AsyncTaskLoader

MainActivity.java

// implement LoaderManager.LoaderCallbacks<String> on MainActivity
public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<String> {
  
  // Create a constant int to uniquely identify loader
  private static final int LOADER_ID = 101;
  
  private static final String KEY = "key";
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // initialize the loader with LOADER_ID as the ID, null for the bundle, and this for the context
    getSupportLoaderManager().initLoader(LOADER_ID, null, this);
  }
  
  private void doSomeFancyLoading() {
    // create a bundle
    Bundle queryBundle = new Bundle();
    
    queryBundle.putString(KEY, "we save this text");

    // call getSupportLoaderManager and store it in a LoaderManager variable
    LoaderManager loaderManager = getSupportLoaderManager();
    
    // get our Loader by calling getLoader and passing the ID we specified
    Loader<String> loader = loaderManager.getLoader(LOADER_ID);
    
    // if the Loader was null, initialize it. Else, restart it.
    if (loader == null)
        loaderManager.initLoader(LOADER_ID, queryBundle, this);
    else
        loaderManager.restartLoader(LOADER_ID, queryBundle, this);
  }
  
  // Override onCreateLoader
  @Override
  public Loader<String> onCreateLoader(int id, final Bundle args) {
    
      // cache result
      private String mResult;
    
      // return a new AsyncTaskLoader<String> as an anonymous inner class with this as the constructor's parameter
      return new AsyncTaskLoader<String>(this) {

          // override onStartLoading
          @Override
          protected void onStartLoading() {
              super.onStartLoading();
              if (args == null) return;
              
              // if mResult != null => deliver result
              if (mResult != null) {
                deliverResult(mResult);
                return;
              }
              forceLoad();
          }

          // override loadInBackground
          @Override
          public String loadInBackground() {
              
              String persistedString = args.getString(KEY);

              if (TextUtils.isEmpty(persistedString)) return null;

              try {
                  // do some long network-related task here
                  return postStringToRestApi(persistedString);
              } catch (IOException e) {
                  e.printStackTrace();
                  return null;
              }
          }
        
          @Override
          public void deliverResult(String data) {
              mResult = data;
              super.deliverResult(mResult);
          }
      };
  }

  // override onLoadFinished
  @Override
  public void onLoadFinished(Loader<String> loader, String data) {
      if (!TextUtils.isEmpty(data)) {
          System.out.println(data);
      } else {
          System.out.prinln("no data was returned");
      }
  }

  // override onLoaderReset
  @Override
  public void onLoaderReset(Loader<String> loader) {

  }
}