Question

does something need to hold a reference to a singleton objective-c object in order to preserve it through the life of an IOS app?

For example if if AppDelegate you created/instantiated a singleton object but didn’t retain it, would this instance (with instance variable data) be available later on in the iPhone app?

In other words to ensure data in the singleton remains intact, in the App Delegate where it was initially created, would the App Delegate need to retain it to one of it’s instance variables?

Answer 1

No class should need to retain a pointer to a singleton class. Singleton class itself keeps a pointer to its instance. Basically, when the user wants to use a singleton, they will request it through a class method (by convention often starting with shared). This method will check if the singleton has been initialized. If not, it will perform the initialization. If there is already an existing instance in memory, it will just return it. Usually, a singleton object will live in memory for the life of the application.

The point being that, if you set a value for one of the properties, then, yes, it should be accessible in another part of the program. And no, the app delegate does not need to keep a pointer to the singleton.