我创建了一个自定义容器 Controller ，其工作方式与 UIPageViewController 类似，这样我就可以实现一些自定义转换和数据源逻辑。我尝试模仿新的客户 View Controller 转换 API 在 iOS 7 中的工作方式，它运行良好，除了在转换被取消时 View 外观回调有一些恼人的怪癖>...

即，在执行过渡时，究竟应该在什么时候调用 beginAppearanceTransition:animated: 和 endAppearanceTransition？

我的自定义容器类有一些这样的代码:

- (BOOL)shouldAutomaticallyForwardAppearanceMethods
{
    return NO;  // Since the automatic callbacks are wrong for our custom transition.
}

- (void)startTransition:(CustomTransitionContext *)context
{
    // Get reference to the view controllers involved in the transition.
    UIViewController *oldVC = [context viewControllerForKey:UITransitionContextFromViewController];
    UIViewController *newVC = [context UITransitionContextToViewController];
    
    // Prepare parent/child relationship changes.
    [oldVC willMoveToParentViewController:nil];
    [self addChildViewController:newVC];

    // Begin view appearance transitions.
    [oldVC beginAppearanceTransition:NO animated:[context isAnimated]];
    [newVC beginAppearanceTransition:YES animated:[context isAnimated]];
    
    // Register a completion handler to run when the context's completeTransition: method is called.
    __weak CustomContainerController *weakSelf = self;
    context.transitionCompletionHandler = ^(BOOL complete) {
        // End appearance transitions here?
        [oldVC endAppearanceTransition];
        [newVC endAppearanceTransition];

        if (complete) {
            // Or only if the transition isn't cancelled; here?
            [oldVC endAppearanceTransition];
            [newVC endAppearanceTransition];

            [oldVC removeFromParentViewController];
            [newVC didMoveToParentViewController:weakSelf];
        } else {
            [newVC removeFromParentViewController];
            [oldVC didMoveToParentViewController];
        }
    }

    if ([context isInteractive] && [self.transitionController conformsToProtocol:@protocol(UIViewControllerInteractiveTransitioning)]) {
        // Start the interactive transition.
        [self.transitionController startInteractiveTransition:context];
    } else if ([context isAnimated] && [self.transitionController conformsToProtocol:@protocol(UIViewControllerAnimatedTransitioning)]) {
        // Start the animated transition.
        [self.transitionController animateTransition:context];
    } else {
        // Just complete the transition.
        [context completeTransition:YES];
    }
}

所以如果我调用 endAppearanceTransition 而不管转换是否被取消，那么当转换被取消时我的 View 回调看起来像这样:

oldVC viewWillDisappear:  // Fine
newVC viewWillAppear:     // Fine
// ... some time later transition is cancelled ...
oldVC viewDidDisappear:   // Wrong! This view controller's view is staying.
newVC viewDidAppear:      // Wrong! The appearance of this view controllers view was cancelled.

如果我在转换成功完成时调用endAppearanceTransition仅，一开始看起来会更好:

oldVC viewWillDisappear:  // Fine
newVC viewWillAppear:     // Fine
// ... some time later transition is cancelled ...
// ... silence. (which is correct - neither view actually appeared or disappeared,
//               and I can undo side effects in viewWill(Dis)Appear using the 
//               transitionCoordinator object)

但是，下次我开始转换时，我没有收到 View 外观回调。下一组 View 外观回调仅在 beginAppearanceTransition:animated: 之后到达，随后是 endApperanceTransition 调用。值得注意的是，我没有收到经常报告的“对 ViewController 开始/结束外观转换的调用不平衡”控制台警告。

在WWDC 2013 Session 218 (Custom Transitions Using View Controllers) Bruce Nilo 开了一个相当中肯的玩笑，他的同事告诉他 viewWillAppear: & viewWillDisappear: 真的应该叫做 viewMightAppear: & viewMightDisappear: (请参阅该 session 从 42:00 开始的部分)。鉴于我们现在处于可取消交互手势的领域，似乎我们需要一个用于自定义容器的 cancelAppearanceTransition(或 endAppearanceTransition:(BOOL)finished)方法。

有人知道我做错了什么吗？或者自定义容器中的可取消自定义转换还没有得到正确支持？

最佳答案

因此，正如 SO 的常态一样，您花费数小时毫无结果地解决一个问题，然后在您发布问题后，您立即找到了答案...

我查看了 UINavigationController 的内置 interactivePopGestureRecognizer 的外观回调，看看取消转换时会发生什么，看来我对外观的假设应该调用的方法是错误的。

对于成功转换到的 View Controller ，会收到以下回调(如您所料):

                 transition
                  finished
viewWillAppear:  ---------->  viewDidAppear:

但是对于不成功的 View Controller 转换(即转换被取消)， View Controller 会收到以下回调:

                 transition                       immediately
                 cancelled                        followed by
viewWillAppear:  ---------->  viewWillDisappear:  ---------->  viewDidDisappear:

所以我们得到了更多那些狡猾的 View 外观语义；如果 View 还没有出现，我不确定 View 如何消失!哦好吧......我想这比一个 View 说它会出现，然后什么也没有发生要好一些。

因此，回到我的CustomTransitionContext 的transitionCompletionHandler 代码，解决方案如下所示:

...

// Register a completion handler to run when the context's completeTransition: method is called.
__weak CustomContainerController *weakSelf = self;
__weak CustomTransitionContext *weakContext = context;
context.transitionCompletionHandler = ^(BOOL complete) {
    if (complete) {
        // End the appearance transitions we began earlier.
        [oldVC endAppearanceTransition];
        [newVC endAppearanceTransition];

        [oldVC removeFromParentViewController];
        [newVC didMoveToParentViewController:weakSelf];
    } else {
        // Before ending each appearance transition, begin an
        // appearance transition in the opposite direction.
        [newVC beginAppearanceTransition:NO animated:[weakContext isAnimated]];
        [newVC endAppearanceTransition];
        [oldVC beginAppearanceTransition:YES animated:[weakContext isAnimated]];
        [oldVC endAppearanceTransition];

        [newVC removeFromParentViewController];
        [oldVC didMoveToParentViewController];
    }
}

....

所以现在外观回调看起来像这样:

oldVC viewWillDisappear:
newVC viewWillAppear:
// ... some time later transition is cancelled ...
newVC viewWillDisappear:
newVC viewDidDisappear:
oldVC viewWillAppear:
oldVC viewDidAppear:

此外，后续转换现在会按预期触发回调(因为我们通过调用 endAppearanceTransition 来关闭所有转换)。

关于ios - 如何 'cancel' 查看自定义容器 Controller 转换的外观转换，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21306496/