PresenterLoader

PresenterLoader.java

import android.content.Context;
import android.support.v4.content.Loader;

public final class PresenterLoader<T extends Presenter> extends Loader<T>{

    private final PresenterFactory<T> factory;
    private T presenter;

    public PresenterLoader(Context context, PresenterFactory<T> factory) {
        super(context);
        this.factory = factory;
    }

    @Override
    protected void onStartLoading() {
        // called on activity start

        // if we already own an instance of our presenter, simply deliver it.
        if (presenter != null) {
            deliverResult(presenter);
            return;
        }

        // Otherwise, force a load
        forceLoad();
    }

    @Override
    protected void onForceLoad() {
        // Create the Presenter using the Factory
        presenter = factory.create();

        // Deliver the result
        deliverResult(presenter);
    }

    @Override
    protected void onReset() {
        presenter.onDestroyed();
        presenter = null;
    }
}

Presenter.java

public interface Presenter <V>{
    void onViewAttached(V view);
    void onViewDetached();
    void onDestroyed();
}

PresenterFactory.java

/**
 * Creates a Presenter object.
 * @param <T> presenter type
 */
public interface PresenterFactory<T extends Presenter> {
    T create();
}

SampleActivity.java

import android.os.Bundle;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.Loader;
import android.support.v7.app.AppCompatActivity;

import de.czyrux.countrykata.ui.presenter.PresenterLoader;

public class SampleActivity extends AppCompatActivity implements SomeView, LoaderManager.LoaderCallbacks<SomePresenter> {

    private static final int LOADER_ID = 101;
    private SomePresenter presenter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // initialization code...

        getSupportLoaderManager().initLoader(LOADER_ID, null, this);
    }

    @Override
    protected void onStart() {
        super.onStart();

        // Ready to use presenter
        presenter.onViewAttached(this);
    }

    @Override
    protected void onStop() {
        presenter.onViewDetached();
        super.onStop();
    }

    // Some other activity code and view interface implementation...


    @Override
    public Loader<SomePresenter> onCreateLoader(int id, Bundle args) {
        return new PresenterLoader<>(this, new SomePresenterFactory());
    }

    @Override
    public void onLoadFinished(Loader<SomePresenter> loader, SomePresenter presenter) {
        this.presenter = presenter;
    }

    @Override
    public void onLoaderReset(Loader<SomePresenter> loader) {
        presenter = null;
    }
}