为什么多次调用 viewDidLayoutSubviews?

问题描述

我正在使用 Swift 开发 iOS 通用应用程序，使用自动布局并且仅支持纵向.

I'm developing iOS Universal App with Swift, using auto layout and support only portrait.

我发现 UIViewController.viewDidLayoutSubviews 被调用了多次.相反，viewDidLoad 仅在启动 MyApp 的 UIViewController 时调用一次.

I found UIViewController.viewDidLayoutSubviews called multiple times. Instead, viewDidLoad is only called once on starting up MyApp's UIViewController.

为什么会多次调用viewDidLayoutSubviews?每个UIView(UIButtons、UITextFields等)的约束会按顺序执行吗?

Why is viewDidLayoutSubviews called multiple times? Will constraints on each UIView (UIButtons,UITextFields, etc..) be performed in order?

任何信息将不胜感激.

推荐答案

LoadView 只调用一次:当需要加载视图时.

LoadView is only called once: when the view needs to be loaded.

LayoutSubviews 在任何调用了 setNeedsLayout 或 setNeedsDisplayInRect 的视图上，每次运行循环都会调用一次 - 这包括任何时候视图中添加了子视图，可以滚动、调整大小等.

LayoutSubviews, however, is called once per run loop on any view that has had setNeedsLayout or setNeedsDisplayInRect called on it - this includes whenever a subview has been added to the view, scrolling, resizing, etc.

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