iOS - detect when user copy to clipboard - [UIPasteboard generalPasteboard]

Question

quick easy question

while using a WebView with some text in it - the user can select a snippet of text from it and press a UIButton which I created - running the following action:

-(IBAction)copyToClip
{
    NSString *copyClip = [UIPasteboard generalPasteboard].string;
    NSLog(@"Clip = %@",copyClip);
    // (works fine)
}

I would like to call the same function without a UIButton, thus when the user did a "copy" action it will activate the above code. (I assume a listener)

what would be the appropriate listener for this?