Handle keyboard notification

KeyboardNotification.m

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillChangeFrame:) name:UIKeyboardWillChangeFrameNotification object:nil];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

#pragma mark - Notification
- (void)keyboardWillChangeFrame:(NSNotification *)sender
{
    NSDictionary *info = [sender userInfo];
    NSTimeInterval duration = [info[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    
    // Convert the keyboard frame from screen to view coorinates.
    CGRect keyboardScreenBeginFrame = [info[UIKeyboardFrameBeginUserInfoKey] CGRectValue];
    CGRect keyboardScrrenEndFrame = [info[UIKeyboardFrameEndUserInfoKey] CGRectValue];
    
    CGRect keyboardViewBeginFrame = [self.view convertRect:keyboardScreenBeginFrame fromView:self.view.window];
    CGRect keyboardViewEndFrame = [self.view convertRect:keyboardScrrenEndFrame fromView:self.view.window];
    CGFloat originDelta = keyboardViewEndFrame.origin.y - keyboardViewBeginFrame.origin.y;
    
    [UIView animateWithDuration:duration
                     animations:^{
                     
                     } completion:nil];
}