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Creating a Catalog Browser

Media apps that run on TV need to allow users to browse its content offerings, make a selection, and start playing content. The content browsing experience for apps of this type should be simple and intuitive, as well as visually pleasing and engaging.

This lesson discusses how to use the classes provided by the v17 leanback support library to implement a user interface for browsing music or videos from your app's media catalog.

Create a Media Browse Layout

The BrowseFragment class in the leanback library allows you to create a primary layout for browsing categories and rows of media items with a minimum of code. The following example shows how to create a layout that contains a BrowseFragment:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical"
  >
  <fragment
      android:name="android.support.v17.leanback.app.BrowseFragment"
      android:id="@+id/browse_fragment"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      />
</LinearLayout>

In order to work with this layout in an activity, retrieve the BrowseFragment element from the layout. Use the methods in this class to set display parameters such as the icon, title, and whether category headers are enabled. The following code sample demonstrates how to set the layout parameters for a BrowseFragment in a layout:

public class BrowseMediaActivity extends Activity {
    public static final String TAG ="BrowseActivity";
    protected BrowseFragment mBrowseFragment;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.browse_fragment);
        final FragmentManager fragmentManager = getFragmentManager();
        mBrowseFragment = (BrowseFragment) fragmentManager.findFragmentById(
                R.id.browse_fragment);
        // Set display parameters for the BrowseFragment
        mBrowseFragment.setHeadersState(BrowseFragment.HEADERS_ENABLED);
        mBrowseFragment.setTitle(getString(R.string.app_name));
        mBrowseFragment.setBadgeDrawable(getResources().getDrawable(
                R.drawable.ic_launcher));
        mBrowseFragment.setBrowseParams(params);
    }
}

Displaying Media Lists

The BrowseFragment allows you to define and display browsable media content categories and media items from a media catalog using adapters and presenters. Adapters enable you to connect to local or online data sources that contain your media catalog information. Presenters hold data about media items and provide layout information for displaying an item on screen.

The following example code shows an implementation of a Presenter for displaying string data:

public class StringPresenter extends Presenter {
    private static final String TAG = "StringPresenter";
    public ViewHolder onCreateViewHolder(ViewGroup parent) {
        TextView textView = new TextView(parent.getContext());
        textView.setFocusable(true);
        textView.setFocusableInTouchMode(true);
        textView.setBackground(
                parent.getContext().getResources().getDrawable(R.drawable.text_bg));
        return new ViewHolder(textView);
    }
    public void onBindViewHolder(ViewHolder viewHolder, Object item) {
        ((TextView) viewHolder.view).setText(item.toString());
    }
    public void onUnbindViewHolder(ViewHolder viewHolder) {
        // no op
    }
}

Once you have constructed a presenter class for your media items, you can build and attach an adapter to the BrowseFragment to display those items on screen for browsing by the user. The following example code demonstrates how to construct an adapter to display categories and items in those categories using the StringPresenter class shown in the previous code example:

private ArrayObjectAdapter mRowsAdapter;
private static final int NUM_ROWS = 4;
@Override
protected void onCreate(Bundle savedInstanceState) {
    ...
    buildRowsAdapter();
}
private void buildRowsAdapter() {
    mRowsAdapter = new ArrayObjectAdapter(new ListRowPresenter());
    for (int i = 0; i < NUM_ROWS; ++i) {
        ArrayObjectAdapter listRowAdapter = new ArrayObjectAdapter(
                new StringPresenter());
        listRowAdapter.add("Media Item 1");
        listRowAdapter.add("Media Item 2");
        listRowAdapter.add("Media Item 3");
        HeaderItem header = new HeaderItem(i, "Category " + i, null);
        mRowsAdapter.add(new ListRow(header, listRowAdapter));
    }
    mBrowseFragment.setAdapter(mRowsAdapter);
}

This example shows a static implementation of the adapters. A typical media browsing application uses data from an online database or web service. For an example of a browsing application that uses data retrieved from the web, see the Android TV sample app.

Update the Background

In order to add visual interest to a media-browsing app on TV, you can update the background image as users browse through content. This technique can make interaction with your app feel more cinematic and enjoyable for users.

The Leanback support library provides a BackgroundManager class for changing the background of your TV app activity. The following example shows how to create a simple method for updating the background within your TV app activity:

protected void updateBackground(Drawable drawable) {
    BackgroundManager.getInstance(this).setDrawable(drawable);
}

Many of the existing media-browse apps automatically update the background as the user navigates through media listings. In order to do this, you can set up a selection listener to automatically update the background based on the user's current selection. The following example shows you how to set up an OnItemViewSelectedListener class to catch selection events and update the background:

protected void clearBackground() {
    BackgroundManager.getInstance(this).setDrawable(mDefaultBackground);
}
protected OnItemViewSelectedListener getDefaultItemViewSelectedListener() {
    return new OnItemViewSelectedListener() {
        @Override
        public void onItemSelected(Object item, Row row) {
            if (item instanceof Movie ) {
                URI uri = ((Movie)item).getBackdropURI();
                updateBackground(uri);
            } else {
                clearBackground();
            }
        }
    };
}

Note: The implementation above is a simple example shown for purposes of illustration. When creating this function in your own app, you should consider running the background update action in a separate thread for better performance. In addition, if you are planning on updating the background in response to users scrolling through items, consider adding a time to delay a background image update until the user settles on an item. This technique avoids excessive background image updates.