This lesson teaches you to
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.