Prevent numbers from being pasted in textbox in .net windows forms

Question

I have prevented numbers from being typed in text box using key down event. But when using Ctrl+V or pasting content through mouse, the numbers are being entered in the text

Answer 1

use the TextBox.TextChanged event. Then use the same code as you have in the KeyDown event. In fact, you no longer need the keydown event

Answer 2

You can use the JavaScript change event (onchange) instead of the keydown event. It'll check only when the user leaves the textbox though.

Answer 3

On quite simple approach would be to check the text using the TextChanged event. If the text is valid, store a copy of it in a string variable. If it is not valid, show a message and then restore the text from the variable:

string _latestValidText = string.Empty;
private void TextBox_TextChanged(object sender, EventArgs e)
{
    TextBox target = sender as TextBox;
    if (ContainsNumber(target.Text))
    {
        // display alert and reset text
        MessageBox.Show("The text may not contain any numbers.");
        target.Text = _latestValidText;
    }
    else
    {
        _latestValidText = target.Text;
    }
}
private static bool ContainsNumber(string input)
{
    return Regex.IsMatch(input, @"\d+");
}

This will handle any occurrence of numbers in the text, regardless of where or how many times they may appear.