Leak detection issue in iOS with xCode 4.3 - ios

I have a very strange issue with the xCode 4.3 memory leak instruments... Basically it does not work in the following case...
Project is created without ARC support.
Create a simple class which inherits UIView
use a "button" to create instance of this class and "leak" it... the leak will not be catch by Leak Instruments
so here is the code of the PROBLEMATIC class
#interface LeakTestView : UIView
- (id)initWithFrame:(CGRect)frame;
#end
#implementation LeakTestView
- (id)initWithFrame:(CGRect)frame
{
NSLog(#"initWithFrame called");
self = [super initWithFrame:frame];
if (self) {
// Initialization code
}
return self;
}
#end
And now I create the leak...
- (IBAction)leak:(id)sender {
LeakTestView* leak=[[LeakTestView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];
NSLog(#"class is %#", [leak class]);
}
So the problem is that this leak will not be detected...
If I change the base class to NSObject and instead of initWithFrame override init (see bellow) then the leak will be detected....
so here is the code for leak that WILL be detected
#interface LeakTestView : NSObject
- (id) init;
#end
#implementation LeakTestView
- (id) init {
NSLog(#"init called");
self = [super init];
if (self) {
}
return self;
}
#end
If I create object now and leave it - the leak detection will trigger and the leak will be "seen" into the Instruments.
- (IBAction)leak:(id)sender {
LeakTestView* leak=[[LeakTestView alloc]init];
NSLog(#"class is %#", [leak class]);
}
Any ideas what is going on? Why the leak of the UIView subclass will not be detected but changing the base class to NSObject will "fix" the issue?
Oh and yes the leaked object can be seen using the "Mark heap" - one mark before the leak and one mark after I click the button and create the leak - the class will be seen into the heap delta...
EDIT: one more "funny" situation... If I remove the "init" stuff (only alloc the object)
LeakTestView* leak=[LeakTestView alloc];
then the leak will be detected no matter what is the base class... What the hell is going on here?
EDIT2: one more "funny" thing. The Leak detection issue can be observed only in Simulator (iOS 5.0, 9A334 is mine) but the leak will be detected always if using the iPad device...
Any comments? If you dont have the issue or consider that I speek "lies" just tell me I am wrong and the above case is working "just fine" - leaks I describe are detected by your xCode instruments!

Maybe it is not leaking?
You are calling a method that is a black box. How UIView initWithFrame is implemented is none of your business. It has a contract of sorts, but you have no right to demand this to leak anymore than you can assume the retain count is 1.
Leaks is a useful tool but it doesn't do what you think it does. It does not tell you when you have messed up. It tells you when you have unreachable allocations. This is not the same thing.
Or, it might be a bug.

Related

do something before [super init] in objective-c

I would like to set a member variable in a derived object before i call [super init].
All I can find is that you should not do such a thing. My worakround, to do it anyhow, works, but actually I like to know what the consequences are when bending the rules. Or even better if there is a correct way to deal with this.
The Details:
I have several wrappers that bind a c++ object to an objective-c objec (mostly UI...View or UI...Controller)
#interface my_scrollview : UIScrollView
{
my_c_class* m_p;
}
-(id) initWithFrame:(CGRect)frame wrapper: (my_scrollview*) pWrap;
-(void) setContentOffset:(CGPoint)contentOffset;
#end
#implementation dwin_scrollview_ios
-(id) initWithFrame:(CGRect)frame wrapper: (my_scrollview*) pWrap
{
m_p = pWrap; // illegal but works?
return [super initWithFrame: frame];
//m_p = pWrap; // to late because [super init...] already called overriden func.
}
In my overwritten setContentOffset-method I need to access my C++-Object.
The Problem arises because the initWithFrame internally initializes its content using setContentOffset. So this method is called before I could "legaly" set up the link to my c++-object.
I can implement my overrides with a check if m_p is set(luckily it's initialized to nil). But I have to synchronize the state of the view and my c++-object after the the init-method. In this example this is no big deal but other such realtions are much more complicated and I end up with lot of code that repeats steps of the initialization or otherwise brings me back in sync, although before the [super init...] I know I was in sync.
Is there a pattern to solve this correct (and elegant)?
Is it really so bad to int the pointer before the call to [super init..];?
(I assume one consequence is that this crashes if [super init] returns nil...? any other cases?)
Thanks in advance
Moritz
There is nothing magical about init methods in Objective-C. alloc returns an object of the class that you want, with all instance variables initialized to 0 / nil / NULL / 0.0 etc. Each init method then just executes the code that the developer has written.
There are things that are obviously stupid, like setting an instance variable of the superclass, then calling [super init] which promptly overwrites it. And you need to be aware that init doesn't necessarily return self, but a different object, in which case everything you've initialised in the base class before calling [super init] will be gone.
// illegal but works?
No, it's not illegal. It's perfectly legitimate, although unconventional, to do stuff to an object before its superclass' initializer has been run. It may still lead to unexpected behavior and bugs, but it's not illegal per se. Sometimes it's even necessary, for example when you want to perform some computation and delegate the result of that computation to the superclass' initializer.
You are using wrong init
try this:
-(id) initWithFrame:(CGRect)frame wrapper: (my_scrollview*) pWrap
{
self = [super initWithFrame: frame];
if (self) {
m_p = pWrap;
}
return self;
}

