主题：怎样写代码使textbox,只可以唯一写5个字符才合法

Validating事件

If e.sender.text > "" Then
    If e.sender.text.length <> 5 Then
        msgbox("不是5位")
        e.cancel = True
    Else
        For i As Integer = 0 To e.Sender.text.length-1
            For j As Integer = i+1 To e.sender.text.length-1
                If e.sender.Text(i) = e.sender.Text(j) Then
                    msgbox(i & "位 和 " & j & "位重复")
                    e.cancel = True
                    Return
                End If
            Next
        Next
    End If
End If