iOS Masonry 布局（三） - UIScrollView

UIScrollView使用Masonry布局最大的难点在于如何让子视图追随ScrollView滑动。
目前使用最广泛的解决方式是为滑动视图添加一个过渡视图，之后将所有的子视图添加到过渡视图上，然后分别设置过渡视图与滑动视图约束（注：竖向滑动时，需将过渡视图的宽度固定；横向滑动时，需将过渡视图的高度固定）、过渡视图与第一个子视图边缘约束、过渡视图与最后一个子视图边缘约束。

本示例以垂直滑动为例：

    UIScrollView *scrollView = [[UIScrollView alloc] init];
    scrollView.showsVerticalScrollIndicator = NO;
    scrollView.showsHorizontalScrollIndicator = NO;
    scrollView.backgroundColor = [UIColor redColor];
    
    UIView *containerView = [[UIView alloc] init];
    containerView.backgroundColor = [UIColor yellowColor];
    
    [self.view addSubview:scrollView];
    [scrollView addSubview:containerView];
    
    [scrollView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.edges.equalTo(self.view);
    }];
    [containerView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.edges.equalTo(scrollView);
        make.width.equalTo(scrollView.mas_width);
    }];
    
    UIView *lastView;
    NSInteger viewsNumber = 20;
    
    for (int i = 0; i<viewsNumber; i++) {
        UIView *view= [[UIView alloc] init];
        view.backgroundColor = [UIColor colorWithRed:(arc4random()%255)/255.0 green:(arc4random()%255)/255.0 blue:(arc4random()%255)/255.0 alpha:1.f];
        [containerView addSubview:view];
        [view mas_makeConstraints:^(MASConstraintMaker *make) {
            if (0 == i) {
                //第一个视图
                make.top.equalTo(containerView.mas_top);
            }else {
                make.top.equalTo(lastView.mas_bottom);
            }
            make.left.equalTo(containerView.mas_left);
            make.right.equalTo(containerView.mas_right);
            make.height.mas_equalTo(66.f);
            if (viewsNumber == i+1) {
                //最后一个视图
                make.bottom.equalTo(containerView.mas_bottom);
            }
            
        }];
        lastView = view;
    }

效果图：