Android Asyntask: Use weak reference for context to avoid device rotate screen

Question

In Apress Pro Android 4 the author has said that:

[...] context of currently running activity will no longer be valid when the device is rotated. [...] One approach is to use a weak reference to the activity instead of a hard reference [...]

But the author just suggest this, and does not tell how it is done. Who has done this before please give me an example.

Solution 1

Somewhere in your AsyncTask you'll want to pass in your activity. Then you'll save that reference in a weak reference. Then you can dereference and use it again in onPostExecute.

Class member:

WeakReference<Activity> weakActivity;

Somewhere in AsyncTask, probably either constructor or onPreExecute:

weakActivity = new WeakReference<Activity>(activity);

In onPostExecute:

Activity activity = weakActivity.get();
if (activity != null) {
   // do your stuff with activity here
}

Solution 2

Here is an example of WeakReference to store a context;

WeakReference<Context> cReference = new WeakReference<Context>(getApplicationContext());

Now we can use this weakReference to do Activity/Context related work.

Solution 3

If you want to restore the previous activity, why not go for onSaveInstanceState and restore it later on.

Check this link for more details

Saving application state

Comments

[q126y]

activity will still be invalid reference if GC didn't kick in time. Please correct me if I am wrong.

[Mahdi-Malv]

does this avoid memory leak?

[Peter Chaula]

The <Activity> in the object definition is not required if language level is set to Java 8

[JensV]

Storing the Application Context in a WeakReference is pretty pointless. The Application Context lives as long as the application does and will never get dereferenced.

[Leo]

WeakReference has a property called isEnqueued (I think) that you can use to determine if the referenced object is enquequed for garbage collection. If it is, then you can assume that object is no longer valid