UIScrollView 遇到了AutoLayout之后其contentSize 的计算

UIScrollView 的特殊之处就在于当它遇到了AutoLayout之后其contentSize 的计算规则有些特殊。
contentSize是根据子视图的leading/trailing/top/bottom进行确定的

所以避免我们手动去设置 contentSize，我们必须迎合它的规则去设置

       let scrollView = UIScrollView()
        
        scrollView.backgroundColor = .gray
        view.addSubview(scrollView)
        scrollView.snp.makeConstraints { (make) in
            make.edges.equalToSuperview()
        }
        let containerView = UIView()
        containerView.backgroundColor = .blue
        scrollView.addSubview(containerView)
        containerView.snp.makeConstraints { (make) in
            make.edges.equalToSuperview()
            make.width.equalToSuperview()
        }
        
        let view1 = UIView()
        view1.backgroundColor = .orange
        
        let view2 = UIView()
        view2.backgroundColor = .blue
        
        
        containerView.addSubview(view1)
        containerView.addSubview(view2)
        
        view1.snp.makeConstraints { (make) in
            make.top.equalToSuperview()
            make.width.equalToSuperview()
            make.height.equalTo(500)
        }
        
        view2.snp.makeConstraints { (make) in
            make.top.equalTo(view1.snp.bottom)
            make.bottom.equalTo(containerView.snp.bottom)
            make.leading.trailing.equalTo(containerView)
            make.width.equalToSuperview()
            make.height.equalTo(500)
        }

大概就是这意思，我们通过一个填满的 containerView 去设置子视图，同时我们最后一个 subview 的 bottom 一定要与 containerView 对齐即可

来源https://segmentfault.com/a/1190000037456477