提供卡片视图

在上一课中,您创建了一个在浏览 fragment 中实现的目录浏览器,用于显示媒体项列表。在本课中,您将为媒体项创建卡片视图,并将其呈现在浏览 fragment 中。

BaseCardView 类及其子类显示与媒体内容关联的元数据。本课中使用的 ImageCardView 类会显示内容的图片以及媒体项的标题。

本课将介绍 Android TV GitHub 代码库中的 Android Leanback 示例应用中的代码。您可以使用此示例代码启动您自己的应用。

应用卡片视图

图 1. 选中后的 Leanback 示例应用图像卡片视图。

创建卡片 Presenter

Presenter 会生成视图并根据需要将对象绑定到这些视图。在应用向用户显示内容的浏览 fragment 中,您可以为内容卡片创建 Presenter,并将其传递给将内容添加到屏幕的适配器。在以下代码中,在 LoaderManageronLoadFinished() 回调中创建 CardPresenter

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();
}

创建卡片视图

在此步骤中,您将为描述媒体内容项的卡片视图构建包含 ViewHolder 的卡片 Presenter。请注意,每个 Presenter 只能创建一种视图类型。如果您有两种卡片视图类型,则需要两个卡片 Presenter。

Presenter 中,实现一个 onCreateViewHolder() 回调,用于创建可用于显示内容项的 ViewHolder:

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);
...

onCreateViewHolder() 方法中,为内容项创建卡片视图。以下示例使用 ImageCardView

当选中一张卡片时,默认行为会将它展开为更大的尺寸。如果要为所选卡片指定其他颜色,请调用 setSelected(),如下所示:

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);
        }
    };
...

当用户打开您的应用时,Presenter.ViewHolder 会显示内容项的 CardView 对象。您需要通过调用 setFocusable(true)setFocusableInTouchMode(true) 将它们设置为从方向键控制器接收焦点,如以下代码所示:

Kotlin

    ...
    cardView.isFocusable = true
    cardView.isFocusableInTouchMode = true
    return ViewHolder(cardView)
}

Java

...
    cardView.setFocusable(true);
    cardView.setFocusableInTouchMode(true);
    return new ViewHolder(cardView);
}

当用户选择 ImageCardView 时,它会展开即可显示其文本区域(该区域具有您指定的背景颜色),如图 1 所示。