How can I allow only 0 or 1 to be entered in a TextBox?

Question

How can I limit the TextBox control to only allow the values 0 and 1?

Thanks. And I have one more question: How can I disable put text from clipboard in my textbox c

Answer 1

If you do want to show the numbers rather than a check or something but only want to allow 0 or 1 you could use a NumericUpDown control and set min to 0 max to 1 and step to 1.

If you do actually need a textbox I'd use Filip's answer but I'd set the MaxLength of it to 1 to avoid having to worry about 00, 11 or 01 or similar values.

Answer 2

By using the event KeyPress

private void NumericOnlyKeyBox_KeyPress(object sender, KeyPressEventArgs e)
{
    var validKeys = new[] { Keys.Back, Keys.D0, Keys.D1 };

    e.Handled = !validKeys.Contains((Keys)e.KeyChar);
}

Setting e.Handled to true / false indicates if the character should be accepted to the box or not.

You can read more about KeyPressEventArgs on MSDN.

Note

Keys.Delete should cover Keys.Delete, Keys.Backspace and other "Back" buttons.

Answer 3

You may want to see the answer to this related question:

C# Input validation for a Textbox: float