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Windows Control: The Label

 

Description

A label is a control that serves as a guide to the user. It provides static text that the user cannot change but can read to get information on a form. The programmer can also use it to display simple information to the user. Most controls on the form are not explicit at first glance and the user may not know what they are used for. Therefore, you can assign a label to a control as a help to the user.

     

Creating a Label

To add a label to a container, click the Label button Label from the Toolbox and click the object that would host it.

To programmatically create a label, declare a handle to Label, initialize it using its default constructor, and add it to the Controls property of the form. Here is an example:

Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class Starter
        Inherits Form

        Private lblMessage As Label

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()

            lblMessage = New Label()
            Controls.Add(lblMessage)

        End Sub

    End Class

    Function Main() As Integer

        Dim frmStart As Starter = New Starter

        Application.Run(frmStart)

        Return 0
    End Function

End Module

Practical LearningPractical Learning: Introducing Labels

  1. Start Microsoft Visual Basic and create a Windows Application named ElementaryAddition1
  2. From the Common Control section of the Toolbox, click Label and click the form
  3. From the Common Control section of the Toolbox, click the Label again and click the form
  4. From the Common Control section of the Toolbox, click the Label again and click the form

Characteristics of a Label

 

The Caption

The most important characteristic of a label control is the text it displays. That text is also referred to as its caption and this is what the user would read. The text of a label is its Text property and is its default. To set a label’s caption, after adding the control to a container, click Text in the Properties window and type the desired value. As we mentioned when studying controls characteristics, at design time, the text you type in the Text field is considered “as is”. If you want to create a more elaborate and formatted string, you would have to do it programmatically. Here is an example:

Public Sub InitializeComponent()

            lblMessage = New Label()

            lblMessage.Text = Date.Today.ToLongDateString()

            Controls.Add(lblMessage)

End Sub

Here is an example of what this would produce:

Label's Caption

When it comes to its caption, one of the most valuable characteristics of the text of a label is the variance of the font. When designing a caption. you can change the default font to make it more attractive.

Practical LearningPractical Learning: Captioning the Labels

  1. On the form, click the first label
  2. In the Properties window, click Text and type 00
  3. Click (Name) and type lblOperand1
  4. Click TextAlign and the arrow of its combo box to select Center
  5. Click the + button of the Font field and change the characteristics as follows:
    Name: Tahoma
    Size:   48
    Bold:   True
  6. On the form, click the second label and, in the Properties window, change its characteristics as follows:
    Text: +
    TextAlign: Center
    (Name): lblOPeration
    Font -> Name: Arial
    Font -> Size:   50
    Font -> Bold:   True
  7. On the form, click the third label and, in the Properties window, change its characteristics as follows:
    Text: 00
    TextAlign: Center
    (Name): lblOperand2
    Font -> Name: Arial
    Font -> Size:   50
    Font -> Bold:   True
  8. Save all

Automatically Sizing a Label

After adding a label to a form, by default, it receives a fixed size. If you type its caption and press Enter, the text you provided would be confined to the allocated dimensions of the control. If the text is too long, part of it may disappear. You can then resize the label to provide more area. Another solution is to automatically resize the label to accommodate the length of the string you typed. This is aspects is controlled by the Boolean AutoSize property. Its default value is False. If you set this property to True, at design time, a rectangular border appears around it. If you type a string in the Text field and press Enter, the control would be resized to show the whole string but using only the necessary space.

If you programmatically create a label, it assumes a default size. If you assign it a string that is too long for that default size, part of the string may appear on a subsequent line. If you want the whole string to appear on the same line, you can set the AutoSize to true. Here is an example:

Public Sub InitializeComponent()

            lblMessage = New Label()
            lblMessage.Text = Date.Today.ToLongDateString()

            lblMessage.AutoSize = True

            Controls.Add(lblMessage)

End Sub

Here is an example of what this would produce:

Label Auto Size

Practical LearningPractical Learning: Using AutoSize

  1. Click an unoccupied area of the form and press Ctrl + A to select all three labels
  2. In the Properties window, double-click AutoSize to set the value to False
  3. Save all

Content Alignment

After typing the caption of a label whose AutoSize property is set to False, you can resize its allocated space to your liking. This is because a string occupies a rectangular area. Here is an example:

