How to allow only numbers in textbox?

[mcerk]

Hi. I'm triing to do my own textbox that would allow only numeric characters to be displayed (and it will allso allow . and ,).

 

So. I can prevent this characters to be pressed? how can I do it?

I wrote some code, but I don't think it will go this way.

 

thank you a lot

 

Private Sub myTextBox_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles MyBase.KeyDown
       'if not pressed a key between 0 and 9 or , or .
       If Not (e.KeyValue >= 96 And e.KeyValue <= 105) Or e.KeyValue = 190 Or e.KeyValue = 188 Then
           'how can I erase pressed key? or is there better way of doing it?
       End If
End Sub

[philiplcp]

Hi. I'm triing to do my own textbox that would allow only numeric characters to be displayed (and it will allso allow . and ,).

 

So. I can prevent this characters to be pressed? how can I do it?

I wrote some code, but I don't think it will go this way.

 

thank you a lot

 

Private Sub myTextBox_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles MyBase.KeyDown
       'if not pressed a key between 0 and 9 or , or .
       If Not (e.KeyValue >= 96 And e.KeyValue <= 105) Or e.KeyValue = 190 Or e.KeyValue = 188 Then
           'how can I erase pressed key? or is there better way of doing it?
       End If
End Sub

 

hope the following can help you :D

 

Private Sub myTextBox_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles myTextBox.KeyDown
       If System.Text.RegularExpressions.Regex.IsMatch(CStr(e.KeyValue), "^[+-]?(\d*\.?\d+|\d+\.?\d*)([eE][+-]?\d+)?$") Then
           ........
       Else
           MsgBox("please enter digit")
       End If
   End Sub

Edited January 16, 2005 by philiplcp

[mcerk]

I tried this, but this thing somehow doesn't work. The problem is, that when KeyDown event is triggered, the key (char) is allready displayed in textbox

[philiplcp]

I tried this' date=' but this thing somehow doesn't work. The problem is, that when KeyDown event is triggered, the key (char) is allready displayed in textbox[/quote']

 

try the following

 

    Private Sub myTextBox_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles myTextBox.KeyDown
       If System.Text.RegularExpressions.Regex.IsMatch(CStr(e.KeyValue), "^[+-]?(\d*\.?\d+|\d+\.?\d*)([eE][+-]?\d+)?$") Then
           ........
       Else
           dim txt as string = myTextBox.text
           myTextBox.text=txt.substring(0,txt.length-1)
       End If
   End Sub

[PlausiblyDamp]

Set e.Handled = true within the event handler and it should prevent the key stroke appearing in the textbox

[mutant]

KeyPress event is the one you are looking for. And there is a much easier way to do that than RegEx I think :).

 

   Private Sub Text_KeyPress(args...)
   If Not Char.IsDigit(e.KeyChar) And Not Char.IsPunctuation(e.KeyChar)
        e.Handled = True 'tell the textbox not include the character
        MessageBox.Show("numbers and punctuation only please!")
   End If
   End Sub

Now, punctuation includes other signs too rather than only "." and "," so its up to you if you want to check like that or compare it otherwise.

[mcerk]

KeyPress event is the one you are looking for. And there is a much easier way to do that than RegEx I think :).

 

   Private Sub Text_KeyPress(args...)
   If Not Char.IsDigit(e.KeyChar) And Not Char.IsPunctuation(e.KeyChar)
        e.Handled = True 'tell the textbox not include the character
        MessageBox.Show("numbers and punctuation only please!")
   End If
   End Sub

Now, punctuation includes other signs too rather than only "." and "," so its up to you if you want to check like that or compare it otherwise.

 

 

tx, this works perfectly

[Jaco]

KeyPress has one very critical flaw that is almost always overlooked by junior programmers:

 

Are you going to disable pasting into the textbox? If not, then KeyPress won't work - you need to examine the textbox contents after every TextChanged event.

[mcerk]

I See. but in TextChanged event I can not use:

 

e.Handled = True

 

So I solved pasting problem with some other procedure...

 

 

Do you have more elegant solution?

[dynamic_sysop]

you can set the TextBox's style to accept only numbers being typed , but then you have to handle the pasting of text ( WM_PASTE ) , here's a quick example i knocked up for you ...

   Private Const ES_NUMBER As Int32 = &H2000I
   Private Const GWL_STYLE As Int32 = -16
   Private Declare Function GetWindowLong Lib "user32.dll" Alias "GetWindowLongA" (ByVal hwnd As IntPtr, ByVal nIndex As Int32) As Int32
   Private Declare Function SetWindowLong Lib "user32.dll" Alias "SetWindowLongA" (ByVal hwnd As IntPtr, ByVal nIndex As Int32, ByVal dwNewLong As Int32) As Int32

   Private numertext As NumericTextbox '/// this will handle WM_PASTE

   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
       Dim style As Int32 = GetWindowLong(TextBox1.Handle, GWL_STYLE)
       style += ES_NUMBER
       SetWindowLong(TextBox1.Handle, GWL_STYLE, style)
       '/// now i subclass the textbox to handle the paste message / CTL + V
       numertext = New NumericTextbox(TextBox1.Handle)
   End Sub

Public Class NumericTextbox
   Inherits NativeWindow

   Private Const WM_PASTE As Int32 = &H302

   Public Sub New(ByVal handle As IntPtr)
       MyBase.AssignHandle(handle)
   End Sub

   Protected Overrides Sub WndProc(ByRef m As Message)
       If Not m.Msg = WM_PASTE Then
           MyBase.WndProc(m)
       ElseIf m.Msg = WM_PASTE Then
           '/// lets get the clipboard info that's being pasted
           If Clipboard.GetDataObject.GetDataPresent(DataFormats.Text) Then
               Dim s As String = DirectCast(Clipboard.GetDataObject.GetData(DataFormats.Text), String)
               If IsNumeric(s) Then '/// it's a numeric string being pasted
                   MyBase.WndProc(m)
               End If
           End If
       End If
   End Sub
End Class

hope it helps :)