检测何时从弹出窗口显示视图控制器 [英] Detect when view controller appears from pop

问题描述

我正在将视图控制器弹出到导航堆栈的深处。

I am popping a view controller deep within a navigation stack. Is it possible to detect if the view controller is being shown from a push or a pop?

nav stack:

[A] -> [B] -> [C] -> [D] -> [E]

[E]弹出[B]

nav stack:

[A]  -> [B] // Possible to detect if B appears from a pop?

推荐答案

在视图控制器B中，实现 viewWillAppear 或 viewDidAppear 。在其中，使用 isMovingToParent 和 isBeingPresented 来查看它在什么条件下出现：

In view controller B, implement either viewWillAppear or viewDidAppear. In there, use isMovingToParent and isBeingPresented to see under what conditions it is appearing:

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

    if !isBeingPresented && !isMovingToParent {
        // this view controller is becoming visible because something that was covering it has been dismissed or popped
    }
}

以下是人们可能会方便使用的这些属性的更一般用法：

Below is a more general use of these properties that people may find handy:

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

    if isMovingToParent {
        // this view controller is becoming visible because it was just push onto a navigation controller or some other container view controller
    } else if isBeingPresented {
        // this view controller is becoming visible because it is being presented from another view controller
    } else if view.window == nil {
        // this view controller is becoming visible for the first time as the window's root view controller
    } else {
        // this view controller is becoming visible because something that was covering it has been dismissed or popped
    }
}

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