内存警告已释放视图控制器？

Question

我有一个主 UIViewcontroller (vcMain)，其中有两个 UIViewControllers 是主控制器的子类。两个子类 UIViewcontrollers (vcSub1/vcSub2) 仅显示图像和更多控件。 vcSub1 和 vcSub2 显示在 UITabBarController 中。 我已经实现了 didReceiveMemoryWarning 如下：

vcMain:

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning]; 

    if ([self isViewLoaded] == NO) {
        // release the model, will be recreated in viewDidLoad
        [_brain release], self.brain = nil; 
    }
}

vcSub1:

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];    

    if ([self isViewLoaded] == NO) {
        // will be recreated in viewDidLoad, only exists in vcSub1
        [self.zoomBrain release], [self setZoomBrain:nil];

        _button = nil; // autoreleased, created programmatically
    }
}

vcSub2:

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning]; 

    if ([self isViewLoaded] == NO) {
        // nothing in here (yet)
    }
}

当我第一次模拟内存警告时一切似乎都工作正常。

Received simulated memory warning.
-[AppDelegate applicationDidReceiveMemoryWarning:] [Line 81] 
-[vcSub2 didReceiveMemoryWarning] [Line 102] 
-[vcMain didReceiveMemoryWarning] [Line 73] 
-[vcSub2 viewDidUnload] [Line 112] 
-[vcMain viewDidUnload] [Line 65] 
-[vcSub1 didReceiveMemoryWarning] [Line 150] 
-[vcMain didReceiveMemoryWarning] [Line 73] 
-[vcSub1 viewDidUnload] [Line 143] 
-[vcMain viewDidUnload] [Line 65] 

我可以一次又一次地这样做，没有任何问题。但是，如果我切换选项卡（从而重新加载视图）并再次模拟内存警告，我会得到以下信息：

Received simulated memory warning.
-[AppDelegate applicationDidReceiveMemoryWarning:] [Line 81] 
-[vcSub2 didReceiveMemoryWarning] [Line 102] 
-[vcMain didReceiveMemoryWarning] [Line 73] 
-[vcSub1 didReceiveMemoryWarning] [Line 150] 
-[vcMain didReceiveMemoryWarning] [Line 73] 
-[vcSub1 viewDidUnload] [Line 143] 
-[vcMain viewDidUnload] [Line 65] 
*** -[vcSub1 isViewLoaded]: message sent to deallocated instance 0x614de80

info malloc-history 0x614de80 显示该实例是 vcSub1视图控制器。

Alloc: Block address: 0x0614de80 length: 192
Stack - pthread: 0xa0425540 number of frames: 21
    0: 0x93f7f0a3 in malloc_zone_calloc
    1: 0x93f7effa in calloc
    2: 0x154a2d4 in class_createInstance
    3: 0x13165d8 in +[NSObject(NSObject) allocWithZone:]
    4: 0x13163da in +[NSObject(NSObject) alloc]
    5: 0x2bf0 in -[AppDelegate application:didFinishLaunchingWithOptions:] at AppDelegate.m:47
    6: 0x8dec89 in -[UIApplication _callInitializationDelegatesForURL:payload:suspended:]
    7: 0x8e0d88 in -[UIApplication  _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:]
    8: 0x8eb617 in -[UIApplication handleEvent:withNewEvent:]
    9: 0x8e3abf in -[UIApplication sendEvent:]
   10: 0x8e8f2e in _UIApplicationHandleEvent
   11: 0x30b9992 in PurpleEventCallback
   12: 0x13d3944 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__
   13: 0x1333cf7 in __CFRunLoopDoSource1
   14: 0x1330f83 in __CFRunLoopRun
   15: 0x1330840 in CFRunLoopRunSpecific
   16: 0x1330761 in CFRunLoopRunInMode
   17: 0x8e07d2 in -[UIApplication _run]
   18: 0x8ecc93 in UIApplicationMain
   19: 0x28f9 in main at main.m:14
   20: 0x2875 in start

为什么以及如何释放我的 vcSub1 视图控制器？

Answer 1

我认为您释放对象的次数太多了。假设您的属性是（保留），那么您这里有一个错误：

[self.zoomBrain release]
[self setZoomBrain:nil];

第一行将释放 ZoomBrain。

第二行将释放zoomBrain，然后将其设置为nil。

您将发布两次 - 您只需要第二行。如果你使用setter方法（即setZoomBrain:）那么它会自动为你释放之前的zoomBrain。

这也是同样的情况：

[_brain release];
self.brain = nil; 

对 self.brain 的调用是一种不同的编写方式 [self setBrain:nil]; - 同样，release 将被调用两次。

在每种情况下您只需要第二行：

self.brain = nil;