Should I null references to Activity Context, when my Activity finishes?

Is it a good practice to null references to Activity Context, when my Activity finishes? I have 3 AsyncTask's, each of them can be running in several instances simultaneously. The update the UI in onPostExecute(). Nulling all Activity Context references in onDestroy() would be quite difficult and mak开发者_如何学编程e the code messy. What is the best thing to do?

Check WeakAsyncTask for an example from Google of an asynctask that doesn't keep references alive beyond the activity lifecycle, and BetterAsyncTask from DroidFu for an example of a way to wire AsyncTasks so they can reconnect to new activity instances (after a rotation, for example); usage example is here.

There's probably not too much harm in keeping the references to Activity around for a short operation (e.g. a single small web request or small file write), but if there's the possibility for the tasks to pile up, it could cause a problem. For example, if your app reads a 200KB XML file from a server on creation, which let's say can takes 1 minute or more over EDGE, a quick flip of the phone open/closed 3 or 4 times could lead to 4 retained Activity instances -- you can run out of memory pretty quickly in this situation, not to mention the duplicated work.

For any really long-running processes, though, you should definitely consider an IntentService instead of an AsyncTask. They're designed for longer-running processes that aren't really tied to a specific activity - like how you can send an MMS and leave the activity to go do other things, and you get a nice happy toast informing you of the completion of the task whenever it finishes.

Do not keep long-lived references to a context-activity (a reference to an activity should have the same life cycle as the activity itself). Try using the context-application instead of a context-activity. Nulling the references is not needed when you do not need the opposite because of the memory troubles.

If the tasks will be eligible for garbage collection themselves shortly after your Activity finishes, I see no problem in keeping the references around.

If the tasks do outlive the activity for a significant amount of time, you should set all references to the Activity Context to null. See also the article Avoiding Memory Leaks.

Either way, it is good practice to use the Application Context (getApplicationContext()) instead of the Activity Context whenever you can. In this case you can't do this, because you need to post UI messages; I'm just mentioning it for completeness.

You can hold context reference using Weak reference. http://developer.android.com/reference/java/lang/ref/WeakReference.html

Weak referenced objects can be GC'd. You should just do check if you context reference is still valid every time you use it.