Objective-C memory management issues

I am new to iPhone programming and Objective-C. I am building a View-based application.

The problem is that none of the UIViewController's dealloc functions are ever called. I have decided to unload all my retained objects programmaticaly, right before presenting the next UIViewController class. I have resolved all the leaks detected by Xcode, tested the application with Leaks and Allocations Tools and everything seams OK, but the memory used builds up to around 180 MB and the app crashes.

The self.retainCount before presenting the next UIViewController is 1, the objects owned are released and the pointers are nil, but still the memory builds up.

Can you give me a clue? If needed I will post some code samples. Or can you send me some references to something like Objective-C memory management 101?

This is my interface:

@interface GameScreen : UIViewController
{
    IBOutlet UILabel     *timeLabel;
    IBOutlet UIView      *gameView;
    IBOutlet UIImageView *gameViewFrame;
    IBOutlet UIButton    *showOutlineButton;    
    UIImage *puzzleImage;
    UIView *optionsView;
    UIView *blockView;  
    NSTimer *timer;
    UIImageView *viewOriginalPicture;
    SHKActivityIndicator *activityIndicator;
    BOOL originalPictureShown;
    BOOL outLineShown;
}

@property (nonatomic, retain) IBOutlet UILabel     *timeLabel;
@property (nonatomic, retain) IBOutlet UIView      *gameView;
@property (nonatomic, retain) IBOutlet UIImageView *gameViewFrame;
@property (nonatomic, retain) IBOutlet UIButton    *showOutlineButton;
@property (nonatomic, retain) UIImage *puzzleImage;

开发者_如何学PythonAnd here is the implementation:

- (id) initWithPuzzleImage: (UIImage *) img
{
if((self = [super init]))
{
    puzzleImage = [[UIImage alloc] init];
    puzzleImage = img;
}
return self;
}

This is the function called when the user taps the exit button:

- (void) onExit
{   
[timer invalidate];
CurrentMinuts = 0;
CurrentSeconds = 0;

    //remove piece configurations
    [pieceConfigMatrix removeAllObjects];
    [pieceFramesMatrix removeAllObjects];

PuzzleViewController *modalView = [[PuzzleViewController alloc] init];
    [self unloadObjects];
[self presentModalViewController:modalView animated:YES];
[modalView release];

}

And the unloadObjects function:

- (void) unloadObjects
{
    [self resignFirstResponder];         
    [viewOriginalPicture release];
    viewOriginalPicture = nil;  
    [timeLabel release];
    timeLabel = nil;
    [gameView release];
    gameView = nil;
    [originalImage release];
    originalImage = nil;
    [gameViewFrame release];
    gameViewFrame = nil;
    [timer release];
    [showOutlineButton release];
    showOutlineButton = nil;    
}

I have a lead of what I do wrong, but I am not sure. Let me explain. I am adding the puzzle pieces to the 'gameView' property. For this, I have a 'SplitImage' object. The following function is called in - (void) viewDidLoad:

- (void) generatePuzzleWithImage:(UIImage *) image
{   
    SplitImage *splitSystem = [[SplitImage alloc] initWithImage:image andPuzzleSize:gPuzzleSize];
    [splitSystem splitImageAndAddToView:self.gameView];
    [splitSystem release];
}

Next, initialization function for the SplitImage class and the splitImageAndAddToView function:

- (id) initWithImage: (UIImage *) image andPuzzleSize: (int) pSize
{
    if((self = [super init]))
    {
        UIImage *aux = [[[UIImage alloc] init] autorelease];
        pieceCenterSize = [SplitImage puzzlePieceSizeForNumberOfPieces:pSize];

        UIImage *outSideBallSample = [UIImage imageNamed:@"sampleHorizontal.jpg"]; //convexity size for puzzle size
        outSideBallSample = [outSideBallSample resizedImageWithContentMode:UIViewContentModeScaleAspectFit bounds:CGSizeMake(pieceCenterSize, pieceCenterSize) interpolationQuality:kCGInterpolationHigh];      
    outSideBallSize = roundf(outSideBallSample.size.height);

        puzzleSize = pieceCenterSize * pSize;

        pieceNumber = pSize;

        if(image.size.height < puzzleSize || image.size.height > puzzleSize || image.size.width < puzzleSize || image.size.width > puzzleSize)
    {
        aux = [SplitImage resizeImageForPuzzle:image withSize:puzzleSize];
        aux = [SplitImage cropImageForPuzzle:aux withSize:puzzleSize];
    }

    aux = [aux imageWithAlpha];
    originalImage = [[UIImage imageWithCGImage:aux.CGImage] retain];

    mainImage = aux.CGImage;
    imageSize = CGSizeMake(aux.size.width, aux.size.height);
    NSLog(@"%@", NSStringFromCGSize(imageSize));

    splitImageSize = CGSizeMake(pieceCenterSize + 2*outSideBallSize, pieceCenterSize+2*outSideBallSize);
    }   
return self;
}



