WPF - MVVM Textbox restrict to specific characters

Question

I am trying to make text box accept only specific characters.

My TextBox is bound to the following:

    private string _CompanyID;
    public string          


        

Answer 1

You should use a custom UI element there that restricts the input on the view-side using “classic” solutions like change listeners.

For example, you can just create a simple subtype of TextBox that overrides the OnPreviewTextInput method. There, you can decide when some input should go through, or when you want to prevent it.

For example, this is a custom TextBox that takes only characters from the ASCII alphabet:

public class AlphabetTextBox : TextBox
{
    private static readonly Regex regex = new Regex("^[a-zA-Z]+$");

    protected override void OnPreviewTextInput(TextCompositionEventArgs e)
    {
        if (!regex.IsMatch(e.Text))
            e.Handled = true;
        base.OnPreviewTextInput(e);
    }
}

Of course, you could also make the regular expression a property of the text box and allow people to set it from XAML. That way, you would get a very reusable component which you can use for various applications.