如何“取消”自定义容器控制器转换的视图外观转换

Question

我创建了一个与UIPageViewController类似的自定义容器控制器，这样我就可以实现一些自定义转换＆amp;数据源逻辑。我尝试模仿新客户视图控制器转换API在iOS 7中的工作方式，并且除了在转换 取消时的视图外观回调时出现一些令人恼火的怪癖 ...

即，在执行转换时，何时应该调用beginAppearanceTransition:animated:和endAppearanceTransition？

---

我的自定义容器类有一些代码如下：

- (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];
    }
}

因此，如果我调用endAppearanceTransition而不管转换是否被取消，那么当取消转换时，我的视图回调看起来像这样：

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后只调用endAppearanceTransition ，那么事情看起来会更好：

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，我收到没有视图外观回调。下一组视图外观回调仅在beginAppearanceTransition:animated:后跟endApperanceTransition调用后到达。值得注意的是，我不收到经常报告的“对ViewController 开始/结束外观转换的不平衡调用”控制台警告。

在WWDC 2013 Session 218 (Custom Transitions Using View Controllers)布鲁斯·尼洛（Bruce Nilo）对他的同事们说了viewWillAppear:＆amp; viewWillDisappear:确实应该被称为viewMightAppear:＆amp; viewMightDisappear: （请参阅从42:00开始的该会话部分）。鉴于我们现在处于可取消的交互式手势领域，我们似乎需要cancelAppearanceTransition（或endAppearanceTransition:(BOOL)finished）方法来定制容器。

有人知道我做错了什么吗？或者是可取消的，自定义容器中的自定义转换尚未正确支持？

Answer 1

因此，通常采用SO的方式，你花费数小时无效地解决问题，然后在你发布问题后，你就会找到答案......

我查看了UINavigationController内置interactivePopGestureRecognizer的外观回调，看看取消转换时会发生什么，看来我对外观方法应该< / em>被称为错误。

对于成功转换到的视图控制器，会收到以下回调（正如您所期望的那样）：

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

但是对于不成功的视图控制器转换（即转换被取消），视图控制器会收到以下回调：

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

所以我们得到了更多那些狡猾的视图外观语义;我不确定视图如何消失如果还没有出现！哦，好吧......我认为它比一个说明会出现，然后什么都没发生的观点要好一些。

因此，返回我的CustomTransitionContext的{​​{1}}代码，解决方案如下所示：

transitionCompletionHandler

所以现在外观回调看起来像这样：

...

// 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];
    }
}

....

此外，后续转换现在会按预期触发回调（因为我们通过调用oldVC viewWillDisappear: newVC viewWillAppear: // ... some time later transition is cancelled ... newVC viewWillDisappear: newVC viewDidDisappear: oldVC viewWillAppear: oldVC viewDidAppear: 来关闭所有转换）。