In the previous lesson, you created a catalog browser, implemented in a browse fragment, that displays a list of media items. In this lesson, you create the card views for your media items and present them in the browse fragment.
The BaseCardView
class and subclasses display the metadata associated with a media item. The
ImageCardView
class used in this lesson displays an image for the content along with the media item's title.
See also the sample implementation in the Leanback sample app .
Create a card presenter
A Presenter
generates views and binds objects to them
on demand. In the browse fragment where your app presents its content to the user, you create a
Presenter
for the content cards and pass it to the adapter
that adds the content to the screen. In the following code, the CardPresenter
is created
in the onLoadFinished()
callback of the LoaderManager
:
Kotlin
override fun onLoadFinished(loader: Loader<HashMap<String, List<Movie>>>, data: HashMap<String, List<Movie>>) { rowsAdapter = ArrayObjectAdapter(ListRowPresenter()) val cardPresenter = CardPresenter() var i = 0L data.entries.forEach { entry -> val listRowAdapter = ArrayObjectAdapter(cardPresenter).apply { entry.value.forEach { movie -> add(movie) } } val header = HeaderItem(i, entry.key) i++ rowsAdapter.add(ListRow(header, listRowAdapter)) } val gridHeader = HeaderItem(i, getString(R.string.more_samples)) val gridRowAdapter = ArrayObjectAdapter(GridItemPresenter()).apply { add(getString(R.string.grid_view)) add(getString(R.string.error_fragment)) add(getString(R.string.personal_settings)) } rowsAdapter.add(ListRow(gridHeader, gridRowAdapter)) adapter = rowsAdapter updateRecommendations() }
Java
@Override public void onLoadFinished(Loader<HashMap<String, List<Movie>>> arg0, HashMap<String, List<Movie>> data) { rowsAdapter = new ArrayObjectAdapter(new ListRowPresenter()); CardPresenter cardPresenter = new CardPresenter(); int i = 0; for (Map.Entry<String, List<Movie>> entry : data.entrySet()) { ArrayObjectAdapter listRowAdapter = new ArrayObjectAdapter(cardPresenter); List<Movie> list = entry.getValue(); for (int j = 0; j < list.size(); j++) { listRowAdapter.add(list.get(j)); } HeaderItem header = new HeaderItem(i, entry.getKey()); i++; rowsAdapter.add(new ListRow(header, listRowAdapter)); } HeaderItem gridHeader = new HeaderItem(i, getString(R.string.more_samples)); GridItemPresenter gridPresenter = new GridItemPresenter(); ArrayObjectAdapter gridRowAdapter = new ArrayObjectAdapter(gridPresenter); gridRowAdapter.add(getString(R.string.grid_view)); gridRowAdapter.add(getString(R.string.error_fragment)); gridRowAdapter.add(getString(R.string.personal_settings)); rowsAdapter.add(new ListRow(gridHeader, gridRowAdapter)); setAdapter(rowsAdapter); updateRecommendations(); }
Create a card view
In this step, you build the card presenter with a view holder for the card view that describes your media content items. Note that each presenter must create only one view type. If you have two card view types, then you need two card presenters.
In the Presenter
, implement an
onCreateViewHolder()
callback that creates a view holder that can be used to display a content item:
Kotlin
private const val CARD_WIDTH = 313 private const val CARD_HEIGHT = 176 class CardPresenter : Presenter() { private lateinit var mContext: Context private lateinit var defaultCardImage: Drawable override fun onCreateViewHolder(parent: ViewGroup): Presenter.ViewHolder { mContext = parent.context defaultCardImage = mContext.resources.getDrawable(R.drawable.movie) ...
Java
@Override public class CardPresenter extends Presenter { private Context context; private static int CARD_WIDTH = 313; private static int CARD_HEIGHT = 176; private Drawable defaultCardImage; @Override public ViewHolder onCreateViewHolder(ViewGroup parent) { context = parent.getContext(); defaultCardImage = context.getResources().getDrawable(R.drawable.movie); ...
In the onCreateViewHolder()
method,
create a card view for content items. The following sample uses an
ImageCardView
.
When a card is selected, the default behavior expands it to a larger size. If you want to designate
a different color for the selected card, call setSelected()
as shown here:
Kotlin
... val cardView = object : ImageCardView(context) { override fun setSelected(selected: Boolean) { val selected_background = context.resources.getColor(R.color.detail_background) val default_background = context.resources.getColor(R.color.default_background) val color = if (selected) selected_background else default_background findViewById<View>(R.id.info_field).setBackgroundColor(color) super.setSelected(selected) } } ...
Java
... ImageCardView cardView = new ImageCardView(context) { @Override public void setSelected(boolean selected) { int selected_background = context.getResources().getColor(R.color.detail_background); int default_background = context.getResources().getColor(R.color.default_background); int color = selected ? selected_background : default_background; findViewById(R.id.info_field).setBackgroundColor(color); super.setSelected(selected); } }; ...
When the user opens your app, the Presenter.ViewHolder
displays the CardView
objects for your content items. You need to set these to receive
focus from the D-pad controller by calling setFocusable(true)
and setFocusableInTouchMode(true)
,
as shown in the following code:
Kotlin
... cardView.isFocusable = true cardView.isFocusableInTouchMode = true return ViewHolder(cardView) }
Java
... cardView.setFocusable(true); cardView.setFocusableInTouchMode(true); return new ViewHolder(cardView); }
When the user selects the ImageCardView
, it expands
to reveal its text area with the background color you specify, as shown in figure 1.