AsyncTaskLoader basic example. (Android)

Question

I am using a Loader in my application and based on the result I get from the query I perform on COntacts using this Loader I perform some calculations and store them back in a Sqlite DB. I want this operation to be Asynchronous, however I am confused between using an Async task, as I have lot of different data types to return or should I use a simple handler or an AsyncTaskLoader, I want it to be simple as I am new to Loaders. I tried to search around for examples of AsyncTaskLoader but it seems rocket science, a basic and simple functional example of any of the three in the context of my scenario would be a lot helpful.

Answer 1

If you wish to use AsyncTaskLoader, here's a nice sample for you.

EDIT: I've decided to make a simpler solution (based on this repo):

public abstract class AsyncTaskLoaderEx<T> extends AsyncTaskLoader<T> {     private static final AtomicInteger sCurrentUniqueId = new AtomicInteger(0);     private T mData;     public boolean hasResult = false;      public static int getNewUniqueLoaderId() {         return sCurrentUniqueId.getAndIncrement();     }      public AsyncTaskLoaderEx(final Context context) {         super(context);         onContentChanged();     }      @Override     protected void onStartLoading() {         if (takeContentChanged())             forceLoad();         //this part should be removed from support library 27.1.0 :         //else if (hasResult)         //    deliverResult(mData);     }      @Override     public void deliverResult(final T data) {         mData = data;         hasResult = true;         super.deliverResult(data);     }      @Override     protected void onReset() {         super.onReset();         onStopLoading();         if (hasResult) {             onReleaseResources(mData);             mData = null;             hasResult = false;         }     }      protected void onReleaseResources(T data) {         //nothing to do.     }      public T getResult() {         return mData;     } } 

Usage:

in your activity:

        getSupportLoaderManager().initLoader(TASK_ID, TASK_BUNDLE, new LoaderManager.LoaderCallbacks<Bitmap>() {             @Override             public Loader<Bitmap> onCreateLoader(final int id, final Bundle args) {                 return new ImageLoadingTask(MainActivity.this);             }              @Override             public void onLoadFinished(final Loader<Bitmap> loader, final Bitmap result) {                 if (result == null)                     return;                 //TODO use result             }              @Override             public void onLoaderReset(final Loader<Bitmap> loader) {             }         }); 

inner static class , or a normal class:

private static class ImageLoadingTask extends AsyncTaskLoaderEx<Bitmap> {      public ImageLoadingTask (Context context) {         super(context);     }      @Override     public Bitmap loadInBackground() {         //TODO load and return bitmap     } } 

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Update: starting from support library 27.1.0, things changed a bit (link here) :

In version 27.1.0, onStartLoading() is called every time the Activity is started. Since you call deliverResult() in onStartLoading(), you trigger onLoadFinished(). This is Working as Intended.

You should remove your call to deliverResult() from onStartLoading() as it is not needed (Loaders already deliver results computed in loadInBackground() without any additional work needed on your part).

I've updated the code above for this change.

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EDIT: Updated, kotlin version can be found here.

Answer 2

Since Honeycomb and the v4 Compatibility Library it is possible to use AsyncTaskLoader. From what I understand, the AsyncTaskLoader can survive through config changes like screen flips. But using AsyncTask you can mess up with configuration changes.

Key information: AsyncTaskLoader is subclass of Loader. This class performs the same function as the AsyncTask, but a bit better, it can also be useful in handling configuration changes (screen orientation).

A very good example and explanation is given here. http://www.javacodegeeks.com/2013/01/android-loaders-versus-asynctask.html

Google has a pretty good example directly in the API Docs. Android Design Patterns provides some more detail and the reasoning behind Loaders.

This tutorial will definetly help You. http://www.javacodegeeks.com/2013/08/android-custom-loader-to-load-data-directly-from-sqlite-database.html