Autolayout

子元素隐藏

• 禁止子元素超出父元素高度
• 父元素设置：

clipsToBounds = YES

动态加约束

• 代码添加多个元素的相互约束需要添加：

// subview 需添加约束元素本身
blueBtn.translatesAutoresizingMaskIntoConstraints = false;

blueBtn.widthAnchor.constraint(equalToConstant: 200).isActive = true;

blueBtn.leadingAnchor.constraint(equalTo: blueView.leadingAnchor, constant: 100).isActive = true;

• 集体生效

let btnLeading = blueBtn.leadingAnchor.constraint(equalTo: blueView.leadingAnchor, constant: 100);
let btnTop = blueBtn.bottomAnchor.constraint(equalTo: blueView.bottomAnchor, constant: 100);
let btnBottom = blueBtn.topAnchor.constraint(equalTo: blueView.topAnchor, constant: 100);
NSLayoutConstraint.activate([btnLeading, btnTop, btnBottom]);

动态添加元素

• 子元素的x/y是依照在父元素的边界实现的

let btn1 = UIButton(frame: CGRect(x: 200, y: 100, width: 100, height: 100));
btn1.setTitle("哈哈哈", for: UIControl.State.normal);
blueView.addSubview(btn1);
btn1.backgroundColor = UIColor.blue;

设置动态添加元素附着点

// 设置附着view
pickerView?.popoverPresentationController?.sourceView = self.datePickView

// 设置附着元素
pickerView?.popoverPresentationController?.sourceRect = self.datePickerButton.frame

动态改变优先级

redHeight0.priority = redHeight0.priority.rawValue < 201 ? UILayoutPriority(rawValue: 1000.0) : UILayoutPriority(rawValue: 200.0)

动态改变滚动高度

• ScrollView控制顶部、底部距离为固定值，中间子盒子一个一个撑起ScrollView
  • 设置ScrollView与父盒子/兄弟上下左右的高度属性，priority设置最高
  • scrollView设置与子View的top相等，子View的bottom相等
  • ScrollView与子View的bottom的priority设置低一点
• tableView？

断点调试

po self.contentScrollView

获取指定元素距离顶部的距离

// 获取【相对于父元素】位置
let offsetY = deepBlueView.frame.origin.y

// scrollView 滚动到指定位置
self.contentScrollView.contentOffset = CGPoint.init(x: 0, y: offsetY)