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我有一个 viewController，我正在使用锚点，我想获得一个按钮的框架。我只想要在视图被推送时的框架，所以我使用isMovingToParentViewController. 像这样：

if isMovingToParentViewController {

    let myButtonFrame = myButton.convert(myButton.bounds, to: self.view)
}

当我在viewWillAppear代码中添加它以使按钮的框架运行但当我向它添加相同的代码时viewDidLayoutSubviews它不会运行。

这是为什么？

只是为了清楚，viewDidLayoutSubviews当我添加一个断点时它确实命中if isMovingToParentViewController但其中的代码永远不会被命中。

当视图被推送到 isMovingToParentViewController上时，它会被击中，当它弹出时，isMovingToParentViewController不会被击中。

override func viewDidLoad() {
    super.viewDidLoad()

    // anchors are set here but the frames haven't been set yet
}

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

    if isMovingToParentViewController {

        // this code runs
        let myButtonFrame = myButton.convert(myButton.bounds, to: self.view)
    }
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    if isMovingToParentViewController {

        // this code NEVER runs
        let myButtonFrame = myButton.convert(myButton.bounds, to: self.view)
    }
}
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1 回答 1

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标头文档指出，isMovingToParentViewController其他 3 种方法仅在外观回调中有效，viewWillAppear因此在布局回调中无效，如viewDidLayoutSubviews.

/*
  These four methods can be used in a view controller's appearance callbacks to determine if it is being
  presented, dismissed, or added or removed as a child view controller. For example, a view controller can
  check if it is disappearing because it was dismissed or popped by asking itself in its viewWillDisappear:
  method by checking the expression ([self isBeingDismissed] || [self isMovingFromParentViewController]).
*/

#if UIKIT_DEFINE_AS_PROPERTIES
@property(nonatomic, readonly, getter=isBeingPresented) BOOL beingPresented NS_AVAILABLE_IOS(5_0);
@property(nonatomic, readonly, getter=isBeingDismissed) BOOL beingDismissed NS_AVAILABLE_IOS(5_0);

@property(nonatomic, readonly, getter=isMovingToParentViewController) BOOL movingToParentViewController NS_AVAILABLE_IOS(5_0);
@property(nonatomic, readonly, getter=isMovingFromParentViewController) BOOL movingFromParentViewController NS_AVAILABLE_IOS(5_0);
#else
- (BOOL)isBeingPresented NS_AVAILABLE_IOS(5_0);
- (BOOL)isBeingDismissed NS_AVAILABLE_IOS(5_0);

- (BOOL)isMovingToParentViewController NS_AVAILABLE_IOS(5_0);
- (BOOL)isMovingFromParentViewController NS_AVAILABLE_IOS(5_0);
#endif
于 2019-05-29T11:06:07.157 回答