Question

I have used some code from Apple’s ‘Camera Programming Topics for iOS’ guide as follows:

UIImagePickerController *cameraUI = [[UIImagePickerController alloc] init];
cameraUI.sourceType = UIImagePickerControllerSourceTypeCamera;

// Displays a control that allows the user to only take picture:
cameraUI.mediaTypes = [[NSArray alloc] initWithObjects: (NSString *) kUTTypeImage, nil];

// Hides the controls for moving & scaling pictures, or for trimming movies. To instead show the controls, use YES.
cameraUI.allowsEditing = NO;

cameraUI.delegate = delegate;

[controller presentModalViewController: cameraUI animated: YES];
[cameraUI release];

However, when I ‘Analyze’ my code, Xcode says I have a potential leak from the following line:

cameraUI.mediaTypes = [[NSArray alloc] initWithObjects: (NSString *) kUTTypeImage, nil];

I have no other release commands than those shown above. Given the array in question is an attribute of cameraUI (which is released), Im not sure what I should do (if anything).

Any thoughts?

Answer 1

Unless cameraUI.mediaTypes property is defined with assign, there is indeed a leak here. It may help to break up the line into multiple steps, just for instruction.

NSArray* mediaTypes = [[NSArray alloc] initWithObjects: (NSString *) kUTTypeImage, nil];
cameraUI.mediaTypes = mediaTypes;

If cameraUI takes care of its own memory, it shouldn’t matter what you assign or when. But, in that first line, you’re constructing a variable but never releasing it. So, how do you fix this? The standard way to fix it is by autoreleasing during construction.

cameraUI.mediaTypes = [[[NSArray alloc] initWithObjects: (NSString *) kUTTypeImage, nil] autorelease];

If you’re working with very large objects that must be released as soon as possible, you’ll need to manually release it once it’s been passed to cameraUI:

NSArray* mediaTypes = [[NSArray alloc] initWithObjects: (NSString *) kUTTypeImage, nil];
cameraUI.mediaTypes = mediaTypes;
[mediaTypes release];

Only use the second form if you need it – it’s much more prone to error.