对于 ViewController 的 'main' 视图，是否必须将 translatesAutoresizingMaskIntoConstraints 设置为 false？

Question

我在 Xcode 中有一个空白的 Swift 项目，我没有使用故事板。我有一个观点，我已经在 viewDidLoad:

下的代码中添加了

var view1 = UIView()
view1.backgroundColor = .red
view.addSubview(view1)
view1.translatesAutoresizingMaskIntoConstraints = false

然后我添加约束：

NSLayoutConstraint.activate([
            view1.topAnchor.constraint(equalTo: view.topAnchor, constant: 20),
            view1.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 20),
            view1.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -20),
            view1.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -20)
        ])

视图加载并在模拟器中看起来很好。但是我在另一个项目中遇到了一些其他视图的问题，所以我构建了上面的内容进行测试。所以我发现即使上面的构建和工作，如果我使用以下方法检查不明确的布局：

print(view1.hasAmbiguousLayout)

我记录了错误：

2021-02-14 15:26:34.919048+1100 autolayoutextensions[6603:4438601] [LayoutConstraints] View has an ambiguous layout. See "Auto Layout Guide: Ambiguous Layouts" for help debugging. Displaying synopsis from invoking -[UIView _autolayoutTrace] to provide additional detail.

*UIView:0x13360c3b0- AMBIGUOUS LAYOUT for UIView:0x13360c3b0.Width{id: 9}, UIView:0x13360c3b0.Height{id: 12}

Legend: * - is laid out with auto layout + - is laid out manually, but is represented in the layout engine because translatesAutoresizingMaskIntoConstraints = YES • - layout engine host true

让这些错误不被记录的唯一方法是同时设置 ViewController 的主视图，如下所示：

view.translatesAutoresizingMaskIntoConstraints = false

通过这样做，我知道得到以下日志输出：

false

所以我的问题是...我没有在 Apple 的文档（或此处，谷歌搜索等）中读到任何地方说您必须将 viewController 的 view.translatesAutoresizingMaskIntoConstraints 设置为 false。我错过了什么吗？抱歉，如果这只是我的理解，但最好能澄清一下。

Answer 1

首先，你不应该在视图控制器的主视图上设置 .translatesAutoresizingMaskIntoConstraints = false（除非你将控制器加载为 child，但这不是你在问题中谈论的内容） .

您需要 read-up 查看 / view-controller life-cycle.

在 viewDidLoad() 中，auto-layout 尚未运行管理视图和子视图布局。

在 viewDidLayoutSubview()、auto-layout HAS 运行中，但这可能取决于您的设计的动态程度（除其他因素外）调用不止一次。

在 viewDidAppear() 中，所有布局都已完成（除非您的代码正在运行对动画视图进行异步处理，添加其他视图，等等）。

所以，试试运行这个简单的例子 - 它会打印当前正在执行的函数的名称以及 .hasAmbiguousLayout:

的输出

class TestLayoutViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        var view1 = UIView()
        view1.backgroundColor = .red
        view.addSubview(view1)
        view1.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activate([
            view1.topAnchor.constraint(equalTo: view.topAnchor, constant: 20),
            view1.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 20),
            view1.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -20),
            view1.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -20)
        ])
        
        print() // blank line
        print(#function)
        print() // blank line
        print("In viewDidLoad(), does subview have ambigous layout?")
        print(view1.hasAmbiguousLayout)

    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        
        guard let v = view.subviews.first else {
            return
        }
        
        print() // blank line
        print(#function)
        print() // blank line
        print("In viewDidLayoutSubviews(), does subview have ambigous layout?")
        print(v.hasAmbiguousLayout)
        
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        guard let v = view.subviews.first else {
            return
        }
        
        print() // blank line
        print(#function)
        print() // blank line
        print("In viewDidAppear(), does subview have ambigous layout?")
        print(v.hasAmbiguousLayout)
        
    }
    
}

这是您应该在调试控制台中看到的内容：

viewDidLoad()

In viewDidLoad(), does subview have ambigous layout?
2021-02-14 08:41:46.694337-0500 PanZoom[43869:6978294] [LayoutConstraints] View has an ambiguous layout. See "Auto Layout Guide: Ambiguous Layouts" for help debugging. Displaying synopsis from invoking -[UIView _autolayoutTrace] to provide additional detail.

*UIView:0x7fd472604960- AMBIGUOUS LAYOUT for UIView:0x7fd472604960.Width{id: 90}, UIView:0x7fd472604960.Height{id: 93}

Legend:
    * - is laid out with auto layout
    + - is laid out manually, but is represented in the layout engine because translatesAutoresizingMaskIntoConstraints = YES
    • - layout engine host
true

viewDidLayoutSubviews()

In viewDidLayoutSubviews(), does subview have ambigous layout?
false

viewDidAppear(_:)

In viewDidAppear(), does subview have ambigous layout?
false

如您所见，在 viewDidLoad() 期间我们得到 auto-layout 歧义，但 NOT 在 viewDidLayoutSubviews() 或 viewDidAppear().

对于 ViewController 的 'main' 视图，是否必须将 translatesAutoresizingMaskIntoConstraints 设置为 false？

Do you have to set translatesAutoresizingMaskIntoConstraints to false for a ViewController's 'main' view?

ios

autolayout

swift