一个模拟推送Segue的自定义Segue将VC变成Zombie

Question

[使事情简短明了]

我写了一个自定义的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]; }];
}

触发segue时没有异常.但是它会解除分配 destinationViewController.

当点击一个触发另一个segue的按钮时,应用程序会崩溃destinationViewController.

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

[细节]

我最近开始使用Object-C,我编写了一个模拟push segue的自定义segue.

它第一次被触发,一切正常.

但在那之后,无论触发什么segue,应用程序崩溃,我都会收到EXC_BAD_ACCESS错误.

---

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.

我的第二个猜测是,这与由UIView和提供的基础设施有关UIWindow.但是,由于我缺乏知识和经验,我再也无法弄清楚真正的问题是什么.

我知道我实际上可以采用一种简单的方法,通过使用a rootviewcontroller并简单地隐藏导航栏来创建push segue ,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,并了解下面发生了什么.代码结构.

---

[更新]

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

这是我意识到的:

1. 在按钮触发自定义segue之后,只有当按钮触发下一个segue时,app才会崩溃.使用触发下一个segue viewDidAppear不会导致任何崩溃.

2. 坠机背后的主要原因:

Objective-C消息被发送到解除分配的对象(僵尸)

[#,事件类型,refCt,图书馆,来电者]

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(如果我没错)

自定义segue以某种方式触发了释放对象的内容,在destinationViewController触发另一个segue的按钮(in )之后将向其发送Objective-C消息.

---

更多细节

没有一个prepareForSegue被调用,因为我不需要在视图之间传递数据.

我的segues都以同样的方式触发:

- (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,所以我自己并没有真正进行任何释放.

---

[更新2]

已经变成僵尸的对象是destinationViewController自定义segue的对象.

不调用removeFromSuperview自定义segue不会阻止对象变成僵尸.

只要我使用常规模型segue或push segue(使用rootViewController)而不是我制作的自定义模型,就不会有任何僵尸,一切都会正常工作.

Answer 1

你的崩溃只是因为你的新控制器在segue执行后没有保留.

你做的是这样的:

• src和dest控制器被实例化
• 你执行你的动画
• 在完成中删除src视图
• 你的src控制器被释放,但是窗口rootViewController 仍然指向它,你的目标视图控制器没有被添加到窗口的层次结构中.

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;
                   }];
}