iOS 键盘处理

键盘遮挡问题：

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 监听键盘通知
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

- (void)keyboardWillShow:(NSNotification *)note {
    // 取出键盘最终的frame
    CGRect rect = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
    // 取出键盘弹出需要花费的时间
    double duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    // 修改约束
    self.bottomSpacing.constant = rect.size.height;
    [UIView animateWithDuration:duration animations:^{
        [self.view layoutIfNeeded];
    }];
}

- (void)keyboardWillHide:(NSNotification *)note {
    // 取出键盘弹出需要花费的时间
    double duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    // 修改约束
    self.bottomSpacing.constant = 0;
    [UIView animateWithDuration:duration animations:^{
        [self.view layoutIfNeeded];
    }];
}