一个模拟推送Segue的自定义Segue将VC变成Zombie [英] a Custom Segue that Simulates a Push Segue turns VC into Zombie

问题描述

我写了一个自定义的segue。

I've written a custom segue.

-(void)perform {
UIView *preV = ((UIViewController *)self.sourceViewController).view;
UIView *newV = ((UIViewController *)self.destinationViewController).view;

[preV.window insertSubview:newV aboveSubview:preV];
newV.center = CGPointMake(preV.center.x + preV.frame.size.width, newV.center.y);
[UIView animateWithDuration:0.4
 animations:^{
     newV.center = CGPointMake(preV.center.x, newV.center.y);
     preV.center = CGPointMake(0- preV.center.x, newV.center.y);}
    completion:^(BOOL finished){ [preV removeFromSuperview]; }];
}

当触发segue时，没有异常。但是它会解除分配 destinationViewController 。

When the segue is triggered there is no exception. However it would deallocate destinationViewController.

当点击 destinationViewController 中触发另一个segue的按钮时，应用程序会崩溃。

The app would crash when a button, that triggers another segue, in destinationViewController is clicked.

我尝试删除 [preV removeFromSuperview] 但无济于事。

I tried removing [preV removeFromSuperview] but to no avail.

我最近开始使用Object-C，并编写了一个模拟推送segue的自定义segue。

I've recently started working with Object-C and I wrote a custom segue that simulates a push segue.

第一次被触发时，一切正常。

The first time it is been triggered, everything works fine.

但在那之后，无论触发了什么segue，
应用程序崩溃，我会收到 EXC_BAD_ACCESS 错误。

But after that, no matter what segue is been triggered, the app crashes and I would receive a EXC_BAD_ACCESS error.

我的第一个猜测是这与内存管理有关。那里的东西必须要解除分配，但我不知道它是什么。

My first guess is that this has to do with memory management. Something out there has to be deallocated but I have no idea what it is.

我的第二个猜测是，这与 UIView 和 UIWindow 。但是再一次，由于我缺乏知识和经验，我无法弄清楚真正的问题是什么。

My second guess is that this has to do with the infrastructure provided by UIView and UIWindow . But once again, due to my lack of knowledge and experience, I can't figure out what the real problem is.

我知道我实际上可以采取一种简单的方法通过使用 rootviewcontroller 创建一个推送segue并简单地隐藏导航栏，但我真的想知道我看似构造良好的自定义segue究竟出了什么问题，并了解什么是在代码结构下面进行。

I know I can actually take an easy approach and create a push segue by using a rootviewcontroller and simply hiding the navigation bar, but I really want to know what exactly is wrong with my seemingly well-constructed custom segue and learn what is going on underneath the fabric of codes.

感谢Phillip Mills& Joachim Isaksson的建议，在进行了一些实验并利用断点和僵尸工具之后，

Thank Phillip Mills & Joachim Isaksson for the suggestions, after conducting some experiments and making use of breakpoints and the Zombie tool,

这是我意识到的：

1. 在按钮触发自定义segue后，应用程序只会在按钮触发下一个segue时崩溃。使用 viewDidAppear 触发下一个segue不会导致任何崩溃。

1. After the custom segue has been triggered by a button,the app would only crash when the next segue is also triggered by a button. Triggering the next segue using viewDidAppear would not lead to any crash.

崩溃背后的主要原因：

将Objective-C邮件发送到已解除分配的对象（僵尸）

[＃，事件类型，refCt，图书馆，来电者]

[#, event type, refCt, Library, Caller]

