Question

I need to be able to lock down the valid characters in a textbox, I presently have a regex which I can check each character against such as

[A-Za-z]

would lock down to just Alpha characters.

protected override void OnKeyPress(KeyPressEventArgs e) {   if (e.KeyChar == (char)Keys.Back)   {     base.OnKeyPress(e);     return;   }   if (String.IsNullOrEmpty(this._ValidCharExpression))   {     base.OnKeyPress(e);   }   else   {     bool isValidChar = Regex.Match(e.KeyChar.ToString(),this._ValidCharExpression).Success;     if (isValidChar)     {       base.OnKeyPress(e);     }     else     {       e.Handled = true;     }   } } 

I had placed the regex code in the OnKeyPress code, but I wat to allow all special keys, such as Ctrl-V, Ctrl-C and Backspace to be allowed.

As you can see I have the backspace key being handled. However, Ctrl-V, for example cannot see the V key because it runs once for the ctrl key but does not see any modifiers keys.

What is the best way to handle this situation?

Answer 1

You can use one of the OnKeyPress / OnKeyUp / OkKeyDown events and then use the Char.IsLetter method to check that the entered key is a letter.