Disable string characters in textbox

Private Sub Textbox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles Textbox1.KeyPress
        If e.KeyChar = "."c Then
            e.Handled = (CType(sender, TextBox).Text.IndexOf("."c) <> -1)
        ElseIf e.KeyChar <> ControlChars.Back Then
            e.Handled = ("0123456789".IndexOf(e.KeyChar) = -1)
        End If
    End Sub