为什么我的视图控制器（从故事板 segue 模态显示）在被解雇后没有被释放？答案

【问题标题】：Why does my view controller (presented modally from a storyboard segue) not get released after being dismissed?为什么我的视图控制器（从故事板 segue 模态显示）在被解雇后没有被释放？
【发布时间】：2013-08-17 05:41:19
【问题描述】：

我的视图控制器（下面的代码）是从故事板 segue（附加到 UIButton）模态呈现的。一旦点击（动态生成的）按钮之一，它就会被关闭。由于某种原因，它随后没有被释放（保留计数为 1）。

显然，首先要关注的是两个对象（PPAPI 和 PPObjectCache），它们将此对象作为委托（在 viewDidLoad 中注册），但是它们都使用弱引用，如果我能得到其他任何东西，ARC 将自动将其设为 NULL保留它以释放它。我已经验证这些对象没有对该视图控制器进行强引用。

我已使用 Instruments（分配配置文件）检查此对象的保留/释放，报告显示在代码下方。如您所见，不平衡出现在 UIKit 或 Foundation 代码中，但我很难确切地知道在哪里，或者为什么。

谁能发现 UIKit 或 Foundation 坚持使用我的视图控制器的原因？

#import "PPLoginViewController.h"
#import "PPAppDelegate.h"

@interface PPLoginViewController () {
    NSArray *employeeIDs;
}

@end

@implementation PPLoginViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    PPAPI *api = [PPAPI api];
    [api subscribeToViewsOfType:@"employees" delegate:self];
    [[PPObjectCache cache] subscribeToChangesToObjectsOfType:@"worker" delegate:self];
    [api callMethod:@"main.tasks.get_employees" withParameters:@{} callback:nil];
}

// PPAPI view subscription delegate method
- (void)receivedObjectIDs:(NSArray *)objectIDs forViewType:(NSString *)viewType {
    NSLog(@"%@: GOT VIEW", self);
    dispatch_async(dispatch_get_main_queue(), ^{
        employeeIDs = objectIDs;
        [self reload];
    });
}

// PPObjectCache delegate method
- (void)objectChanged:(id)object {
    dispatch_async(dispatch_get_main_queue(), ^{
        [self reload];
    });
}

- (void)reload {
    [[self.view.subviews filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {
        return [evaluatedObject isKindOfClass:[UIButton class]];
    }]] makeObjectsPerformSelector:@selector(removeFromSuperview)];

    UIDevice *currentDevice = [UIDevice currentDevice];
    CGFloat y = 75.f;
    for (NSNumber *employeeID in employeeIDs) {
        NSDictionary *employee = [[PPObjectCache cache] objectOfType:@"worker" withID:employeeID];

        UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        [button setTitle:employee[@"name"] forState:UIControlStateNormal];
        button.titleLabel.font = [UIFont boldSystemFontOfSize:18.f];
        button.tag = [employeeID integerValue];
        button.frame = CGRectMake((self.view.bounds.size.width - 240.f) / 2.f, y, 240.f, currentDevice.userInterfaceIdiom == UIUserInterfaceIdiomPad ? 60.f : 45.f);
        [button addTarget:self action:@selector(login:) forControlEvents:UIControlEventTouchUpInside];
        [self.view addSubview:button];

        y += currentDevice.userInterfaceIdiom == UIUserInterfaceIdiomPad ? 75.f : 65.f;
    }
}

// UIButton action from above
- (void)login:(UIButton *)sender {
    PPAppDelegate *delegate = (PPAppDelegate *)[UIApplication sharedApplication].delegate;
    delegate.loggedInEmployee = [[PPObjectCache cache] objectOfType:@"worker" withID:@(sender.tag)];
    // self.logoutButton is an @property (weak) set from the presenting view controller
    self.logoutButton.title = [NSString stringWithFormat:@"Logout %@", delegate.loggedInEmployee[@"initials"]];

    [self dismissViewControllerAnimated:YES completion:nil];
}

@end

分配报告如下（抱歉格式不正确）。如您所见，我的应用程序代码负责的事件都是平衡的（显示为保留/释放组或紧随其后的是平衡调用）。 UIKit 或 Foundation 中的某些东西没有释放我的视图控制器！

