Question

In my app the activity which is currently running needs data from an activity which has started it. The parent activity has an object which method needs to be invoked to get the required data.

I am doing like this

In the ParentActivity

public static Puzzle  puzzle;  // Puzzle is a class

In the child activity

Puzzle puzzle = ParentActivity.puzzle;

ArrayList<String> cells = puzzle.getItemList();

It seems to work. But I am not sure about correctness of this approach. It allowed in android.
Will android run-time form destroying the parent activity.

Answer 1

If Puzzle is some plain object representing a data model, what you have is “correct” so long as you consider this to only be a cache and if Puzzle and its contents are fairly small.

Your process can be terminated at any time after it leaves the foreground. At that point, your cached Puzzle vanishes. Any data that needs to survive needs to be stored persistently: file, database, SharedPreferences, “the cloud”, whatever. Your static Puzzle can be a cache of that persistent data, but the real data model is the persistent store, not the cached Puzzle.

Also, static data members represent intentional memory leaks. Anything referenced by that static Puzzle cannot be garbage collected. That works so long as the Puzzle is small. This is also why it is important for Puzzle to be an ordinary Object, not something more complex (e.g., an Activity) — the more complex the object, the more memory you leak.