怎么实现不让选中指定的字符

如何实现不让选中指定的字符.
例如,一个文本框中 有 "1232BD"几个字符,只能选种数字,而不能选中字母.如何写?

[解决办法]
用富文本框，在selchange事件里处理
[解决办法]

VB code

Option Explicit 
  
 Dim flag As Boolean 
  
  
 Private Sub Form_Load() 
   flag = False 
 End Sub 
  
 Private Sub Text1_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) 
   flag = True 
 End Sub 
  
 Private Sub Text1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single) 
  
   If flag = True And Text1.SelLength > 0 Then 
     Dim start As Long 
     Dim length As Long 
     Dim text As String 
     Dim i As Long 
     start = Text1.SelStart 
     length = Text1.SelLength 
     text = Text1.SelText 
     For i = 1 To length 
       Dim c As Integer 
       c = AscW(Mid$(text, i, 1)) 
       If Not (c > 48 And c  <= 57) Then 
         Text1.SelLength = 0 
        
       End If 
      
     Next 
      
      
   End If 
 End Sub 
  
 Private Sub Text1_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single) 
   flag = False 
 End Sub