Using Keypress event with Regex

Question

I’m making an application C# in Windows Form using .Net Framework 3.5. In this application I have a textbox for the input of CPF or CNPJ.

I need this field to have only CPF/CNPJ numbers and characters (./-). I would like to validate this field in the event Keypress using Regex. Would it be possible?

Answer 1

Instead of validating the textbox in the KeyPress, do in the Validating. This avoids the use of Regex with each button pressed.

private void textBox_Validating(object sender, CancelEventArgs e)
{
    // Corra o regex aqui. Caso não seja o que pertende, cancele o evento.
    e.Cancel = true; // Cancela o evento e impede o utilizador de sair da textbox
}

When cancelling the event, the user is prevented from taking the focus of the textbox and can bring up a tooltip or change the color of textbox to indicate that there is an error with the value entered.