or object to another. This is a significant operation in computer use. Although Microsoft Windows fully supports drag n' drop operations, because the operating system cannot predict how the operations should be carried, you must write code.

Various controls support drag n' drop operations. While most controls support them, it is not always realistic to implement the operations on every control. This means that you will have to decide when, how, and what controls of your application will need to allow the user do drag what and drop it where.

A control that allows drag n' drop operations is equipped with a Boolean property named AllowDrop. When you set this property to true, it means the user can either drag something from it or drop something on it. After setting this property, you must write code. We will see examples in future lessons.