Content Alignment

By default, the caption of a label is positioned starting on the middle-left side of its allocated rectangle. Alternatively, you can position it to one of the nine available positions. As we saw is Lesson 5, the position of the caption of a label is controlled by the TextAlign property which is based on the ContentAlignment enumerator:

Text Alignment

It can have the following values:

TopLeft TopCenter TopRight
TopLeft TopCenter TopRight
MiddleLeft MiddleCenter MiddleRight
MiddleLeft MiddleCenter MiddleRight
BottomLeft BottomCenter BottomRight
BottomLeft BottomCenter BottomRight

Pictures on a Label

Other fancy characteristics you can apply to a label include its font and color. For example, a label is primarily meant to display a string. To make it fancier, you can display a (small) picture next to it. To do this, at design time, use the Image field of the Properties window to select a picture. You can also specify the picture at run time by assigning an Image value to the Label.Image property. After adding a picture that would accompany the label, you can specify what position the picture would hold with regards to the label. To do this, select the desired position of the ImageAlign field in the Properties window.

Instead of using a picture from the Image property, you can create a list of images using an ImageList control and assign it to the label. In fact, the advantage of an ImageList is that, unlike the Image property, it allows you to use more than one picture.

After assigning an ImageList to the label control using the Properties window or code, you can use the ImageIndex to specify what picture to display next to the label.

A Label's Mnemonic

A label provides another property called UseMnemonic. This property is valuable only when the label accompanies another control.

Practical LearningPractical Learning: Using a Text Box

  1. Complete the design of the form as follows:
     
    Elementary
    Control Text Name TextAlign Font Additional Properties
    Label 00 lblOperand1 Center Name: Tahoma
    Size:   48
    Bold:   True
    ForeColor: Blue
    Label +   Center Name: Arial
    Size:   50
    Bold:   True
    ForeColor: Maroon
    Label 00 lblOperand2 Center Name: Tahoma
    Size:   48
    Bold:   True
    ForeColor: Blue
    Label =   Center Name: Arial
    Size:   50
    Bold:   True
    ForeColor: Green
    Label 00 lblResult Center Name: Tahoma
    Size:   48
    Bold:   True
     
    Label New Operation lblNewOperation Center Name: Tahoma, Size: 28 Bold: True BorderStyle: Fixed3D
    ForeColor: White
    BackColor:Maroon 
    Label Quit lblQuit Center Name: Tahoma, Size: 28 Bold: True BorderStyle: FixedSingle
  2. Double-click New Operation and implement its event as follows:
     
    Private Sub lblNewOperation_Click(ByVal sender As System.Object, _
                                          ByVal e As System.EventArgs) _
                                          Handles lblNewOperation.Click
            Dim Operand1 As Integer
            Dim Operand2 As Integer
            Dim strAnswer As String
            Dim iAnswer As Integer
            Dim rnd As Random = New Random()
    
            Operand1 = rnd.Next(99)
            Operand2 = rnd.Next(99)
            Dim Result As Integer = Operand1 + Operand2
    
            lblOperand1.Text = Operand1.ToString()
            lblOperand2.Text = Operand2.ToString()
            lblResult.Text = "0"
            Dim strPrompt As String = lblOperand1.Text & " + " & _
                                   lblOperand2.Text & " ="
    
            strAnswer = InputBox(strPrompt, "Elementary Addition", "000", 100, 100)
    
            If IsNumeric(strAnswer) Then
    
                iAnswer = CInt(strAnswer)
                lblResult.Text = CStr(iAnswer)
    
                If iAnswer = Result Then
                    MsgBox("WOW - Good Answer")
                Else
                    MsgBox("PSSST - Wrong Answer")
                End If
            Else
                MsgBox("Invalid Numeric Value!")
            End If
            
    End Sub
  3. In the Class Name combo box, select lblQuit
  4. In the Method Name combo box, select Click and implement the event as follows:
     
    Private Sub lblQuit_Click(ByVal sender As Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles lblQuit.Click
            End
    End Sub
  5. Execute the application and test it
     
    Elementary
     
     
     
     
  6. Click the Close button to close the form and return to your programming environment

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