Question

I have a few, full screen, UIColor PatternImages (in scrollViews) in my iPad app and am experiencing some memory problems (surprise?)
When I started having memory issues, I implemented lazy loading in my scrollviews.
When the problems continued, I moved away from factory methods
(like [UIColor colorWithPatternImage:...])
to “alloc”ed methods
(like [[UIColor alloc]initWithPatternImage:...]),
so I could respond to memory warnings by releasing pages.

However, whenever I release my UIColor PatternImages, I get an “EXC_BAD_ACCESS” error.

At first I thought this might be caused by my [UIImage imageNamed:...] pattern images, so I switched to [[UIImage alloc]initWithContentsOfFile:...] images, but this didn’t help. Just now I set NSZombiesEnabled and it tells me that the problem is:

-[UICGColor release]: message sent to deallocated instance 0x187b50

With the backtrace:

#0  0x35823910 in ___forwarding___ ()
#1  0x35823860 in __forwarding_prep_0___ ()
#2  0x357e53c8 in CFRelease ()
#3  0x357e48de in _CFAutoreleasePoolPop ()
#4  0x3116532c in NSPopAutoreleasePool ()
#5  0x341a7508 in _wrapRunLoopWithAutoreleasePoolHandler ()
#6  0x3580ac58 in __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ ()
#7  0x3580aacc in __CFRunLoopDoObservers ()
#8  0x358020ca in __CFRunLoopRun ()
#9  0x35801c86 in CFRunLoopRunSpecific ()
#10 0x35801b8e in CFRunLoopRunInMode ()
#11 0x320c84aa in GSEventRunModal ()
#12 0x320c8556 in GSEventRun ()
#13 0x341dc328 in -[UIApplication _run] ()
#14 0x341d9e92 in UIApplicationMain ()
#15 0x00002e5e in main (argc=1, argv=0x2fdff610) at...

I don’t have any UICGColor objects either, so I’m thinking that somehow my “alloc”ed UIColors have underlying UICGColor autorelease objects…? Any ideas/insight?

Answer 1

OK, I have worked something out, thanks in part to the (poorly tagged and titled) SO question/answers here. What I needed to do was read-up about UIView.backgroundColor. In my docs it says @property(nonatomic, copy) UIColor *backgroundColor. The “copy” here tells me that when I say something like:

myUIView.backgroundColor=[[UIColor alloc]initWithPatternImage:myUIImage];

The myUIView.backgroundColor is actually a different object to the [[UIColor alloc]initWithPatternImage:myUIImage]. This separate myUIView.backgroundColor is, in fact, autoreleased, so when I go [myUIView.backgroundColor release]; I am actually shooting myself in the foot. What I need to do is:

UIColor* tmpColor=[[UIColor alloc]initWithPatternImage:myUIImage];
currentPage.backgroundColor=tmpColor;
[tmpColor release];

(and of course, around that, I’m also allocing and releasing myUIImage). Now to release my scrollView patternImage, I can just do something like currentPage.backgroundColor=nil; (like @BuildSucceeded) or currentPage.backgroundColor=[UIColor clearColor]; (not sure if there is a practical difference). I guess internally, both of these cause currentPage to autorelease the old backgroundColor. Since making these changes, I haven’t been able to get my app to crash.

I need to say this: I don’t think C++ does it quite right, but C# and Java both manage quite nicely without any of this complicated release, autorelease, @property business. Of course, if someone wanted to implement an analogous (to Objective-C) pointer management system in Java or C# they could, but of course no one wants this because it would be pretty useless. Pleeeease Apple, migrate away from Objective-C!