iOS 使用masonry 添加动画

预先定义一个约束的全局变量，用来接收需要变化的约束

@property (nonatomic, strong) MASConstraint *hudViewTop;

UIWindow *window = [UIApplication sharedApplication].keyWindow;

    [windowaddSubview:self.hudView];

    [self.hudView makeConstraints:^(MASConstraintMaker *make) {

        self.hudViewTop = make.top.equalTo(window.top).offset(-70);

        make.left.equalTo(window.left).offset(20);

        make.right.equalTo(window.right).offset(-20);

        make.height.equalTo(@70);

    }];

- (void)_showAndHideHud{//出现隐藏头部hud

    UIWindow *window = [UIApplication sharedApplication].keyWindow;

    [self.hudViewTop uninstall];//先销毁约束

    [UIView animateWithDuration:1.0 animations:^{//修改约束驾到动画的过程中

        [self.hudView updateConstraints:^(MASConstraintMaker *make) {

            self.hudViewTop = make.top.equalTo(window.top).offset(NAVBAR_HEIGHT/2);

        }];

        [window layoutIfNeeded];//一定要加，---父视图---  刷新

    }];

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{//gcd 延迟调用 

        [self.hudViewTop uninstall];

        [UIView animateWithDuration:1.0 animations:^{

            [self.hudView updateConstraints:^(MASConstraintMaker *make) {

                make.top.equalTo(window.top).offset(-70);

            }];

            [windowlayoutIfNeeded];

        }];

    });

}