При вводе любых символов, кроме цифр, выдавать сообщение об ошибке

r1 = Convert.ToDouble(TextBox1.Text)

Public Class Form1
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        RadioButton1.Text = "Последовательно"
        RadioButton2.Text = "Параллельно"
    End Sub
 
    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        Dim r1 As Double
        Dim r2 As Double
        Dim Result As Double
        Dim style As MsgBoxStyle = MsgBoxStyle.Critical
 
        While (IsNumeric(TextBox1.Text) = False) Or (IsNumeric(TextBox2.Text) = False)
            MsgBox("R должено быть числом", style)
            Exit While
        End While
 
        r1 = Convert.ToDouble(TextBox1.Text)
        r2 = Convert.ToDouble(TextBox2.Text)
        If RadioButton1.Checked = True Then TextBox3.Text = Convert.ToString(r1 + r2)
 
    End Sub
End Class

    Private Sub TotalSumm_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress, TextBox2.KeyPress
        Try
            Dim txtBox As TextBox = DirectCast(sender, TextBox)
            Dim ch As Char = e.KeyChar
            If ch = "46" AndAlso txtBox.Text.IndexOf("."c) <> -1 Then
                e.Handled = True
                Return
            End If
            If e.KeyChar <> ControlChars.Back Then
                e.Handled = Not (Char.IsDigit(e.KeyChar) Or e.KeyChar = "/")
            End If
        Catch ex As Exception
        End Try
    End Sub