Android Handling AsyncTask



  • If after the AsyncTask starts there is a screen rotation the owning activity is destroyed and recreated.
  • When the AsyncTask finishes it wants to update the UI that may not valid anymore.


Using Loaders, one can easily overcome the activity destruction/recreation.



public class MainActivity extends AppCompatActivity 
        implements LoaderManager.LoaderCallbacks<Bitmap> {

    //Unique id for the loader
    private static final int MY_LOADER = 0; 

    protected void onCreate(Bundle savedInstanceState) {

        LoaderManager loaderManager = getSupportLoaderManager();

        if(loaderManager.getLoader(MY_LOADER) == null) {
            loaderManager.initLoader(MY_LOADER, null, this).forceLoad();

    public Loader<Bitmap> onCreateLoader(int id, Bundle args) {
        //Create a new instance of your Loader<Bitmap>
        MyLoader loader = new MyLoader(MainActivity.this);
        return loader;

    public void onLoadFinished(Loader<Bitmap> loader, Bitmap data) {
        // do something in the parent activity/service
        // i.e. display the downloaded image
        Log.d("MyAsyncTask", "Received result: ");

    public void onLoaderReset(Loader<Bitmap> loader) {



public class MyLoader extends AsyncTaskLoader<Bitmap> {
    private WeakReference<Activity> motherActivity;

    public MyLoader(Activity activity) {
        //We don't use this, but if you want you can use it, but remember, WeakReference
        motherActivity = new WeakReference<>(activity);

    public Bitmap loadInBackground() {
        // Do work. I.e download an image from internet to be displayed in gui.
        // i.e. return the downloaded gui
        return result;


It is important to use either the v4 compatibility library or not, but do not use part of one and part of the other, as it will lead to compilation errors. To check you can look at the imports for and android.content (you shouldn't have both).