Create a new Android application project. Configure the app as shown in Figure 25.3.

Figure 25.3  Creating PhotoGallery

Click Next. When prompted, check Phone and Tablet as the target form factor and choose API 19: Android 4.4 (KitKat) from the Minimum SDK dropdown.

Then have the wizard create an empty activity named PhotoGalleryActivity.

PhotoGallery will follow the same architecture you have been using so far. PhotoGalleryActivity will be a SingleFragmentActivity subclass and its view will be the container view defined in activity_fragment.xml. This activity will host a fragment – in particular, an instance of PhotoGalleryFragment, which you will create shortly.

Copy SingleFragmentActivity.java and activity_fragment.xml into your project from a previous project.

In PhotoGalleryActivity.java, set up PhotoGalleryActivity as a SingleFragmentActivity by deleting the code that the template generated and replacing it with an implementation of createFragment(). Have createFragment() return an instance of PhotoGalleryFragment. (Bear with the error that this code will cause for the moment. It will go away after you create the PhotoGalleryFragment class.)

public class PhotoGalleryActivity extends Activity SingleFragmentActivity {

    @Override
    protected Fragment createFragment() {
        return PhotoGalleryFragment.newInstance();
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        /* Auto-generated template code... */
    }

}

PhotoGallery will display its results in a RecyclerView, using the built-in GridLayoutManager to arrange the items in a grid.

First, add the RecyclerView library as a dependency, as you did in Chapter 8. Open the project structure window and select the app module on the left. Select the Dependencies tab and click the + button. Select Library dependency from the drop-down menu that appears. Find and select the recyclerview-v7 library and click OK.

Rename layout/activity_photo_gallery.xml to layout/fragment_photo_gallery.xml to create a layout for the fragment. Then replace its contents with the RecyclerView shown in Figure 25.4.

Figure 25.4  A RecyclerView (layout/fragment_photo_gallery.xml)

Finally, create the PhotoGalleryFragment class. Retain the fragment, inflate the layout you just created, and initialize a member variable referencing the RecyclerView.

public class PhotoGalleryFragment extends Fragment {

    private RecyclerView mPhotoRecyclerView;

    public static PhotoGalleryFragment newInstance() {
        return new PhotoGalleryFragment();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setRetainInstance(true);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_photo_gallery, container, false);

        mPhotoRecyclerView = (RecyclerView) v.findViewById(R.id.photo_recycler_view);
        mPhotoRecyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 3));

        return v;
    }
}

(Wondering why you are retaining the fragment? Hold that thought – we will explain later in the chapter, in the section called Cleaning Up AsyncTasks.)

Fire up PhotoGallery to make sure everything is wired up correctly before moving on. If all is well, you will be the proud owner of a blank screen.