lesson 20 Using Checkbox

In this lesson, we shall learn how to write code for the checkbox. The Checkbox allows the user to select one or more items by checking the check box or check boxes concerned. For example, in the Font dialog box of any Microsoft Text editor like Microsoft Words, there are many checkboxes under the Effects section. The user can choose to underline, subscript, small caps, superscript, blink and more. In Visual Basic 2013, you may create a shopping cart where the user can click on checkboxes that correspond to the items they intend to buy, and the total payment can be computed at the same time.

Example 20.1: Shopping Cart

In this example, we add a few labels, two buttons, and six check boxes. We declare the price of each item using the Const keyword. If a checkbox is being ticked, its state is True else its state is False. To calculate the total amount of purchase, we use the mathematical operator +=. For example, sum+=BN is actually sum=sum+BN. Finally, we use the ToString method to display the amount in currency.

The Code

Public Class Form1
Private Sub BtnCal_Click(sender As Object, e As EventArgs) Handles BtnCal.Click
Const LX As Integer = 100
Const BN As Integer = 500
Const SD As Integer = 200
Const HD As Integer = 80
Const HM As Integer = 300
Const AM As Integer = 150
Dim sum As Integer
 If CheckBox1.Checked = True Then
  sum += LX
 End If

 If CheckBox2.Checked = True Then
  sum += BN
 End If

 If CheckBox3.Checked = True Then
  sum += SD
 End If
 If CheckBox4.Checked = True Then
  sum += HD
 End If

 If CheckBox5.Checked = True Then
  sum += HM
 End If

 If CheckBox6.Checked = True Then
  sum += AM
 End If
  LblTotal.Text = sum.ToString("c")
End Sub

Private Sub BtnReset_Click(sender As Object, e As EventArgs) Handles BtnReset.Click
 CheckBox1.Checked = False
 CheckBox2.Checked = False
 CheckBox3.Checked = False
 CheckBox4.Checked = False
 CheckBox5.Checked = False
 CheckBox6.Checked = False

End Sub
End Class

The Runtime Interface

Here is another example

Example 20.2

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Const large As Integer = 10.0
Const medium As Integer = 8
Const small As Integer = 5
Dim sum As Integer
 If CheckBox1.Checked = True Then
  sum += large
 End If

 If CheckBox2.Checked = True Then
  sum += medium
 End If

 If CheckBox3.Checked = True Then
  sum += small
 End If
  Label5.Text = sum.ToString(“c”)

End Sub

Example 20.3

In this example, the text on the label can be formatting using the three check boxes that represent bold, italic and underline.

The Code

Public Class Form1

Private Sub ChkBold_CheckedChanged(sender As Object, e As EventArgs) Handles ChkBold.CheckedChanged
 If ChkBold.Checked Then
  LblDisplay.Font = New Font(LblDisplay.Font, LblDisplay.Font.Style Or FontStyle.Bold)
 Else
  LblDisplay.Font = New Font(LblDisplay.Font, LblDisplay.Font.Style And Not FontStyle.Bold)

 End If
End Sub

Private Sub ChkItalic_CheckedChanged(sender As Object, e As EventArgs) Handles ChkItalic.CheckedChanged
 If ChkItalic.Checked Then
  LblDisplay.Font = New Font(LblDisplay.Font, LblDisplay.Font.Style Or FontStyle.Italic)
 Else
  LblDisplay.Font = New Font(LblDisplay.Font, LblDisplay.Font.Style And Not FontStyle.Italic)
 End If
End Sub

Private Sub ChkUnder_CheckedChanged(sender As Object, e As EventArgs) Handles ChkUnder.CheckedChanged
 If ChkUnder.Checked Then
  LblDisplay.Font = New Font(LblDisplay.Font, LblDisplay.Font.Style Or FontStyle.Underline)
 Else
  LblDisplay.Font = New Font(LblDisplay.Font, LblDisplay.Font.Style And Not FontStyle.Underline)
 End If
End Sub
End Class

* The above program uses the CheckedChanged event to respond to the user selection by checking a particular checkbox, it is similar to the click event. The statement

LblDisplay.Font = New Font(LblDisplay.Font, LblDisplay.Font.Style Or FontStyle.Italic)

will retain the original font type but change it to italic font style.

LblDisplay.Font = New Font(LblDisplay.Font, LblDisplay.Font.Style And Not FontStyle.Italic)

will also retain the original font type but change it to regular font style. (The other statements employ the same logic)

The Output