为什么多次调用 viewDidLayoutSubviews? [英] Why is viewDidLayoutSubviews called multiple times?

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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