How to validate a blank maskedtextbox?

Question

In case the maskedtextboxTEL [phone] would return a error provider and would not proceed until it has been completed.

Answer 1

You can use the método String.Isnullorwhitespace.

Code

 if (String.IsNullOrWhiteSpace(txt_Telefone.Text))
 {
    errorProvider1.SetError(txt_Telefone, "Preencha o telefone ! ");
 }