textbox에서 숫자만 입력

 Private Sub txtagent(sender As System.Object, e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress, TextBox3.KeyPress, TextBox2.KeyPress
        If Not (Char.IsDigit(e.KeyChar) OrElse e.KeyChar = Convert.ToChar(Keys.Back)) Then
            e.Handled = True
        End If
    End Sub