Leanback UI toolkit libraries

The Leanback UI toolkit provides some TV-specific libraries exclusive to apps developed for Android TV OS. These libraries include the following:

• Leanback library: provides UI templates that simplify creating Android TV apps.
• Leanback Preferences library: provides preferences and settings screens that are consistent with the platform but can be themed to match your app.
• Leanback Paging library: supports the AndroidX paging model for ObjectAdapters, which are commonly used with the Leanback templates.
• Leanback Tabs library: supports tabbed navigation on Android TV.

Leanback Paging library

Paging inside the Leanback UI toolkit works the same as the AndroidX Paging 3 library, which simplifies adding paging to a RecyclerView.Adapter. With the Leanback Paging library, the adapter that is exposed is typically an ObjectAdapter instead, so the library adds paging support to ObjectAdapter.

To add a paging adapter to your app, first add the library dependency to your project:

implementation "androidx.leanback:leanback-paging:$version"

Then follow the Paging 3 documentation using androidx.leanback.paging.PagingDataAdapter instead of androidx.paging.PagingDataAdapter. The only difference is that you’re now able to pass in a Presenter or PresenterSelector. This works anywhere you would ordinarily use an ObjectAdapter, such as in a ListRow:

val adapter: PagingDataAdapter<MyItem> = PagingDataAdapter(myPresenter,
   object : DiffUtil.ItemCallback<MyItem>() {
       override fun areItemsTheSame(
           oldItem: MyItem,
           newItem: MyItem
       ): Boolean {
           return oldItem.id === newItem.id
       }

       override fun areContentsTheSame(
           oldItem: MyItem,
           newItem: MyItem
       ): Boolean {
           return oldItem == newItem
       }
   })

val header = HeaderItem(headerTitle)
val row = ListRow(header, adapter)

PagingDataAdapter<MyItem> adapter = new PagingDataAdapter(myPresenter, new DiffUtil.ItemCallback<MyItem>() {
    @Override
    public boolean areItemsTheSame(@NonNull MyItem oldItem, @NonNull MyItem newItem) {
        return oldItem.getId().equals(newItem.getId());
    }

    @Override
    public boolean areContentsTheSame(@NonNull MyItem oldItem, @NonNull MyItem newItem) {
        return oldItem.equals(newItem);
    }
});

HeaderItem header = new HeaderItem(headerTitle);
Row row = new ListRow(header, adapter);

Leanback Tabs library

The Leanback UI toolkit templates provide side navigation in the browse screen. To add a row of tabs horizontally across the top of the app, you can instead use Leanback Tabs instead.

Add the library dependency to your project:

implementation "androidx.leanback:leanback-tab:$version"

Then implement tabs using LeanbackTabLayout and LeanbackViewPager by following the existing ViewPager guide. Note that LeanbackViewPager is based on ViewPager, not ViewPager2.

The following is an example:

val leanbackTabLayout = findViewById<LeanbackTabLayout>(R.id.tab_layout)
val leanbackViewPager = findViewById<LeanbackViewPager>(R.id.view_pager)

leanbackViewPager.setAdapter(adapter)
leanbackTabLayout.setupWithViewPager(leanbackViewPager)

LeanbackTabLayout leanbackTabLayout = findViewById(R.id.tab_layout);
LeanbackViewPager leanbackViewPager = findViewById(R.id.view_pager);

leanbackViewPager.setAdapter(adapter);
leanbackTabLayout.setupWithViewPager(leanbackViewPager);

Limitations

The Leanback Tabs library has limitations in the themes it supports and how focus movement is handled.

Supported themes

Only themes that are derived from Theme.AppCompat are supported. TabLayout contains a theme enforcement constraint, which prevents any nondescendant theme of Theme.AppCompat from being used. You can also use the bridge theme for the Leanback UI toolkit.

Focus movement from tabs to top

When the layout height is greater than the screen height and you press the D-pad up button, control moves back to the tab instead of staying inside the fragment and navigating to an item above it (see figure 1). To handle this issue, contents inside the fragment must override focus search; for example, use RowsSupportFragment. BrowseSupportFragment cannot be used inside a tab as it has an overridden focus search method which prevents the focus from moving back to the tab.