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Note Visual Basic has a special MaskedTextbox control. This control is an extended version of the normal Textbox and uses a nask to regulate what can be typed. The default VB.Net settings do not show the MaskedTextBox in the Toolbox. On my vesion of dotNet, the following steps added teh control to my toolbox, you may have to browse the internet for advice relating to other versions.

• Right Mouse Click on any item already in the toolbox
• Left Mouse Click on Show All

 
Note This page only uses normal textboxes/buttons. The commennts about maskestextbox are only intended to indicate that their may be an alternative solution to your coding problem.

 

• Add a normal TextBox to the form
• Make sure your textbox is called TextBox1
• Add the following code to your Form

Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
If e.KeyChar = Chr(8) Then Exit Sub ' 1
If Not "0123456789".Contains(e.KeyChar) Then
e.Handled = True ' 2
End If
End Sub
Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
Dim oldText As String = TextBox1.Text
Dim regex As New System.Text.RegularExpressions.Regex("[^0-9]")
Dim newText As String = regex.Replace(oldText, "") ' 3
If oldText <> newtext Then ' 4
TextBox1.Text = newText
End If
End Sub
Private Function Read_TextBox1() As Integer
Dim ret As Integer
If Not Integer.TryParse(TextBox1.Text, ret) Then Return 0 ' 5
Return ret
End Function


• 1 - Chr(8) is used by the delete key.
• 2 - Set a flag to ignore any keypress which is not a digit
• 3 - User could use copy/paste to force non-numeric data into textbox. There is no "onPaste" event. We must seach for invalid date whenver textChanged
• 4 - Changing textbox text manually after every keypress would be problematic. (Cursor position would change and control could be vulnearble to looping.) We can avoid this by only resetting textbox contents when we have removed invalid characters. This should only happen during an onPaste secenario.
• 5 - Thie function converts the String contained in TextBox1.text into an Integer. The integer test is required because the contol could contain a number to large for the integer data type.

 

• Add a normal TextBox to the form
• Make sure your textbox is called TextBox1
• Add the following code to your Form

Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
If e.KeyChar = Chr(8) Then Exit Sub
If Not "0123456789.".Contains(e.KeyChar) Then
e.Handled = True
End If
If e.KeyChar = "."c AndAlso TextBox1.Text.Contains("."c) Then
e.Handled = True
End If
End Sub
Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
Dim oldText As String = TextBox1.Text
Dim regex As New System.Text.RegularExpressions.Regex("[^0-9.]")
' this version does not alloiw exponential numbers
Dim newText As String = regex.Replace(oldText, "")
' ensure maximum of one decimal point
Dim parts() As String = newText.Split("."c)
If parts.Length > 2 Then
newText = parts(0) & "."c & parts(1)
End If
If oldText <> newText Then
TextBox1.Text = newText
MsgBox("changed")
End If
End Sub
Private Function Read_TextBox1() As Double
Dim ret As Double
If Not Double.TryParse(TextBox1.Text, ret) Then Return 0
Return ret
End Function

 
The user needs to be able to enter - or + to indicate whether number is negative or positive. However, we do not want - or plus appearing in teh middle of a number - that would be confusing. One silution is to move the - or + outside of the Textbox. If we place it in a button., next to the textbox, user can rapidly switch - or + by clicking the button.

• Add a normal TextBox to the form
• Make sure your textbox is called TextBox1
• Add a button to the left of the text box
• Make sure the button is called Button1
• Change the Button text to "+"
• Add the following code to your Form

Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
If e.KeyChar = Chr(8) Then Exit Sub
If Not "0123456789+-".Contains(e.KeyChar) Then
e.Handled = True
End If
If e.KeyChar = "+"c Then
Button1.Text = "+"
e.Handled = True
End If
If e.KeyChar = "-"c Then
Button1.Text = "-"
e.Handled = True
End If
End Sub Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
Dim oldText As String = TextBox1.Text
Dim regex As New System.Text.RegularExpressions.Regex("[^0-9+-]")
' this version does not allow exponential numbers
Dim newText As String = regex.Replace(oldText, String.Empty)
For Each c As Char In newText
If c = "+"c Then Button1.Text = "+"
If c = "-"c Then Button1.Text = "-"
Next
newText = newText.Replace("+"c, String.Empty).Replace("-"c, String.Empty)
If oldText <> newText Then
TextBox1.Text = newText
MsgBox("changed")
End If
End Sub
Private Function Read_TextBox1() As Integer
Dim ret As Integer
Dim num As String = TextBox1.Text.Replace("+"c, String.Empty)
num = num.Replace("-", String.Empty)
If Button1.Text = "-" Then num = "-" & num
If Not Integer.TryParse(num, ret) Then Return 0
Return ret
End Function

 
The user needs to be able to enter - or + to indicate whether number is negative or positive. However, we do not want - or plus appearing in teh middle of a number - that would be confusing. One silution is to move the - or + outside of the Textbox. If we place it in a button., next to the textbox, user can rapidly switch - or + by clicking the button.

• Add a normal TextBox to the form
• Make sure your textbox is called TextBox1
• Add a button to the left of the text box
• Make sure the button is called Button1
• Change the Button text to "+"
• Add the following code to your Form

Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
If e.KeyChar = Chr(8) Then Exit Sub
If Not "0123456789+-.".Contains(e.KeyChar) Then
e.Handled = True
End If
If e.KeyChar = "."c AndAlso TextBox1.Text.Contains("."c) Then
e.Handled = True
End If
If e.KeyChar = "+"c Then
Button1.Text = "+"
e.Handled = True
End If
If e.KeyChar = "-"c Then
Button1.Text = "-"
e.Handled = True
End If
End Sub
Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
Dim oldText As String = TextBox1.Text
Dim regex As New System.Text.RegularExpressions.Regex("[^0-9+.-]")
' this version does not allow exponential numbers
Dim newText As String = regex.Replace(oldText, String.Empty)
For Each c As Char In newText
If c = "+"c Then Button1.Text = "+"
If c = "-"c Then Button1.Text = "-"
Next
newText = newText.Replace("+"c, String.Empty).Replace("-"c, String.Empty)
Dim parts() As String = newText.Split("."c)
If parts.Length > 2 Then
newText = parts(0) & "." & parts(1)
End If
If oldText <> newText Then
TextBox1.Text = newText
MsgBox("changed")
End If
End Sub
Private Function Read_TextBox1() As Integer
Dim ret As Integer
Dim num As String = TextBox1.Text.Replace("+"c, String.Empty)
num = num.Replace("-", String.Empty)
If Button1.Text = "-" Then num = "-" & num
If Not Integer.TryParse(num, ret) Then Return 0
Return ret
End Function

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