Public Function Sadece_Sayisal(ByVal e As System.Object)
        Try
            If Not IsNumeric(e.Text) And e.Text <> "" Then
                MsgBox("Lütfen sayısal değer giriniz !!!!", vbCritical)
                e.Text = ""
                e.Focus()
            End If
            Return e
        Catch ex As Exception
            MsgBox(ex.Message)
            Return Nothing
        End Try
    End Function

 Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
        Sadece_Sayisal(TextBox1)
 End Sub