Update UI from an AsyncTaskLoader

Question

I\'ve converted my AsyncTask to an AsyncTaskLoader (mostly to deal with configuration changes). I have a TextView I am using as a progres

Answer 1

Emm... you shouldn't be doing this.

because how an anonymous class access parent class Method or Field is by storing an invisible reference to the parent class.

for example you have a Activity:

public class MyActivity
    extends Activity
{
    public void someFunction() { /* do some work over here */ }

    public void someOtherFunction() {
        Runnable r = new Runnable() {
            @Override
            public void run() {
                while (true)
                    someFunction();
            }
        };
        new Thread(r).start(); // use it, for example here just make a thread to run it.
    }
}

the compiler will actually generate something like this:

private static class AnonymousRunnable {
    private MyActivity parent;
    public AnonymousRunnable(MyActivity parent) {
        this.parent = parent;
    }

    @Override
    public void run() {
        while (true)
            parent.someFunction();
    }
}

So, when your parent Activity destroys (due to configuration change, for example), and your anonymous class still exists, the whole activity cannot be gc-ed. (because someone still hold a reference.)

THAT BECOMES A MEMORY LEAK AND MAKE YOUR APP GO LIMBO!!!

If it was me, I would implement the "onProgressUpdate()" for loaders like this:

public class MyLoader extends AsyncTaskLoader {
    private Observable mObservable = new Observable();
    synchronized void addObserver(Observer observer) {
        mObservable.addObserver(observer);
    }
    synchronized void deleteObserver(Observer observer) {
        mObservable.deleteObserver(observer);
    }

    @Override
    public void loadInBackground(CancellationSignal signal)
    {
        for (int i = 0;i < 100;++i)
            mObservable.notifyObservers(new Integer(i));
    }
}

And in your Activity class

public class MyActivity extends Activity {
    private Observer mObserver = new Observer() {
        @Override
        public void update(Observable observable, Object data) {
            final Integer progress = (Integer) data;
            mTextView.post(new Runnable() {
                mTextView.setText(data.toString()); // update your progress....
            });
        }
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreated(savedInstanceState);

        MyLoader loader = (MyLoader) getLoaderManager().initLoader(0, null, this);
        loader.addObserver(mObserver);
    }

    @Override
    public void onDestroy() {
        MyLoader loader = (MyLoader) getLoaderManager().getLoader(0);
        if (loader != null)
            loader.deleteObserver(mObserver);
        super.onDestroy();
    }
}

remember to deleteObserver() during onDestroy() is important, this way the loader don't hold a reference to your activity forever. (the loader will probably be held alive during your Application lifecycle...)