ios - willMoveToWindow 被调用两次

Question

我在调整 willMoveToWindow: 时遇到一个问题，它在 View 上被调用了两次。

当一个新的 View Controller 被推送到一个 UINavigationController 上时，

willMoveToWindow: 在具有 nil 值的现有 View 上调用(有意义，因为 View 正在移出屏幕)

在那之后，方法 willMoveToWindow: 被再次调用，但现在与原始窗口一起调用。

我最初的想法是在原始方法开始之前调配并调用 window 属性。

为了安全起见，我创建了一个小型示例项目并确认了相同的行为。

基本上我需要一种方法来确定 View 不在 window 上(因为当 View 移动到实际上不应该运行的窗口时我正在触发逻辑(在至少不是两次))

作为引用，可以使用以下代码重现该问题:

  @implementation RandomView

    -(void)willMoveToWindow:(UIWindow *)newWindow {
    // when the new view controller is pushed - 
    //the method is called twice on the existing view (on the screen view)- 
    //first time will be called with nil - 
    //second time with the original window
        NSLog(@"********%s <RandomView %p> <Window %p>",__PRETTY_FUNCTION__,self,newWindow);
    }

    -(void)didMoveToWindow {
        NSLog(@"********%s <RandomView %p> <Window %p>",__PRETTY_FUNCTION__,self,self.window);
    }
    @end

    @implementation ViewController

    - (void)viewDidLoad {
        [super viewDidLoad];
        RandomView *k = [[RandomView alloc] initWithFrame:self.view.bounds];
        [self.view addSubview:k];
    }


    -(void)viewDidAppear:(BOOL)animated {
        [super viewDidAppear:animated];
        static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                ViewController *vc = [[ViewController alloc] init];
                [self.navigationController pushViewController:vc animated:YES];
            });
        });

        //[self becomeFirstResponder];
    }
    @end

编辑控制台

    [RandomView willMoveToWindow:] <RandomView 0x7f8b21e16630> <Window 0x7f8b21d220d0>
    [RandomView didMoveToWindow] <RandomView 0x7f8b21e16630> <Window 0x7f8b21d220d0>
  //THIS IS THE ISSUE
    [RandomView willMoveToWindow:] <RandomView 0x7f8b21e16630> <Window 0x0>
    [RandomView didMoveToWindow] <RandomView 0x7f8b21e16630> <Window 0x0>
    [RandomView willMoveToWindow:] <RandomView 0x7f8b21e16630> <Window 0x7f8b21d220d0>
    [RandomView didMoveToWindow] <RandomView 0x7f8b21e16630> <Window 0x7f8b21d220d0>

    [RandomView willMoveToWindow:] <RandomView 0x7f8b21e16630> <Window 0x0>
    [RandomView didMoveToWindow] <RandomView 0x7f8b21e16630> <Window 0x0>

Answer 1

我也遇到了同样的问题

但在通过响应链查找 View 层次结构后，有一个小的不同可以检查。我不确定这是否安全。

但我认为 Apple 以错误的顺序执行动画代码，如果他们先将动画 View 添加到窗口，willMoveToWindow: 将不会调用两次。

2017-03-08 22:49:35.167 view[36189:410065] show
0x7fa9c36059f0,MyView
0x7fa9c3407cb0,UIView
0x7fa9c340b9d0,ViewController
0x7fa9c3403c50,UIViewControllerWrapperView
0x7fa9c340ee90,UINavigationTransitionView
0x7fa9c5802d10,UILayoutContainerView
0x7fa9c381ee00,UINavigationController
0x7fa9c3609c40,UIWindow
0x7fa9c3400020,UIApplication
0x608000038900,AppDelegate
2017-03-08 22:49:54.501 view[36189:410065] hide
0x7fa9c36059f0,MyView
0x7fa9c3407cb0,UIView
0x7fa9c340b9d0,ViewController
0x7fa9c3500bd0,UIView  <----- not real hide
2017-03-08 22:49:54.501 view[36189:410065] show
0x7fa9c36059f0,MyView
0x7fa9c3407cb0,UIView
0x7fa9c340b9d0,ViewController
0x7fa9c3500bd0,UIView
0x7fa9c3403c50,UIViewControllerWrapperView
0x7fa9c340ee90,UINavigationTransitionView
0x7fa9c5802d10,UILayoutContainerView
0x7fa9c381ee00,UINavigationController
0x7fa9c3609c40,UIWindow
0x7fa9c3400020,UIApplication
0x608000038900,AppDelegate
2017-03-08 22:49:54.501 view[36189:410065] show
0x7fa9c35062f0,MyView
0x7fa9c3505ae0,UIView
0x7fa9c58030c0,ViewController
0x7fa9c3506c10,_UIParallaxDimmingView
0x7fa9c35022c0,UIView
0x7fa9c3403c50,UIViewControllerWrapperView
0x7fa9c340ee90,UINavigationTransitionView
0x7fa9c5802d10,UILayoutContainerView
0x7fa9c381ee00,UINavigationController
0x7fa9c3609c40,UIWindow
0x7fa9c3400020,UIApplication
0x608000038900,AppDelegate
2017-03-08 22:49:55.037 view[36189:410065] hide
0x7fa9c36059f0,MyView
0x7fa9c3407cb0,UIView
0x7fa9c340b9d0,ViewController  <----- real hide