Question

In an iOS class that will not appear as a view e.g.

@interface MyDataClass : NSObject{}

Is there a method that can be overridden and is consistently called at the end of the classes’ execution/lifecycle similar to viewDidUnload or dealloc, that can call methods safely?

Alternatively how would one go about implementing a method that could recognise the completion of the useful lifespan of such a class?

Answer 1

If you mean a method that runs at the end of lifetime of the Class as a whole (not an instance), I wonder how is the runtime supposed to know when you are done using a class (you can create new instances at any time)? There is an +initialize method, but technically the class itself is available forever (until the program exits).

If you mean the lifetime of an instance, the method you are looking for is -dealloc.

-dealloc is called whenever an object’s internal reference count reaches zero. In non-ARC code, if you override it you must call the superclass’ implementation, so that ultimately NSObject‘s -dealloc is called and that is when the memory is freed.

EDIT: Regarding low memory situations, this is how you register for notifications:

// Somewhere inside the -init method of your class
[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(myMethod:) 
                                             name:UIApplicationDidReceiveMemoryWarningNotification 
                                           object:nil];

Inside dealloc, you MUST do this:

[[NSNotificationCenter defaultCenter] removeObserver:self];

…otherwise, your app may crash.

And of course, you must implement a method with the following signature that will be called on low-memory situations:

- (void) myMethod:(NSNotification*) notification
{
   // Do some cleanup here, perhaps.
}

(otherwise, your app will crash)