- (void) splitImageAndAddToView: (UIView *) view
{   
    for (int i = 0; i < pieceNumber; i++)
    for(int j = 0; j < pieceNumber; j++)

    //some code

    UIImage *mask;
    mask = [self randomlyRetriveMaskWithPrefix:1 forPieceAtI:i andJ:j];
    CGImageRef split = CGImageCreateWithImageInRect(mainImage, cuttingRect);

    PuzzlePiece *splitView = [[PuzzlePiece alloc] initWithImage:[UIImage imageWithCGImage:split] andMask:mask centerSize:pieceCenterSize objectMatrixPosition:i*pieceNumber+j outSideBallSize:outSideBallSize pieceType:pieceType pieceFrame:cuttingRect];

    [pieceFramesMatrix addObject:[NSValue valueWithCGRect:cuttingRect]];
    [splitView setTag:(i+1)*100+j];
    [view addSubview:splitView];
    CGImageRelease(split);
    [splitView release];
    }

Thank you, Andrei

---

Objective-C memory management 101 is here:

https://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/MemoryMgmt/MemoryMgmt.html

Ignore the stuff on garbage collection, it isn't available for iOS.

---

It's not normal to release objects before presenting the next UIViewController.

Assuming you have a NIB, its contents will be loaded the first time that you (or the system) accesses the view member. Your view controller will get a call to loadView, then subsequently to viewDidLoad. If you have any views you want to add programmatically, you can do that in loadView or viewDidLoad, if you want to interrogate objects loaded from the NIB then you can do that in viewDidLoad.

Once loaded, the view will remain in memory unless and until a low memory warning occurs. At that point it'll be released. You'll get viewDidUnload. You should release anything view related that you've still got an owning reference to in there, and set to nil any weak references you may have.

Any attempt to access the view property subsequently will cause the NIB to be reloaded, etc.

So, when presenting a new UIViewController, just present it. If you create objects that are used only for display of that controller then do so on viewDidLoad, and release them on viewDidUnload.

That all being said, the Leaks tool in Instruments should be able to tell you which types of object are leaking and where you first allocated them, so it makes finding leaks really quite easy. The only thing to watch out for is that if one object handles its properties/members entirely correctly but is itself leaked then anything it creates will generally also leak. So when something leaks, check the thing that created it isn't also leaking before tearing your hair out over why you can't find a problem.

---

First, retainCount is useless.

Activity Monitor is pretty close to just as useless. As well, the behavior in the simulator can be quite different on the memory use front. Better to focus debugging of a problem like this on the device.

Next, this:

The problem is that none of the UIViewController's dealloc functions are ever called. I have decided to unload all my retained objects programmaticaly, right before presenting the next UIViewController class.

Any time you find yourself programmatically working around incorrect behavior, you are just creating more bugs.

Step back from your custom hack and figure out why the dealloc isn't being called. Something somewhere is over-retaining the object. The allocations instrument with retain tracking turned on will show you exactly where all retains and releases are sent to the errant objects.

Leaks likely won't show anything if whatever is retaining the objects is still reachable from a global or the stack (i.e. leaks are objects that can never be used by your program again -- but there are many more ways to explode memory use without it being truly a leak).

You should also "Build and Analyze", then fix any problems it identifies.

Next, if you are seeing memory accretion of repeated operations on the user's part, then Heapshot analysis is extremely effective at figure out exactly what has gone wrong.

Some specific comments:

puzzleImage = [[UIImage alloc] init];
puzzleImage = img;

2 bugs; you are leaking a UIImage and not retaining img. That your app doesn't crash in light of the above code indicates that there is likely an over-retain elsewhere.

---

retainCount is not a reliable debugging tool.

You should never pay attention to or rely on retainCount. Just because you released it does not mean that some part of the program does not still have a reference to it. retainCount has no value.

Generally as a rule of thumb. If you use 'alloc' you must 'release' at some point.

Unless ofcourse you have put it into an autorelease pool.

Leaks should be able to point you to the objects that are leaking, using that, narrow down to where those objects are added, stored etc.

Post examples of your code on how you instantiate objects and where you release them, you maybe doing something wrong early on.

edit: apologies, i put 'init' not 'alloc' previously, thank you dreamlax, early morning mistake.