#   Event Type  ∆ RefCt RefCt   Timestamp   Responsible Library Responsible Caller
0   Malloc  +1  1   00:19.062.502   UIKit   -[UIClassSwapper initWithCoder:]
1   Retain  +1  2   00:19.062.991   UIKit   -[UIRuntimeConnection initWithCoder:]
2   Retain  +1  3   00:19.063.036   UIKit   -[UIRuntimeConnection initWithCoder:]
3   Retain  +1  4   00:19.063.230   UIKit   UINibDecoderDecodeObjectForValue
4   Retain  +1  5   00:19.063.274   UIKit   UINibDecoderDecodeObjectForValue
5   Retain  +1  6   00:19.063.315   Foundation  -[NSObject(NSKeyValueCoding) setValue:forKey:]
6   Retain  +1  7   00:19.063.388   UIKit   -[UINib instantiateWithOwner:options:]
    Release (2) -2      00:19.063.568   UIKit   -[UINibDecoder finishDecoding]
8   Release -1  5   00:19.063.599   UIKit   -[UINibDecoder finishDecoding]
10  Release -1  3   00:19.063.722   UIKit   -[UIRuntimeConnection dealloc]
11  Release -1  2   00:19.063.755   UIKit   -[UIRuntimeConnection dealloc]
12  Retain  +1  3   00:19.063.920   UIKit   -[UIStoryboardSegue initWithIdentifier:source:destination:]
    Retain/Release (2)          00:19.067.387   Purchase    -[PPMasterViewController prepareForSegue:sender:]
15  Retain  +1  4   00:19.072.460   UIKit   -[UIViewController setChildModalViewController:]
16  Retain  +1  5   00:19.076.305   UIKit   -[UINib instantiateWithOwner:options:]
17  Retain  +1  6   00:19.076.366   UIKit   -[UINib instantiateWithOwner:options:]
18  Retain  +1  7   00:19.076.582   UIKit   -[UIProxyObject initWithCoder:]
19  Retain  +1  8   00:19.076.587   UIKit   -[UIRuntimeConnection initWithCoder:]
20  Retain  +1  9   00:19.080.167   UIKit   UINibDecoderDecodeObjectForValue
21  Retain  +1  10  00:19.080.230   UIKit   UINibDecoderDecodeObjectForValue
22  Release -1  9   00:19.080.449   UIKit   -[UINib instantiateWithOwner:options:]
23  Release -1  8   00:19.080.507   UIKit   -[UINib instantiateWithOwner:options:]
24  Release -1  7   00:19.080.578   UIKit   -[UINibDecoder finishDecoding]
    Release (2) -2      00:19.080.602   UIKit   -[UINibDecoder finishDecoding]
26  Release -1  5   00:19.080.716   UIKit   -[UIRuntimeConnection dealloc]
    Retain/Release (2)          00:19.081.788   Purchase    -[PPAPI subscribeToViewsOfType:delegate:]
    Retain/Release (2)          00:19.081.866   Purchase    -[PPObjectCache subscribeToChangesToObjectsOfType:delegate:]
32  Retain  +1  5   00:19.089.975   UIKit   -[UIWindow _setRotatableClient:toOrientation:updateStatusBar:duration:force:isRotating:]
33  Retain  +1  6   00:19.091.352   UIKit   __91-[UIWindowController transition:fromViewController:toViewController:target:didEndSelector:]_block_invoke_0238
    Retain/Release (2)          00:19.105.379   UIKit   -[UIResponder becomeFirstResponder]
36  Retain  +1  7   00:19.106.122   UIKit   -[UIViewController presentViewController:withTransition:completion:]
37  Retain  +1  8   00:19.106.142   UIKit   -[UIViewController presentViewController:withTransition:completion:]
38  Release -1  7   00:19.108.717   UIKit   _UIApplicationHandleEvent
39  Release -1  6   00:19.109.517   UIKit   -[UIStoryboardSegue dealloc]
40  Release -1  5   00:19.109.534   UIKit   _UIApplicationHandleEvent
41  Release -1  4   00:19.109.581   UIKit   -[UIStoryboardScene dealloc]
    Retain/Autorelease/Release (5)  +1      00:19.145.293   Foundation  -[NSConcreteHashTable countByEnumeratingWithState:objects:count:]
    Retain (2)  +2      00:19.151.847   Purchase    -[PPLoginViewController receivedObjectIDs:forViewType:]
    Retain (2)  +2      00:19.151.874   Purchase    __copy_helper_block_
    Release (2) -2      00:19.151.888   Purchase    -[PPLoginViewController receivedObjectIDs:forViewType:]
    Release (2) -2      00:19.278.813   Purchase    __destroy_helper_block_
48  Release -1  4   00:19.541.189   UIKit   -[UIWindowController transitionViewDidComplete:fromView:toView:removeFromView:]
    Retain/Release (2)          00:19.996.260   UIKit   -[UIViewController _dismissViewControllerWithTransition:from:completion:]
51  Release -1  3   00:19.996.269   UIKit   -[UIViewController _dismissViewControllerWithTransition:from:completion:]
52  Release -1  2   00:19.996.302   UIKit   -[UIPeripheralHost(UIKitInternal) _stopPinningInputViewsOnBehalfOfResponder:]
53  Retain  +1  3   00:19.996.776   UIKit   -[UIViewController _dismissViewControllerWithTransition:from:completion:]
54  Retain  +1  4   00:20.001.379   UIKit   __91-[UIWindowController transition:fromViewController:toViewController:target:didEndSelector:]_block_invoke_0238
55  Release -1  3   00:20.002.196   UIKit   -[UIViewController _dismissViewControllerWithTransition:from:completion:]
56  Retain  +1  4   00:20.432.653   UIKit   -[UIViewController _didFinishDismissTransition]
57  Release -1  3   00:20.432.658   UIKit   -[UIViewController setChildModalViewController:]
58  Release -1  2   00:20.432.662   UIKit   -[UIViewController _didFinishDismissTransition]
59  Release -1  1   00:20.432.706   UIKit   -[UIWindowController transitionViewDidComplete:fromView:toView:removeFromView:]
    Retain/Autorelease (2)  +1      00:20.663.794   Foundation  hashProbe

