- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];

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

- (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
    }
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];

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

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]

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

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

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

[_brain release];
self.brain = nil;

self.brain = nil;