UINavigationController 执行事务时发生崩溃答案

【问题标题】：Crash happened when UINavigationController doing transactionUINavigationController 执行事务时发生崩溃
【发布时间】：2014-07-16 20:22:37
【问题描述】：

我刚刚遇到如下截图所示的崩溃，当我点击导航栏上的返回按钮时发生了这种情况，是否有任何典型情况会导致这种崩溃？

【问题讨论】：

标签： ios objective-c uinavigationcontroller

【解决方案1】：

根据我的经验，iOS 7 中引入了一个问题，使您可以在另一个过渡结束之前开始过渡，这最终导致了这次崩溃。如果您将 2 个导航调用背靠背并运行它们，则可以手动重现此操作，例如：

[self.navigationController pushViewController:whatever animated:YES];
[self.navigationController pushViewController:whatever2 animated:YES];

如果你这样做，你最终会看到崩溃发生。

我发现确保这种情况永远不会发生的最简单方法是继承 UINavigationController 并实现 UINavigationControllerDelegate 以防止重叠转换。

一旦我开始使用下面的代码，我看到的由于此问题而导致的崩溃次数已降至 0。

需要注意的一点是，如果您确实需要实现另一个 <UINavigationControllerDelegate>，您将需要编写一些代码来自己存储额外的委托并传递委托调用，可能使用 NSProxy 或类似的东西。

@interface MyNavigationController () <UINavigationControllerDelegate>
{
    // used to prevent "can't add self as subview" crashes which occur when trying to animate 2 transitions simultaneously
    BOOL _currentlyAnimating;
}

@end

@implementation MyNavigationController

- (void) viewDidLoad
{
    [super viewDidLoad];
    self.delegate = self;
}

- (void) pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    if(_currentlyAnimating)
    {
        return;
    }
    else if(animated)
    {
        _currentlyAnimating = YES;
    }

    [super pushViewController:viewController animated:animated];
}

- (UIViewController *) popViewControllerAnimated:(BOOL)animated
{
    if(_currentlyAnimating)
    {
        return nil;
    }
    else if(animated)
    {
        _currentlyAnimating = YES;
    }

    return [super popViewControllerAnimated:animated];

}

- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    _currentlyAnimating = NO;
}

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    // tracking cancelled interactive pop
    // http://stackoverflow.com/questions/23484310/canceling-interactive-uinavigationcontroller-pop-gesture-does-not-call-uinavigat
    [[self transitionCoordinator] notifyWhenInteractionEndsUsingBlock:^(id<UIViewControllerTransitionCoordinatorContext> context)
    {
        if([context isCancelled])
        {
            UIViewController *fromViewController = [context viewControllerForKey:UITransitionContextFromViewControllerKey];
            [self navigationController:navigationController willShowViewController:fromViewController animated:animated];

            if([self respondsToSelector:@selector(navigationController:didShowViewController:animated:)])
            {
                NSTimeInterval animationCompletion = [context transitionDuration] * [context percentComplete];

                dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (uint64_t)animationCompletion * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
                    [self navigationController:navigationController didShowViewController:fromViewController animated:animated];
                });
            }


        }
    }];
}

@end

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