检测视图控制器何时从弹出窗口出现

Question

我在导航堆栈深处弹出一个视图控制器。是否可以检测视图控制器是从推送还是弹出显示？

nav stack:

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

[E] 弹出到 [B]

nav stack:

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

Answer 1

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

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
    }
}

以下是人们可能会觉得方便的这些属性的更一般用法：

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
    }
}