Android TV之谷歌android leanback框架详解

google leanback 库简介

“Leanback” 就是靠着看的意思。是指以放松的姿势倒在沙发上.谷歌推出 android.support.v17.leanback 软件包提供的 API 支持在电视设备上构建用户界面。它为电视应用提供了一些重要的小部件。这个库只支持到api 17以上的版本，也就是andorid 4.2,而一些效果也只是在api-21以上支持。

Demo 介绍

这是两个关于比较官方的Demo地址。有需要的可以下载

以下是Demo的部分截图

接下来就来说说代码结构

MVP的构建模式

Leanback 提供了model-view-presenter mvp的方式来构建应用。

model 是由应用开发者来提供，leanback对于model的实现没有加额外的限制，任何对象都是可以的。
view 还是由原来的android.view包下的类来实现。
Presenter 是基于现在的Adapter的该概念，并扩充为更具的灵活性和组合性。特别的是，绑定数据到view上的操作已经将adapter中分离出去，这部分逻辑由presenter去承担。

不信可以看看它的代码结构

至于MVP的好处这里就不用说了。

视图结构

首先用android Tv的例子来介绍。运行程序时，整体内容被对齐在一个网格布局里。左侧的每一个标题header,都有右侧对应的一个内容行row，他们是一一对应的。header+content row由一个类 ListRow来表示。页面的整体其实是ListRow的集合

整体是一个大的ArrayObjectAdapter 由一系列的ListRow来填充。view的呈现方式由ListRowPresenter来定义。
一个ListRow 由HeaderItem 和一个小的ArrayObjectAdapter组成，这个一行中的ArrayObjectAdapter中放置我们定义的view,呈现方式由CardPresenter来定义。
典型的代码如下：

List<Movie> list = MovieList.setupMovies();mRowsAdapter = new ArrayObjectAdapter(new ListRowPresenter());CardPresenter cardPresenter = new CardPresenter();for (int i = 0; i < NUM_ROWS; i++) {if (i != 0) {Collections.shuffle(list);}ArrayObjectAdapter listRowAdapter = new ArrayObjectAdapter(cardPresenter);for (int j = 0; j < NUM_COLS; j++) {listRowAdapter.add(list.get(j % 5));}HeaderItem header = new HeaderItem(i, MovieList.MOVIE_CATEGORY[i]);mRowsAdapter.add(new ListRow(header, listRowAdapter));}setAdapter(mRowsAdapter);

基本关系：
ArrayObjectAdapter (RowsAdapter) ← A set of ListRow
ListRow = HeaderItem + ArrayObjectAdapter (RowAdapter)
ArrayObjectAdapter (RowAdapter) ← A set of Object (CardInfo/Item)

一些关键点

一版来说，谷歌的leanback 是（如上图）左边的菜单对应后面的一行。但是其实实际在开发中应用中，是左边的一个菜单对应右边一整个页面。第一种情况基本上上面已经说了。下面来说说第二种情况：

public class MainFragment extends BaseBrowseFragment {private static final String TAG = "MainFragment";private static final long HEADER_ID_DISCOVERY = 0;private static final long HEADER_ID_TV_SHOW = 1;private static final long HEADER_ID_FAV = 2;private static final long HEADER_ID_MEDIA = 3;private static final long HEADER_ID_SETTINGS = 4;  // 这些都是对应的左边菜单的id@Overrideprotected int getHeaderTitleArrayRes() {return R.array.main_header_title_array;}@Overrideprotected int getHeaderIconArrayRes() {return R.array.main_header_icon;}@Overrideprotected FragmentFactory getBrowseFragmentFactory() {return new PageRowFragmentFactory(mBackgroundManager);}protected void onEntranceTransitionEnd() {Log.d(TAG, "onEntranceTransitionEnd: ");}private static class PageRowFragmentFactory extends BrowseFragment.FragmentFactory {private final BackgroundManager mBackgroundManager;PageRowFragmentFactory(BackgroundManager backgroundManager) {this.mBackgroundManager = backgroundManager;}@Overridepublic Fragment createFragment(Object rowObj) {Row row = (Row) rowObj;long id = row.getHeaderItem().getId();         //每当点击后就会显示出对应的fragmentmBackgroundManager.setDrawable(null);if (id == HEADER_ID_TV_SHOW) {return new TvShowFragment();} else if (id == HEADER_ID_DISCOVERY) {return new DiscoveryFragment();} else if (id == HEADER_ID_MEDIA) {return new MediaFragment();}else if (id == HEADER_ID_FAV) {return new FavoriteFragment();}else if (id == HEADER_ID_SETTINGS) {return new SettingsFragment();}throw new IllegalArgumentException(String.format("Invalid row %s", rowObj));}}}

在leanback 中，右边页面显示的种类往往不同，例如，有视频列表，图片列表，音乐列表。那么这些在leanback中都是怎么处理的呢？其实在那些列表中的每一个item都是一个Card。然后其实就是在recycleview 中设置不同类型的item。

