create a keypress event like windowform

hi all

i port my window form inherits textbox to asp.net
this textbox only allow numeric to be enter during keypress event.
but it is not working on asp.net. how do i write a keypress event on asp.net?
Public Class NumbericText : Inherits TextBox Public Event OnEnterKeyPress() Dim MyInput As Cinput Public Property CharacterInput() As Cinput Get Return Me.MyInput End Get Set(ByVal value As Cinput) Me.MyInput = value End Set End Property Protected Sub OnKeyPress(sender As Object, e As EventArgs) MyBase.OnTextChanged(e) If Asc(MyBase.Text) = 13 Then RaiseEvent OnEnterKeyPress() End If Select Case Me.MyInput Case Cinput.CharactersOnly If IsNumeric(MyBase.Text) Then MyBase.Text = MyBase.Text End If ...