// UIView如果使用AutoLayout 必須寫此方法

+ (BOOL)requiresConstraintBasedLayout
{
    return YES;
}

//按鈕的動(dòng)態(tài)效果修改時(shí) 此方法為 系統(tǒng)自帶方法

// this is Apple's recommended place for adding/updating constraints
- (void)updateConstraints {

    [self.growingButton updateConstraints:^(MASConstraintMaker *make) {
        make.center.equalTo(self);
        make.width.equalTo(@(self.buttonSize.width)).priorityLow();
        make.height.equalTo(@(self.buttonSize.height)).priorityLow();
        make.width.lessThanOrEqualTo(self); //按鈕的最大寬度 <= 當(dāng)前self的寬度
        make.height.lessThanOrEqualTo(self); //按鈕的最大高度 <= 當(dāng)前self的寬度
    }];
    
    //according to apple super should be called at end of method
    [super updateConstraints]; //蘋果規(guī)定最后調(diào)用這個(gè)
}

//按鈕觸發(fā)的時(shí)候

1.   [self setNeedsUpdateConstraints]; //必須調(diào)用
2.   [self updateConstraintsIfNeeded]; //更新約束
3.   [UIView animateWithDuration:0.4 animations:^{
        [self layoutIfNeeded];
      }];   //動(dòng)畫效果

//代碼演示

- (void)didTapGrowButton:(UIButton *)button {
    if (!self.zoom) {
        self.buttonSize = CGSizeMake(self.buttonSize.width * 5, self.buttonSize.height * 6);
        self.zoom = YES;
    } else {
        self.buttonSize = CGSizeMake(self.buttonSize.width / 5, self.buttonSize.height /  6);
        self.zoom = NO;
    }

    // tell constraints they need updating
    [self setNeedsUpdateConstraints];

    // update constraints now so we can animate the change
    [self updateConstraintsIfNeeded];

    [UIView animateWithDuration:0.4 animations:^{
        [self layoutIfNeeded];
    }];
}