Enabling done button after inserting one char in a textfield: textFieldDidEndEditing: or textFieldShouldBeginEditing: or?

Question

I would like to enable the done button on the navbar (in a modal view) when the user writes at least a char in a uitextfield. I tried:

• textFieldDidEndEditing:

Answer 1

try and go with:

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
int lenght = editingTextField.text.length - range.length + string.length;
if (lenght > 0) {
    yourButton.enabled = YES;
} else { 
    yourButton.enabled = NO;
}
return YES;

}

This answer was marked correct when infact a better solution existed by 'w4nderlust' below. This answer is theirs, let them take the credit!