【问题讨论】：

尝试在你的块中使用 __block 对 self 的引用。 __block PPLoginViewController *bself = self;
没有改变在每个块之前添加上面的代码行并将块更改为引用bself而不是self。谢谢你的主意。我认为，如果类似的事情导致了不平衡的保留（我看不出有什么办法），它会显示在上面的分配报告中。显示了块保留，但通过发布来平衡。
是的，dealloc 没有被调用，因为 Foundation 或 UIKit 中的某些东西保留了我的视图控制器（如分配报告所示）。我尝试从代码中删除所有块（改用[self performSelectorOnMainThread:@selector(reload) withObject:nil waitUntilDone:NO]），但问题仍然存在。在仍然使用积木的同时添加弱自我/强自我舞蹈没有区别。无论如何都没有存储块（GCD 执行然后释放它们），因此将 self 保留在块中不会导致循环。见stackoverflow.com/questions/7565953

标签： ios objective-c automatic-ref-counting

【解决方案1】：

正如我所料，这是我自己的愚蠢错误，但我会在这里回答，以防它对任何人有用！

PPAPI 为视图订阅维护一个带有弱引用的NSHashTable，如果订阅的对象被释放，它将被 ARC 自动归零。似乎从NSHashTable 获取对象时，它们被保留，然后由 Foundation 自动释放。

PPAPI 在后台 GCD 队列上的 while(1) 循环内访问 NSHashTable（这可能是糟糕的设计）。因为while(1) 循环使队列保持忙碌，所以自动释放池从未耗尽，结果PPLoginViewController 被Foundation 保留并且从未释放。

一种解决方法是将while(1) 循环的内容放在@autoreleasepool { } 块中。

这方面的线索是分配报告的最后一行，显示的是Retain/Autorelease，而不是Retain/Autorelease/Release。

【讨论】：