NSLayoutConstraint-无法将子视图框架设置为父视图范围

Question

我有一个testView UIView和名为testViewSub的子视图。 使用NSLayoutConstraint限制了NSLayoutConstraint 。 我将subView框架设置为testView.bounds 。 但这是行不通的。 这是代码

let testView = UIView()
    testView.backgroundColor = UIColor.red

    self.view.addSubview(testView)

    testView.translatesAutoresizingMaskIntoConstraints = false


    NSLayoutConstraint(item: testView, attribute: .leading, relatedBy: .equal, toItem: self.view, attribute: .leading, multiplier: 1.0, constant: 30).isActive = true

    NSLayoutConstraint(item: testView, attribute: .trailing, relatedBy: .equal, toItem: self.view, attribute: .trailing, multiplier: 1.0, constant: -30).isActive = true

    NSLayoutConstraint(item: testView, attribute: .top, relatedBy: .equal, toItem: self.view, attribute: .top, multiplier: 1.0, constant: 200).isActive = true

    NSLayoutConstraint(item: testView, attribute: .height, relatedBy: .equal, toItem: self.view, attribute: .height, multiplier: 0.15, constant: 0).isActive = true




    let testViewSub = UIView()
    testViewSub.backgroundColor = UIColor.green
    testViewSub.frame = testView.bounds
    self.testView.addSubview(testViewSub)

    testViewSub.translatesAutoresizingMaskIntoConstraints = false

但是如果我使用CGRect设置testView的框架。 有用。

Answer 1

布局在哪里发生？ 在出现约束之前，我一直遇到问题，直到视图出现，约束才生效，因此依赖于viewWillAppear在viewDidLoad或viewWillAppear的正确大小会引起问题。

在这种情况下，在viewDidAppear添加testViewSub对我testViewSub ，尽管我不确定这是我推荐的方式。 与testView ，使用约束进行布局也可以在viewDidLoad或viewWillAppear ：

    // layout constraints however you want - in this case they are such that green view's frame = red view's bounds

    let testViewSub = UIView()
    testViewSub.backgroundColor = UIColor.green
    self.testView.addSubview(testViewSub)

    NSLayoutConstraint(item: testViewSub, attribute: .leading, relatedBy: .equal, toItem: testView, attribute: .leading, multiplier: 1.0, constant: 0).isActive = true

    NSLayoutConstraint(item: testViewSub, attribute: .trailing, relatedBy: .equal, toItem: testView, attribute: .trailing, multiplier: 1.0, constant: 0).isActive = true

    NSLayoutConstraint(item: testViewSub, attribute: .top, relatedBy: .equal, toItem: testView, attribute: .top, multiplier: 1.0, constant: 0).isActive = true

    NSLayoutConstraint(item: testViewSub, attribute: .height, relatedBy: .equal, toItem: testView, attribute: .height, multiplier: 1.0, constant: 0).isActive = true


    testViewSub.translatesAutoresizingMaskIntoConstraints = false

与简单地设置框架相比，这还将更好地处理旋转。