IPhone Objective-C only enable a button if NSTextfield is not blank

I have a button that I only want enabled when a textfield is not blank. I have been trying to do this by implementing the following method, without any luck.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{

Is there another delegate method that I could implement that gets fired after the text is changed? In this method is there some way to tell what ke开发者_如何学Goy is being pressed, if it's a delete or something like that?

You can just check for string.length == 0 and range.length > 0;. This denotes a deletion. However, what you really want is to just do the pending modification and then check that you still have a non-empty string.

Something like this (typed in, not compiled):

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    NSString *testString = [textField.text stringByReplacingCharactersInRange:range withString:string];

    if( testString.length )
        myButton.enabled = YES;
    else
        myButton.enabled = NO;

    return YES;
}