UITextField and Keyboard Notifications - strange order

So I've set up a notification for the keyboard appearance event. Now let us consider a UITextView and a UITextField.

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(keyboardWillShow:)
                                             name:UIKeyboardWillShowNotification
                                           object:nil];

The selector is:

- (void)keyboardWillShow:(NSNotification *)notification {

        keyboardSize = [[[notification userInfo] objectForKey:UIKeyboardFrameBeginUserInfoKey] CGRectValue].size;
}

In case of a UITextView, the delegate method - (void)textViewDidBeginEditing:(UITextView *)textView is fired AFTER the keyboardWillShow: method. So keyboardSize has the keyboard's actual size and I'm able to use that inside the textview delegate method.

However in case of a UITextField, the corresponding delegate method - (void)textFieldDidBeginEditing:(UITextField *)textField is fired BEFORE the keyboardWillShow: method.

Why is this so? How do I get the keyboard's CGSize in the textfield's case as now it just returns zero because the textfield delegate is called first and not the keyboard selector.