UIImage deallocate problem

Question

Hi,

i've been pulling my hair over this problem, i've read all the post about deallocation problem but couldnt understand why, because i'm pretty new with objective-c and iphone, as you can tell :)

but what i dont understand is this block of code below saying i've over-deallocated UIImage, now i have tried everything but the app still crashes

UIImage *imageSave      = [UIImage imageNamed:@"btn_save.png"];
UIButton *btnSave       = [UIButton buttonWithType:UIButtonTypeCustom];

[btnSave setBackgroundImage:imageSave forState:UIControlStateNormal];

btnSave.frame = CGRectMake(0, 0, imageSave.size.width, imageSave.size.height);

[btnSave addTarget:self action:@selector(save) forControlEvents:UIControlEventTouchUpInside];

UIBarButtonItem *barBtnSave = [[UIBarButtonItem alloc] initWithCustomView:btnSave];

self.navigationItem.rightBarButtonItem  = barBtnSave;

//[imageSave release];
//[btnSave release];
[barBtnSave release];


UIImage *imageCancel    = [UIImage imageNamed:@"btn_cancel.png"];
UIButton *btnCancel     = [UIButton buttonWithType:UIButtonTypeCustom];

[btnCancel setBackgroundImage:imageCancel forState:UIControlStateNormal];

btnCancel.frame = CGRectMake(0, 0, imageCancel.size.width, imageCancel.size.height);

[btnCancel addTarget:self action:@selector(cancel) forControlEvents:UIControlEventTouchUpInside];
UIBarButtonItem *barBtnCancel = [[UIBarButtonItem alloc] initWithCustomView:btnCancel];

self.navigationItem.leftBarButtonItem   = barBtnCancel;

//[imageCancel release];
//[btnCancel release];
[barBtnCancel release];

Answer 1

Ok, let's take a look at these 2 lines:

UIImage *imageCancel = [UIImage imageNamed:@"btn_cancel.png"];

[imageCancel release];

In 1 line, you create an autorelease image, then the retainCount would be 0. Then, you release the image, which would make the retainCount is -1, causing the crash

What you need to remember is a list of increasing your retainCount: alloc, copy, retain ... If you call one of these methods to an object, you have to do either : autorelease or release