iOS UIView inheritance bad performance

I just wanted to do performances test on iOS on my project, and I am a little bit surprised of this behaviour :
In a simple SingleView Application, if I add 1000 UITextField on rect (20, 20, 200, 200) from the viewDidLoad: main controller method, it works great. It's stupid, but it works.
Now i create my class "MyTextField" inherited from UITextField and that implements drawRect: . The drawRect: implementation does nothing and i'm not overriding any other methods of UITextField. I replace my 1000 UITextField with MyTextField class, and surprise : it crashes. Worse, my iPhone reboots !
I don't understand why. According to the Apple documentation, my drawRect does not need to call super. I also try to call super drawRect: but the result is the same. Reboot due to "Receive memory warning".
Is there an explanation to this please ?
EDIT : to be clear :
It crashed (and my iPhone reboots) :
#implementation MyTextField
-(void)drawRect:(CGRect)rect {
[super drawRect:rect];
}
#end
It crashed too (and my iPhone reboots) :
#implementation MyTextField
-(void)drawRect:(CGRect)rect {
// or does nothing
}
#end
It works :
#implementation MyTextField
#end
Here is my ViewController :
- (void)viewDidLoad {
[super viewDidLoad];
NSLog(#"######### START ###########");
for (int i = 0 ; i < 1000 ; i++) {
MyTextField *tf = [[MyTextField alloc] initWithFrame:CGRectMake(20, 20, 200, 200)];
[self.view addSubview:tf];
}
NSLog(#"######### END ###########");
}
It does nothing else
They are warning you that blank implementation of drawRect affects performance
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
I think there's no guarantee that super has an implementation of drawRect.
So calling [super drawRect:rect] might cause a crash.
The reason why it affects the performance, is because the view normally doesn't use drawRect to draw itself.
If you implement drawRect, the GPU needs to offload this part to the CPU (called offscreen rendering).
I guess you think implementing drawRect overwrites the method in a superclass.
But you should think more about the superclass checking if drawRect exists (e.g. respondsToSelector) and calling it only in this case.

