change view based on keyboard height

ViewControllerBasedOnKeyboard.h

@property CGFloat currentKeyboardHeight;
@property (weak, nonatomic) IBOutlet NSLayoutConstraint *btnBottomConstraint;

ViewControllerBasedOnKeyboard.m

- (void)viewDidAppear:(BOOL)animated{

    [self addKeyboardObserver];
}
 
- (void)viewDidDisappear:(BOOL)animated{

    [self removeKeyboardObserver];
}

-(void) addKeyboardObserver{
  
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
}
 
-(void) removeKeyboardObserver{
  
    [[NSNotificationCenter defaultCenter] removeObserver:self
                                                    name:UIKeyboardWillHideNotification
                                                  object:nil];
    
    [[NSNotificationCenter defaultCenter] removeObserver:self
                                                    name:UIKeyboardWillShowNotification
                                                  object:nil];
}
 
- (void)keyboardWillShow:(NSNotification*)notification {
    
    NSLog(@"keyboardWillShow");
    
    NSDictionary *info = [notification userInfo];
    CGSize kbSize = [[info objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue].size;
    
    CGFloat bottomSpace = kbSize.height + SPACE_UNDER_BUTTON;
    if(self.btnBottomConstraint.constant == bottomSpace) return;
    
    [self.view layoutIfNeeded];
    [UIView animateWithDuration: 0.3 animations: ^{
        self.btnBottomConstraint.constant = bottomSpace;
        [self.view layoutIfNeeded];
    }];
    
    NSLog(@"view height:%f, width:%f", self.view.frame.size.height, self.view.frame.size.width);
}

- (void)keyboardWillHide:(NSNotification*)notification{
    
    NSLog(@"keyboardWillHide");
    
    if(self.btnBottomConstraint.constant == SPACE_UNDER_BUTTON) return;
    
    [self.view layoutIfNeeded];
    [UIView animateWithDuration: 0.3 animations: ^{
        self.btnBottomConstraint.constant = SPACE_UNDER_BUTTON;
        [self.view layoutIfNeeded];
    }];
    
    NSLog(@"view height:%f, width:%f", self.view.frame.size.height, self.view.frame.size.width);
}

view를 자르는 방식말고, NSLayoutConstraint를 변경하는 방식이 자연스러움