Restrict numbers and letters in textbox - C#

Question

I want to restrict what numbers and letters can be entered into a textbox. Let\'s say I only want to allow numbers 0-5 and letters a-d (both lower and uppercase). I already tri

Answer 1

Override the PreviewKeyDownEvent like this:

    private void textBox1_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
    {
        if (e.KeyCode == Keys.A || e.KeyCode == Keys.B || ...)
            e.IsInputKey = true;
        else
            e.IsInputKey = false;
    }

This will tell the textBox which keys it will consider as a user input or not.