Using LoaderCallbacks without Fragment

Question

I am doing some hands-on reading on AsyncTaskLoader so I can use the technique to load the contact list. The only time the code works is when I implement the callbacks from a class that extends Fragment as in MyLoader extends Fragment implements LoaderCallbacks<ArrayList<Contact>>. Is there another way? All I really need is the contact list (name, phone, thumbnail), to send to my backend. When, for example, I try to use Context, since I can get that from any activity by simply doing (Context)this, the code fails to even compile. By context I mean

context.getLoaderManager().initLoader(1, null, this);
//I already changed to Fragment so don't really remember the exact ".context" line.
//But someone who has done this will understand the snippet.

BTW: I am using multiple references. One is http://developer.android.com/reference/android/content/AsyncTaskLoader.html.

QUESTION (again): Can I use AsyncTaskLoader without Fragment or FragmentActivity?

THE CODE THAT WORKS WITH THE FRAGMENT:

package com.example.contactpreload.utils;

import java.util.ArrayList;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.LoaderManager.LoaderCallbacks;
import android.support.v4.content.Loader;

public class LoadingContacts extends Fragment implements LoaderCallbacks<ArrayList<Contact>> {
    ArrayList<Contact> loadedContacts;
    static Fragment fragmentActivity;

    public static LoadingContacts newInstance(int arg) {

        LoadingContacts f = new LoadingContacts();
        Bundle bundle = new Bundle();
        bundle.putInt("index", arg);
        f.setArguments(bundle);
        fragmentActivity = new Fragment();
        return f;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        System.out.println("onCreate()");
        int mIndex = getArguments().getInt("index");
        System.out.println(mIndex);
    }

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

        System.out.println("onActivityCreated()");
        getLoaderManager().initLoader(1, null, this);
    }

    @Override
    public Loader<ArrayList<Contact>> onCreateLoader(int arg0, Bundle arg1) {

        System.out.println("onCreateLoader()");
        return new ContactsLoader(getActivity());
    }

    @Override
    public void onLoadFinished(Loader<ArrayList<Contact>> loader, ArrayList<Contact> data) {
        loadedContacts = data;
        System.out.println("AND THE CONTACTS ARE: ");
        for (Contact c : loadedContacts) {
            System.out.println("NAME: " + c.getName());
            System.out.println("getPhoneNumberHome: " + c.getPhoneNumber());
        }

    }

    @Override
    public void onLoaderReset(Loader<ArrayList<Contact>> arg0) {
        System.out.println("onLoaderReset()");
        // TODO Auto-generated method stub

    }

}



package com.example.contactpreload;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.Menu;

import com.example.contactpreload.utils.LoadingContacts;

public class MainActivity extends FragmentActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        LoadingContacts fragment = LoadingContacts.newInstance(1);
        fragment.setRetainInstance(true);
        getSupportFragmentManager().beginTransaction()
            .add(android.R.id.content, fragment).commit();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

MANIFEST:

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="16" />

Answer 1

AsyncTaskLoader has nothing to do with whether you are using a Fragment or an Activity.

To give you an example, consider a list activity:

public class ExampleActivity extends ListActivity implements
LoaderManager.LoaderCallbacks<Cursor> {

     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.todo_list);

         //to start the loader:
         getLoaderManager().initLoader(0, null, this);
     }

     //override the loader callback methods as usual
     // Creates a new loader after the initLoader () call
     @Override
     public Loader<Cursor> onCreateLoader(int id, Bundle args) {
         CursorLoader cursorLoader = new CursorLoader(this,
         uri, projection, null, null, null);
         return cursorLoader;
     }

     @Override
     public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
         adapter.swapCursor(data);
     }

     @Override
     public void onLoaderReset(Loader<Cursor> loader) {
         // data is not available anymore, delete reference
         adapter.swapCursor(null);
     }
}

Obviously you need to create corresponding adapter for the list view and layout, but the example just shows you how a simple loader for cursor would work for an Activity.

Also, make sure all your import are consistent, either using the support.v4 library, or the regular library:

import android.app.LoaderManager;
import android.content.CursorLoader;
import android.content.Loader;

Another question that is asked, is that if the LoaderCallback interface can be used standalone. This is not recommended if you consider that the LoaderCallback is for.

The LoaderManager.LoaderCallbacks<D> interface is a simple contract that the LoaderManager uses to report data back to the client. What that means, is its only job is to load some data in the background requested by a client, which is effectively, an activity.

If you create a standalone class, you could extend the class definition to implement LoaderManager.LoaderCallbacks<D>, but you will need to report the loaded data back to the original activity through some kind of mechanism, which would complicated a simple task.

Now if you are really fixed on doing this, you could create your standalone class as so:

public class LoadingContacts implements LoaderManager.LoaderCallbacks<Cursor> {
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
    return null;
}

@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
}

@Override
public void onLoaderReset(Loader<Cursor> loader) {
}
}

In your onLoadFinished method, you will need to send the loaded Cursor back through either a broadcast, or some kind of message bus:

• LocalBroadcastManager
• Otto
• Messenger

After you send this information to the MainActivity, you can load it to the adapter and continue as is.