App suddenly crashes while processing presentViewController method in iOS 7.1

Today, I upgrade my Xcode to the latest version(Version 5.1 (5B130a)) to support iOS 7.1.
After doing this, I run my project in Xcode as usually. Then app crashes.
I didn't change any code before upgrading the SDK version.
The code is running perfectly in iOS 5.x, 6.x, 7.0.x.
I am simply presenting another view controller in the current view controller.
they are both initialized by storyboard.
While processing presentViewController method, it gets a error message "Thread 1: EXC_BAD_ACCESS (code=2, address=0x60)". I have checked the variables, they are both alive, not a released garbage.
What's the problem with iOS 7.1??
the project is using non-ARC mechanism.
Here is my code:
#property (nonatomic, retain) ArticleViewController *articleView;
....
self.articleView = [[UIStoryboard storyboardWithName:#"MainStoryboard" bundle:nil] instantiateViewControllerWithIdentifier:#"ArticleViewController"];
...
[self presentViewController:self.articleView animated:NO completion:^() {
log(#"has shown article page...");
}];
but it works fine if presenting another view by using addSubView function:
[self.view addSubView:self.articleView.view];
I really don't know why this happens.
This happened to my app while presenting a view controller with modalPresentationStyle = UIModalPresentationCustom;
Here's how my code looks like on iOS 7.0:
//Inside my MyPresentedViewController:
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization
[self setupContent];
}
return self;
}
- (void)setupContent
{
//TransitionManager adopts UIViewControllerTransitioningDelegate and UIViewControllerAnimatedTransitioning
TransitionManager *transitionManager = [[TransitionManager alloc] init];
transitionManager.presenting = YES;
self.modalPresentationStyle = UIModalPresentationCustom;
self.transitioningDelegate = transitionManager;
}
However, the above code crashes on iOS 7.1 so I changed the implementation to:
#interface MyPresentedViewController
#property (nonatomic, strong) TransitionManager *transitionManager;
#end
...
//Inside my MyPresentedViewController:
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization
[self setupContent];
}
return self;
}
- (void)setupContent
{
//TransitionManager adopts UIViewControllerTransitioningDelegate and UIViewControllerAnimatedTransitioning
self.transitionManager = [[TransitionManager alloc] init];
_transitionManager.presenting = YES;
self.modalPresentationStyle = UIModalPresentationCustom;
self.transitioningDelegate = _transitionManager;
}
Basically, instead of declaring a transitionManager object inside the setupContent method, I created a private property (strong reference) for it.
Hm the only thing I can think of is ensuring that your articleView property is a strong reference.
#property (nonatomic, strong) ArticleViewController *articleView;
I ran into a similar issue with a picker view. In my case the pickerview was set to nil after the selection handler block, although this caused no issues as recently as last night, it was causing the app to crash this morning. Removing that line fixed the issue, however I have converted this project to ARC in the last month so you may have to find a better way to handle clean up.
This may be completely unrelated to the stated problem or answers but I ran into a similar problem when accessing an NSString on an iPhone 5S. The exact same code runs fine on an iPad and iPad at the same time.
To start out with I think it's important to state that I'm running under ARC, and I have been told repeated not to "release" any objects I instantiate in my functions. I've had problems with this before so I use some of my C# background to set almost all of my local variables to nil (null in C#). Yes, I don't trust MS GC either.
Back to the problem at hand; I have an NSString called 'data'. 'data' is read as a result from another method in a different class. Using NSLog I can see the contents of 'data'. On the next line I convert 'data' to an array to use it in scanf. That still works. On the third line I try to NSLog 'data' again, but then I get the EXC_BAD_ACCESS error. Each time it has a different address. I'm even less comfortable with ARC than I am with the Microsoft Garbage Collector so I wrapped the function in a try..catch..finally. 'data' is now sitting outside of the try..catch..finally. I'm setting 'data' to nil in the finally, which seems to fix the problem.
I know this was a bit long winded, but I would really appreciate it someone could explain why this would happen. I'm expecting to see a lot of these problems to popup all over my code now.

Where to release the shared instance in iOS

I have a shared instance (a simple data controller) and in my project I don't use ARC.
static ECOMDataController *sharedInstanse;
#implementation ECOMDataController
+(ECOMDataController *)sharedInstance
{
return sharedInstanse;
}
-(id)init
{
[self checkAndCreateDataFileIfExist];
[self readAppFile];
if (sharedInstanse)
NSLog(#"The shared instance was created already.");
sharedInstanse = self;
return self;
}
And I use it in the other methods like this:
- (void)viewDidLoad
{
[super viewDidLoad];
dataController = [ECOMDataController sharedInstance];
[dataController readAppFile];
[[self tableView] reloadData];
}
As I can see from the leaks instrument - I have a memory leak here - what should I do to release the data controller? And where is better to do that?
Rocky is right: you wouldn't deallocate a singleton. Frankly, I wouldn't use that pattern at all--except for system calls like AppDelegate or NSNotificationCenter. There are a lot of pitfalls with the pattern...but that's my opinion (though I'm not alone in it).
More importantly, why are you not using ARC? There's absolutely no reason not to, and many reasons for it. Especially for a newer developer, there's no sense in fussing about memory management when the compiler will do it for you, anyway--and will do a better job of it. You have enough to learn without fussing over retain counts!

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;
And 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.

Resources