Question

I have a textbox and I am using the following to validate the user can only add numbers, but how can I let the user to write only one “.”

Private Sub txtDiagnostic_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtConsultor.KeyPress
        If e.KeyChar <> ChrW(Keys.Back) Then
            If Char.IsNumber(e.KeyChar) Then
            Else
                e.Handled = True
            End If
        End If
    End Sub

I was planing to use contains() or something but how can I realize the textbox has
only one dot? or how to allow the user can write a single dot and only one?

Answer 1

add this line before your first IF

If (e.KeyChar.ToString = ".") And (txtDiagnostic.Text.Contains(e.KeyChar.ToString)) Then
     e.Handled = True
     Exit Sub
End If