Loader unable to retain itself during certain configuration change

Question

According to http://developer.android.com/guide/components/loaders.html, one of the nice thing about loader is that, it is able to retain its data during configuration chang

Answer 1

If you are using FragmentManager's replace fragment technique this issue will happen.

When you replace/remove the Fragment, the fragment is detached from the activity and since loaders are attached to the activity, the loaders will be recreated during orientation change.

Try using FragmentManager's hide/show technique. May be this will help you.

Answer 2

My answer is quite straight forward actually. Don't use AsyncTaskLoaders. Because a few bugs regarding AsyncTaskLoaders you knew it by now.

A good combination would be a retainable (setRetainInstance(true) in onActivityCreated()) fragment with AsyncTask. Works the same way. Just have to restructure the code a bit.

---

Message from OP

Although the author doesn't provide any code example, this is the closest workable solution. I do not use the author proposed solution. Instead, I still rely on AsyncTaskLoader for all the necessary loading task. The workaround is that, I will rely on an additional retained fragment, to determine whether I should reconnect/create loader. The is the skeleton code on the whole idea. Works pretty well so far as long as I can tell.

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    ...

    dataRetainedFragment = (DataRetainedFragment)fm.findFragmentByTag(DATE_RETAINED_FRAGMENT);
    // dataRetainedFragment can be null still...
}

@Override
public void onResume() {
    ...
    if (this.data == null) {
        if (dataRetainedFragment != null) {
            // Re-use!
            onLoadFinished(null, dataRetainedFragment);
        } else {
            // Prepare the loader.  Either re-connect with an existing one,
            // or start a new one.
            getLoaderManager().initLoader(0, null, this);
        }
    } else {
    }
}

@Override
public void onLoadFinished(Loader<Data> arg0, Data data) {
    this.data = data;

    if (this.dataRetainedFragment == null) {
        this.dataRetainedFragment = DataRetainedFragment.newInstance(this.data);
        FragmentManager fm = getFragmentManager();
        fm.beginTransaction().add(this.dataRetainedFragment, DATE_RETAINED_FRAGMENT).commitAllowingStateLoss();            
    }

Answer 3

Try to change,

 @Override
public void onResume()
{
    super.onResume();

    if (result == null) {
        // Prepare the loader.  Either re-connect with an existing one,
        // or start a new one.
        getLoaderManager().initLoader(0, null, this);
    } else {
        // Restore from previous state. Perhaps through long pressed home
        // button.
    }
}    

to

 @Override
public void onResume()
{
    super.onResume();

Loader loader = getLoaderManager().getLoader(0); 
if ( loader != null && loader.isReset() ) { 
    getLoaderManager().restartLoader(0, getArguments(), this); 
} else { 
    getLoaderManager().initLoader(0, getArguments(), this); 
} 

}    

Answer 4

I've had success subclassing AsyncTaskLoader and making a few tweaks to its methods.

public class FixedAsyncTaskLoader<D> extends AsyncTaskLoader<D> {

    private D result;

    public FixedAsyncTaskLoader(Context context) {
        super(context);
    }

    @Override
    protected void onStartLoading() {
        if (result != null) {
            deliverResult(result);
        } else {
            forceLoad();
        }
    }

    @Override
    public void deliverResult(T data) {
        result = data;

        if (isStarted()) {
            super.deliverResult(result);
        }
    }

    @Override
    protected void onReset() {
        super.onReset();
        onStopLoading();

        result = null;
    }

    @Override
    protected void onStopLoading() {
        cancelLoad();
    }
}