TextBox not editing after SelectAll in vb.net

Question

I have an issue, The thing is I have to allow user to enter numeric value in text box up to one decimal point,

When all text selected and I try try to edit text by entering any numeric key, It wont let it change.

Here is the text box with value.

The code behind, Keypress

Private Sub TextBox1_KeyPress(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
    If Regex.IsMatch(TextBox1.Text, "\.\d") Then
        e.Handled = True
    End If
End Sub

Kindly anybody help or suggest better way.

I have added this code but I am unable to restrict user not to enter more then one decimal point value.

 If Not ((Asc(e.KeyChar) >= 48 And Asc(e.KeyChar) <= 57) Or Asc(e.KeyChar) = 46 Or Asc(e.KeyChar) = 8 Or Asc(e.KeyChar) = 127) Then
        e.KeyChar = ""
        e.Handled = False
    End If

Answer 1

Try this: (not regex tho), but works great for numerics.

It allows for 1 x negative symbol, one fullstop (point), using backspace, and any numerics..

       Private Sub priceTextBox_KeyPress(sender As Object, e As KeyPressEventArgs) Handles priceTextBox.KeyPress
       If IsNumeric(e.KeyChar.ToString) = False Then

            If e.KeyChar.ToString = "." And priceTextBox.Text.Contains(".") Then e.Handled = True
            If e.KeyChar.ToString = "-" And priceTextBox.Text.Contains("-") Then e.Handled = True

            If e.KeyChar.ToString <> "." Then
                If e.KeyChar <> ControlChars.Back Then
                    If e.KeyChar <> "-" Then
                        e.Handled = True
                    End If
                End If
            End If
        End If
        End Sub

EDIT

This allows for the above numerics, as well as only 1 decimal point. I kept it simple with more code lines to show steps, so you can see what actually happens. I am sure it can be improved, this is a quick and dirty version...

• Allows for Globalization of the decimal character

• Also catches a "paste" into the textbox, that normally circumvents the keypress catch routines

  Dim lastProperText As String = ""
  
  Private Sub priceTextBox_TextChanged(sender As Object, e As EventArgs) Handles priceTextBox.TextChanged
  
    If priceTextBox.Text = "" Then Exit Sub
    If IsNumeric(priceTextBox.Text) = False Then priceTextBox.Text = lastProperText
    If _containsDecimal(priceTextBox.Text, 2) = True Then priceTextBox.Text = lastProperText
  
  End Sub
  
  Private Sub priceTextBox_KeyPress(sender As Object, e As KeyPressEventArgs) Handles priceTextBox.KeyPress
      Dim decimalSeparator As String = Globalization.CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator
  
      If IsNumeric(e.KeyChar.ToString) = False Then
  
          If e.KeyChar.ToString = decimalSeparator And priceTextBox.Text.Contains(decimalSeparator) Then e.Handled = True
          If e.KeyChar.ToString = "-" And priceTextBox.Text.Contains("-") Then e.Handled = True
  
          'allow backspace here
          If e.KeyChar = ControlChars.Back Then Exit Sub
  
          If e.KeyChar.ToString <> decimalSeparator Then
              If e.KeyChar <> ControlChars.Back Then
                  If e.KeyChar <> "-" Then
  
                      e.Handled = True
  
                  End If
              End If
          End If
      End If
  
      'BUG FIX
      If priceTextBox.SelectionStart > priceTextBox.Text.Length - 2 Then
        If _containsDecimal(priceTextBox.Text, 1) = True Then e.Handled = True
      End If
      '/BUG FIX
  
      'keep last good format.. we will use this in case something gets apsted in that does not meet our format...
      lastProperText = priceTextBox.Text
  
  End Sub
  
  Private Function _containsDecimal(stringtoCheck As String, decimalNumber As Integer) As Boolean
  
      Dim decimalSeparator As String = Globalization.CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator
  
      'check to allow only 1 decimal point
      Dim positionOfPoint As Integer = 0
  
      'get position of decimal point (.)
      positionOfPoint = InStr(stringtoCheck, decimalSeparator)
  
      'check if there are not characters after decimal point... 
      'if nothin after decimal point, allow this keypress, 
      'if there is already something after decimal point, escape this keypress
  
      'get length of string after "."
      Dim stringTail As String = ""
  
      If Not positionOfPoint = 0 Then
          stringTail = Mid(stringtoCheck, positionOfPoint)
          If stringTail.Length > decimalNumber Then
              Return True
          End If
      End If
  
  End Function