如何确定第一次启动UIViewController？ [英] How to determine that UIViewController was started for the first time?

问题描述

我有一个ViewControllers层次结构，UINavigationViewController作为根。

如何找出一些ViewController是第一次启动还是由于导航堆栈的展开而启动？

I have a ViewControllers hierarchy, with UINavigationViewController as the root.
How can I find out whether some ViewController was started for the first time or it was started as a result of unwinding of the navigation stack?

推荐答案

假设你想知道 viewWillAppear：（或 viewDidAppear：）在首次显示视图控制器时被调用，或者由于另一个视图控制器被解除而被显示，您可以轻松执行以下操作：

Assuming you wish to know if viewWillAppear: (or viewDidAppear:) is being called when the view controller is first being displayed or if it's being displayed because another view controller has been dismissed, you can easily do the following:

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)

    if isBeingPresented() || isMovingToParentViewController() {
        // This is the first time this instance of the view controller will appear
    } else {
        // This controller is appearing because another was just dismissed
    }
}

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