根据子视图自动设置容器视图的高度

Question

我知道这个问题已被问过无数次，但我似乎无法完全解决这个问题。

使用自动布局，我想根据它的子视图自动设置我的容器UIView的高度。我已经看过使用sizeToFit和其他各种方法来总结我的子视图的高度，但从我读过的高度来看，使用自动布局时，我的容器高度应该是自动的，因为子视图“内在”内容大小。

下面是我遇到的一个简化案例。我会很感激任何指导！

概述：

1. 创建容器的UIView，销到左，上海华盈的右侧，没有明确的高度，对准其centerY与它的父centerY
2. 创建300宽度100高度的UIView，添加它作为容器视图的子视图，将其centerX与容器视图的centerX对齐，将其与容器视图的顶部边缘对齐
3. 重复步骤2，除了这次将其顶部固定到＃2的底部边缘
4. 容器视图的预期高度是200，除了它的高度是a ctually仍为0（为此centerY对齐关闭）

代码：

class ViewController: UIViewController { 

    let redView = RedView() 

    override func viewDidLoad() { 
     super.viewDidLoad() 

     view.addSubview(redView) 
     view.setNeedsUpdateConstraints() 
    } 

} 

class RedView: UIView { 

    let greenView = GreenView() 
    let blueView = BlueView() 

    init() { 
     super.init(frame: CGRect.zero) 

     translatesAutoresizingMaskIntoConstraints = false 
     backgroundColor = UIColor.red() 

     addSubview(greenView) 
     addSubview(blueView) 
     setNeedsUpdateConstraints() 
    } 

    override func updateConstraints() { 
     super.updateConstraints() 

     NSLayoutConstraint(item: greenView, attribute: .top, relatedBy: .equal, toItem: self, attribute: .top, multiplier: 1, constant: 0).isActive = true 
     NSLayoutConstraint(item: blueView, attribute: .top, relatedBy: .equal, toItem: greenView, attribute: .bottom, multiplier: 1, constant: 0).isActive = true 

     NSLayoutConstraint(item: self, attribute: .left, relatedBy: .equal, toItem: superview, attribute: .left, multiplier: 1, constant: 0).isActive = true 
     NSLayoutConstraint(item: self, attribute: .right, relatedBy: .equal, toItem: superview, attribute: .right, multiplier: 1, constant: 0).isActive = true 
     NSLayoutConstraint(item: self, attribute: .centerY, relatedBy: .equal, toItem: superview, attribute: .centerY, multiplier: 1, constant: 0).isActive = true 
     NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 200).isActive = true 
    } 

} 

class GreenView: UIView { 

    init() { 
     super.init(frame: CGRect.zero) 

     translatesAutoresizingMaskIntoConstraints = false 
     backgroundColor = UIColor.green() 
    } 

    override func updateConstraints() { 
     super.updateConstraints() 

     NSLayoutConstraint(item: self, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 300).isActive = true 
     NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 100).isActive = true 
     NSLayoutConstraint(item: self, attribute: .centerX, relatedBy: .equal, toItem: superview, attribute: .centerX, multiplier: 1, constant: 0).isActive = true 
    } 

} 

class BlueView: UIView { 

    init() { 
     super.init(frame: CGRect.zero) 

     translatesAutoresizingMaskIntoConstraints = false 
     backgroundColor = UIColor.blue() 
    } 

    override func updateConstraints() { 
     super.updateConstraints() 

     NSLayoutConstraint(item: self, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 300).isActive = true 
     NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 100).isActive = true 
     NSLayoutConstraint(item: self, attribute: .centerX, relatedBy: .equal, toItem: superview, attribute: .centerX, multiplier: 1, constant: 0).isActive = true 
    } 

} 

Answer 1

你需要引脚蓝景的底部redView的底部，只是加入这一行redView的updateConstraints：

NSLayoutConstraint(item: blueView, attribute: .bottom, relatedBy: .equal, toItem: self, attribute: .bottom, multiplier: 1, constant: 0).active = true