Why does Instruments think this is leaking memory? - objective-c

Question

I have an About View which I push onto a NavigationController. The view has one UILabel which is connected to an IBOutlet. In viewDidLoad I populate the UILabel with the bundle version number (a string). Testing with instruments suggested that the line marked with a comment is leaking memory: -
viewDidLoad {
[super viewDidLoad];
self.title = #"About";
// Line below is the suggested culprit ***
NSString *versionLabel = [[NSString alloc] initWithFormat:#"Version %#",
[[[NSBundle mainBundle] infoDictionary] objectForKey:(NSString *)kCFBundleVersionKey]];
self.applicationVersion.text = versionLabel;
[versionLabel release];
versionLabel = nil;
}
I'm assuming it is suggesting the NSString and not anything else on the line ...
My questions is Why ?

Answer 1

My suspicion is that you're leaking the applicationVersion UILabel. That will cause the string to leak as a by-product. The most common reason for this on iPhone is failure to follow the NIB memory management rules.

Answer 2

It may actually be the mainBundle or infoDictionary that is leaking - it is possible that the system is caching one or other of those and thus they are being created and then never released.
Try adding in to your applicationDidFinishLaunching the code:
[[NSBundle mainBundle] infoDictionary];
Without any other code and see if Leaks points to that line as the location of the leak. In that case, caching is the issue and you can ignore it.

Answer 3

You don't even need to create an instance of NSString in that case, simply use the following method that acts on the NSString class (not an instance):
NSString *versionLabel = [NSString stringWithFormat:#"Version %#",
[[[NSBundle mainBundle] infoDictionary]
objectForKey:(NSString*)kCFBundleVersionKey]];
If you use NSString this way, you do not have to release versionLabel because memory was never allocated.