通过如下的selector 去选择不同的card

public class CardPresenterSelector extends PresenterSelector {private final Context mContext;private final HashMap<Card.Type, Presenter> presenters = new HashMap<Card.Type, Presenter>();public CardPresenterSelector(Context context) {mContext = context;}@Overridepublic Presenter getPresenter(Object item) {if (!(item instanceof Card)) throw new RuntimeException(String.format("The PresenterSelector only supports data items of type '%s'",Card.class.getName()));Card card = (Card) item;Presenter presenter = presenters.get(card.getCardType());if (presenter == null) {switch (card.getCardType()) {case SINGLE_LINE:presenter = new SingleLineCardPresenter(mContext);break;case VIDEO_GRID:presenter = new VideoCardViewPresenter(mContext, R.style.VideoGridCardTheme);break;case MOVIE:presenter = new CardPresenter();break;case MOVIE_COMPLETE:/*** {@link com.smartdevice.multimediaplayer.utils.Constants.ITEM_TYPE_MUSIC}* add for music which use in search and discovery model ,ordinal  =  0*/presenter = new MusicCardPresenter(mContext, false);break;case MUSIC_SMALL:presenter = new MusicCardPresenter(mContext, true);break;case MOVIE_BASE:case SQUARE_BIG:case ICON:presenter = new GridItemPresenter(mContext);break;case GRID_SQUARE:presenter = new GridItemPresenter(mContext);break;case MUSIC_ARTIST:presenter = new ArtistsCirclePresenter(mContext);break;case MUSIC_ALBUM:presenter = new AlbumCardPresenter(mContext);break;case CIRCLE_ICON:presenter = new CircleIconPresenter(mContext);break;case TV_SHOW_CURRENT:case TV_SHOW_UPCOMING:case TV_SHOW_RECOMMENDATION:case TV_SHOW_APP:case SPOTIFY_SEARCH:presenter = new TVShowPresenter(mContext);break;case POPULAR_MUSIC:presenter = new PopularMusicPresenter(mContext);break;case RECOMMEND_VIDEO:case CHILD_CHANNEL:presenter = new RecommendVideoPresenter(mContext);break;case FAVOITE_TVSHOW:presenter = new FavoriteTVShowPresenter(mContext);break;case DEVICE:presenter = new DeviceItemPresenter(mContext);break;case SETTINGS:presenter = new SettingsItemPresenter(mContext);break;case LOCALDEVICE:presenter = new LocalDeviceItemPresenter(mContext);break;case DLNA_DEVICE:presenter = new DlnaDeviceItemPresenter(mContext);break;case LOADING_ICON:presenter = new LoadingCardPresenter(false);break;case LOADING_ICON_ERROR:presenter = new LoadingCardPresenter(true);break;case YOUTUBE_VIDEO_ICON:presenter = new DiscoveryCardViewPresent(mContext);break;default:presenter = new ImageCardViewPresenter(mContext);break;}}presenters.put(card.getCardType(), presenter);return presenter;}

选择好card后，然后对应的card再去往里面填充数据，下面是一种card 类型。

public class MusicCardPresenter extends MusicAbstractCardPresenter<ImageCardView> {public static final String TAG = MusicCardPresenter.class.getSimpleName();public MusicCardPresenter(Context context, int cardThemeResId) {super(new ContextThemeWrapper(context, cardThemeResId));}public MusicCardPresenter(Context context, boolean isSmall) {this(context, isSmall ? R.style.MusicSmallCardStyle : R.style.MusicCardStyle);}@Overrideprotected ImageCardView onCreateView() {ImageCardView imageCardView = new ImageCardView(getContext());imageCardView.setFocusable(true);imageCardView.setFocusableInTouchMode(true);imageCardView.setMainImageScaleType(ImageView.ScaleType.CENTER_CROP);return imageCardView;}@Overridepublic void onBindViewHolder(Card card, ImageCardView cardView) {cardView.setTitleText(card.getTitle());if (TextUtils.isEmpty(card.getFilePath())) {//spotify musicGlide.with(getContext()).load(card.getImageUrl()).into(cardView.getMainImageView());   这里使用Glide 框架来填充图片} else {//local music filesmImageFetcher.loadImage(card.getFilePath(), cardView.getMainImageView());}}@Overridepublic void onUnbindViewHolder(ImageCardView cardView) {super.onUnbindViewHolder(cardView);ImageWorker.cancelWork(cardView.getMainImageView());cardView.setBadgeImage(null);cardView.setMainImage(null);}

如何使用

build.gradle中导入

    implementation 'com.android.support:recyclerview-v7:27.1.0'implementation 'com.android.support:leanback-v17:27.1.0'   //主要是这个implementation 'com.android.support:recommendation:27.1.0'implementation 'com.android.support:preference-leanback-v17:27.1.0'

然后就可以正常调用了。

感谢：Android TV Leanback 简介