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:$version"
Then follow the
Paging 3 documentation using
androidx.leanback.paging.PagingDataAdapter
instead of
androidx.paging.PagingDataAdapter
. The only difference is that you’re now able
to pass in a Presenter
or
PresenterSelector
.
This works anywhere you would ordinarily use an ObjectAdapter
, such as in a
ListRow
:
Kotlin
val adapter: PagingDataAdapter<MyItem> = PagingDataAdapter(myPresenter, object : DiffUtil.ItemCallback<MyItem>() { override fun areItemsTheSame( oldItem: MyItem, newItem: MyItem ): Boolean { return oldItem.id === newItem.id } override fun areContentsTheSame( oldItem: MyItem, newItem: MyItem ): Boolean { return oldItem == newItem } }) val header = HeaderItem(headerTitle) val row = ListRow(header, adapter)
Java
PagingDataAdapter<MyItem> adapter = new PagingDataAdapter(myPresenter, new DiffUtil.ItemCallback<MyItem>() { @Override public boolean areItemsTheSame(@NonNull MyItem oldItem, @NonNull MyItem newItem) { return oldItem.getId().equals(newItem.getId()); } @Override public boolean areContentsTheSame(@NonNull MyItem oldItem, @NonNull MyItem newItem) { return oldItem.equals(newItem); } }); HeaderItem header = new HeaderItem(headerTitle); Row row = new ListRow(header, adapter);
Leanback Tabs library
The Leanback UI toolkit templates provide side navigation in the browse screen. To add a row of tabs horizontally across the top of the app, you can instead use Leanback Tabs instead.
Add the library dependency to your project:
implementation "androidx.leanback:leanback-tab:$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:
Kotlin
val leanbackTabLayout = findViewById<LeanbackTabLayout>(R.id.tab_layout) val leanbackViewPager = findViewById<LeanbackViewPager>(R.id.view_pager) leanbackViewPager.setAdapter(adapter) leanbackTabLayout.setupWithViewPager(leanbackViewPager)
Java
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.