0   Malloc  1   UIKit   -[UIClassSwapper initWithCoder:]
1   Retain  2   UIKit   -[UIRuntimeConnection initWithCoder:]
2   Retain  3   UIKit   -[UIRuntimeConnection initWithCoder:]
3   Retain  4   UIKit   -[UIRuntimeConnection initWithCoder:]
4   Retain  5   UIKit   -[UIRuntimeConnection initWithCoder:]
5   Retain  6   UIKit   -[UIRuntimeConnection initWithCoder:]
6   Retain  7   UIKit   -[UIRuntimeConnection initWithCoder:]
7   Retain  8   UIKit   -[UIRuntimeConnection initWithCoder:]
8   Retain  9   UIKit   UINibDecoderDecodeObjectForValue
9   Retain  10  UIKit   UINibDecoderDecodeObjectForValue
10  Retain  11  UIKit   -[UIStoryboardScene setSceneViewController:]
11  Retain  12  UIKit   -[UINib instantiateWithOwner:options:]
12  Release 11  UIKit   -[UINibDecoder finishDecoding]
13  Release 10  UIKit   -[UINibDecoder finishDecoding]
14  Release 9   UIKit   -[UIRuntimeConnection dealloc]
15  Release 8   UIKit   -[UIRuntimeConnection dealloc]
16  Release 7   UIKit   -[UIRuntimeConnection dealloc]
17  Release 6   UIKit   -[UIRuntimeConnection dealloc]
18  Release 5   UIKit   -[UINibDecoder finishDecoding]
19  Release 4   UIKit   -[UIRuntimeConnection dealloc]
20  Release 3   UIKit   -[UIRuntimeConnection dealloc]
21  Release 2   UIKit   -[UIRuntimeConnection dealloc]
22  Retain  3   UIKit   -[UIStoryboardSegue initWithIdentifier:source:destination:]
23  Retain  4   ProjectX    -[pushlike perform]
24  Retain  5   UIKit   -[UINib instantiateWithOwner:options:]
25  Retain  6   UIKit   +[UIProxyObject addMappingFromIdentifier:toObject:forCoder:]
26  Retain  7   UIKit   -[UIProxyObject initWithCoder:]
27  Retain  8   UIKit   -[UIRuntimeConnection initWithCoder:]
28  Retain  9   UIKit   UINibDecoderDecodeObjectForValue
29  Retain  10  UIKit   UINibDecoderDecodeObjectForValue
30  Release 9   UIKit   -[UINib instantiateWithOwner:options:]
31  Release 8   UIKit   +[UIProxyObject removeMappingsForCoder:]
32  Release 7   UIKit   -[UINibDecoder finishDecoding]
33  Release 6   UIKit   -[UIRuntimeConnection dealloc]
34  Release 5   UIKit   -[UINibDecoder finishDecoding]
35  Release 4   UIKit   -[UINibDecoder finishDecoding]
36  Release 3   ProjectX    -[pushlike perform]
37  Retain  4   libsystem_sim_blocks.dylib  _Block_object_assign
38  Retain  5   UIKit   -[UIApplication _addAfterCACommitBlockForViewController:]
39  Release 4   UIKit   -[UIStoryboardSegue dealloc]
40  Release 3   UIKit   _UIApplicationHandleEvent
41  Release 2   UIKit   -[UIStoryboardScene dealloc]
42  Retain  3   UIKit   _applyBlockToCFArrayCopiedToStack
43  Release 2   UIKit   _applyBlockToCFArrayCopiedToStack
44  Release 1   UIKit   __destroy_helper_block_739
45  Release 0   UIKit   _applyBlockToCFArrayCopiedToStack
46  Zombie  -1  UIKit   -[UIApplication sendAction:to:from:forEvent:]

这意味着（如果我没有错误）

自定义segue以某种方式触发了释放对象的内容，按钮后会发送一条Objective-C消息（在 destinationViewController 中）点击触发另一个segue。

the custom segue has somehow triggered something that deallocates objects, to which an objective-C message would be sent after button (in destinationViewController) that triggers another segue is clicked.

由于我不需要在视图之间传递数据，因此没有调用 prepareForSegue 。

Not a single prepareForSegue is been called since I don't need to pass data between views.

我的segues都以相同的方式触发：

My segues are all triggered the same way:

- (void)viewDidLoad
{
    [super viewDidLoad];
    CGRect buttonFrame = CGRectMake( 10, 40, 200, 50 );
    UIButton *button = [[UIButton alloc] initWithFrame: buttonFrame];
    [button setTitle: @"Go" forState: UIControlStateNormal];
    [button addTarget:self action:@selector(nextView) forControlEvents:UIControlEventTouchUpInside];
    [button setTitleColor: [UIColor blackColor] forState: UIControlStateNormal];
    [self.view addSubview:button]; 
}

- (void)nextView{
    [self performSegueWithIdentifier:@"push" sender:self];
}

我启用了ARC，所以我没有真正做任何解除分配我自己..

I have my ARC enabled so I didn't really do any of the deallocation myself..

[更新2]

已经变成僵尸的对象是自定义segue的 destinationViewController 。

The object that has been turned into a zombie is the destinationViewController of the custom segue.

在自定义segue中不调用 removeFromSuperview 不会阻止对象变成僵尸。

Not calling removeFromSuperview in the custom segue does not stop the object from turning into zombie.

只要我使用一个普通的模型segue或push segue（用rootViewController）而不是我自己制作的那个，不会有任何僵尸，一切都会正常工作。

As long as I use a regular model segue or a push segue (with rootViewController) instead the custom one I made, there won't be any zombie and everything would work fine.

推荐答案

你的崩溃只是因为你的新控制器在segue执行后没有保留。

You're getting a crash just because your new controller not retained after segue execution.

你做的是：

• src和dest控制器被实例化


• 你执行你的动画


• in完成删除src视图


• 哟你的src控制器被释放了，但是窗口的 rootViewController 仍然指向它并且你的目标视图控制器不被添加到窗口的层次结构中。

• src and dest controllers are instantiated
• you perform your animations
• in completion you remove src view
• your src controller gets released, but window's rootViewController still pointing to it and your destination view controller not added to window's hierarchy.

这将按预期工作：

-(void)perform {
  UIView *preV = ((UIViewController *)self.sourceViewController).view;
  UIView *newV = ((UIViewController *)self.destinationViewController).view;

  UIWindow *window = [[[UIApplication sharedApplication] delegate] window];
  newV.center = CGPointMake(preV.center.x + preV.frame.size.width, newV.center.y);
  [window insertSubview:newV aboveSubview:preV];

  [UIView animateWithDuration:0.4
                   animations:^{
                       newV.center = CGPointMake(preV.center.x, newV.center.y);
                       preV.center = CGPointMake(0- preV.center.x, newV.center.y);}
                   completion:^(BOOL finished){
                       [preV removeFromSuperview];
                       window.rootViewController = self.destinationViewController;
                   }];
}

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