Limiting Keypresses

Question

I am using C#, Visual Studio 2010, Windows Form Application, and working with a textbox.

For this textbox, I don't want the user to be able to press any key aside from numbers, backspace, and letters (lower and upper case). Any other characters (such as @#$%^) will result in a beep and reject the keypress.

What would be the code to check for those range of keys?

Thank you!

You know how to handle key events? You know how to compare characters? What have you tried so far? Have you done any research yet? — marsze, Jan 20 '14 at 13:29

score 1 · Accepted Answer · edited May 23 '17 at 12:28

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if (!(Char.IsLetter(e.KeyChar) || Char.IsDigit(e.KeyChar) || Char.IsControl (e.KeyChar))){
        e.Handled = true;
        Console.Beep(); 
    }
}

But, like MusiGenesis said in this question: Allow only alphanumeric in textbox

Handling the KeyDown or KeyPress events is not enough. A user can still copy-and-paste invalid text into the textbox.

A somewhat better way is to handle the TextChanged event, and strip out any offending characters there. This is a bit more complicated, as you have to keep track of the caret position and re-set it to the appropriate spot after changing the box's Text property.

Depending on your application's needs, I would just let the user type in whatever they want, and then flag the textbox (turn the text red or something) when the user tries to submit.

Limiting Keypresses

1 Answers1