///************************** // MyClass.m #import "MyClass.h" static MyClass *myClass = NULL; @implementation MyClass (MyClass *)sharedMyClass { myClass = NULL; myClass = [[MyClass alloc] init]; return myClass; } @end Hi Experts, I just want to know myClass is a static ObjC object, it will be automatically released by ARC when no one is referencing it anymore, so no memory leak? is it correct?
Here is an example of a singleton class instance that you can use throughout your app if you need to. It never gets released and is not intended to be released.
@interface MyClass : NSObject + ( MyClass * ) singleton; @end That is the interface, so you'll access it as MyClass.singleton for example. The implementation is like this. The reason for the dispatch_once fluff is to make it safe in an environment where it might be accessed from multiple places all at once.
@implemenation MyClass () + ( MyClass * ) singleton { static MyClass * a; static dispatch_once_t t; dispatch_once ( & t, ^ { a = [[MyClass alloc] init]; } ); return a; } @end Note that this also rely on a static variable. That variable is retained from creation time until forever or the app quits.
static MyClass *myClass creates a reference to the pointer stored into that value. As long as myClass will hold a valid object address, that object will not be deallocated. Basically this variable adds a +1 to the reference count of the stored object. If you want for that object to have a change to deallocate, you'll have to change the value of this variable to point to something else (or back to nil).
As a side note, static in Objective-C has no relation to the static modifier of class members, in C/Objective-C static means a symbol that is not visible to other files, e.g. a fileprivate one from Swift.
dispatch_oncepattern. Here note you have a strong pointer to the class instatic MyClass *myClassso unless you set that tonilit will never be released. But this is not really a leak as, presumably, for this kind of a thing you need some instance of the class ready throughout the life of the app?dispatch_onceas it seems you need a singleton. This is quite normal but typically happens a bit differently to how you do it. Now what you do is fine (and common) also, of course, but sometimes you create a single instance of your class and access it e.g. like the default file manager or standard user preferences or the default notification center. I trust you know which classes I am talking about.