首先，添加和移除通知

- (void)viewDidAppear:(BOOL)animated{
    [super viewDidAppear:animated];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWillShow:)
                                                 name:UIKeyboardWillShowNotification
                                               object:nil];
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWillHide:)
                                                 name:UIKeyboardWillHideNotification
                                               object:nil];
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    [[NSNotificationCenter defaultCenter] removeObserver:self
                                                    name:UIKeyboardWillShowNotification
                                                  object:nil];
    
    [[NSNotificationCenter defaultCenter] removeObserver:self
                                                    name:UIKeyboardWillHideNotification
                                                  object:nil];
}

之后，响应通知

- (void)keyboardWillShow:(NSNotification *)notification {
    
    NSDictionary *userInfo = [notification userInfo];
    NSValue *aValue = [userInfo objectForKey:UIKeyboardFrameEndUserInfoKey];
    
    CGRect keyboardRect = [aValue CGRectValue];
    keyboardRect = [self.view convertRect:keyboardRect fromView:nil];
    
    keyboardHeight = keyboardRect.size.height;
    
    CGRect frame = self.view.bounds;
    frame.size.height -= keyboardHeight;
    self.contentScrollView.frame = frame;
    self.contentScrollView.contentSize = CGSizeMake(SCREEN_WIDTH, CGRectGetMaxY(self.confirmBtn.frame)+ 20);
}

- (void)keyboardWillHide:(NSNotification *)notification {
    
    keyboardHeight = 0;
    
    self.contentScrollView.frame = self.view.bounds;
//    self.contentScrollView.contentSize = self.view.bounds.size;
}