Question

Is it necessary to set all @propertys with retain modifier declared as IBOutlet to nil inside the - (void)dealloc method? Will memory be consumed / wasted if I don’t do so?

Assume that Automatic Reference Counting is turned OFF.

Answer 1

Your question seems to be “How do I handle a retain property in dealloc?” Well let’s look at an example.

@property (retain, nonatomic) IBOutlet UIView *myView;

When your view is loaded myView is retained by two objects, your view hierarchy (by an internal addSubview: or similar) and your view controller (by means of the property setter method). A simple log is all that is needed to confirm this. placing this code in viewDidLoad will confirm this with an output of 2.

NSLog(@"myLabel is retained: %i", myView.retainCount);

There are two methods where you should address this pointer, and both are automatically filled in for you by Xcode.

First in viewDidUnload (Which is generally only called in low memory situations) you want to release the view, and since that will result in a dangling pointer you also want to set the pointer to nil. Xcode achieves this by simply using the setter method.

[self setMyView:nil];

The second place, and the place you asked about initially is dealloc. In dealloc you similarly need to release your property although in this case (Main thread only execution, based on the IBOutlet in the question) the dangling pointer should not be a problem. This seems reinforced by Xcode’s automatic implementation of dealloc.

[myView release];

Of course setting the pointer to nil in addition to releasing would not be detrimental at all. And may even be preferable if this were not a main thread only UIKit element. But if you were worried about multi-threading you would likely just use atomic instead.