Presenter

abstract class Presenter : FacetProvider

kotlin.Any
↳	androidx.leanback.widget.Presenter

Known Direct Subclasses AbstractDetailsDescriptionPresenter, DetailsOverviewLogoPresenter, DividerPresenter, RowHeaderPresenter, RowPresenter, VerticalGridPresenter AbstractDetailsDescriptionPresenter An abstract Presenter for rendering a detailed description of an item. DetailsOverviewLogoPresenter Presenter that responsible to create a ImageView and bind to DetailsOverviewRow. DividerPresenter DividerPresenter provides a default presentation for DividerRow in HeadersFragment. RowHeaderPresenter RowHeaderPresenter provides a default presentation for HeaderItem using a RowHeaderView and optionally a TextView for description. RowPresenter An abstract Presenter that renders an Object in RowsFragment, the object can be subclass Row or a generic one. VerticalGridPresenter A presenter that renders objects in a VerticalGridView.

Known Indirect Subclasses AbstractMediaItemPresenter, AbstractMediaListHeaderPresenter, DetailsOverviewRowPresenter, FullWidthDetailsOverviewRowPresenter, ListRowPresenter, PlaybackControlsRowPresenter, PlaybackRowPresenter, PlaybackTransportRowPresenter AbstractMediaItemPresenter Abstract Presenter class for rendering media items in a playlist format. AbstractMediaListHeaderPresenter Abstract presenter class for rendering the header for a list of media items in a playlist. DetailsOverviewRowPresenter Renders a DetailsOverviewRow to display an overview of an item. FullWidthDetailsOverviewRowPresenter Renders a DetailsOverviewRow to display an overview of an item. ListRowPresenter ListRowPresenter renders ListRow using a HorizontalGridView hosted in a ListRowView. PlaybackControlsRowPresenter A PlaybackControlsRowPresenter renders a PlaybackControlsRow to display a series of playback control buttons. PlaybackRowPresenter Subclass of RowPresenter that can define the desired behavior when the view reappears. PlaybackTransportRowPresenter A PlaybackTransportRowPresenter renders a PlaybackControlsRow to display a series of playback control buttons.

A Presenter is used to generate Views and bind Objects to them on demand. It is closely related to the concept of an , but is not position-based. The leanback framework implements the adapter concept using ObjectAdapter which refers to a Presenter (or PresenterSelector) instance.

Presenters should be stateless. Presenters typically extend ViewHolder to store all necessary view state information, such as references to child views to be used when binding to avoid expensive calls to View#findViewById(int).

A trivial Presenter that takes a string and renders it into a :

public class StringTextViewPresenter extends Presenter {
      // This class does not need a custom ViewHolder, since it does not use
      // a complex layout.
 
      @Override
      public ViewHolder onCreateViewHolder(ViewGroup parent) {
          return new ViewHolder(new TextView(parent.getContext()));
      }
 
      @Override
      public void onBindViewHolder(ViewHolder viewHolder, Object item) {
          String str = (String) item;
          TextView textView = (TextView) viewHolder.mView;
 
          textView.setText(item);
      }
 
      @Override
      public void onUnbindViewHolder(ViewHolder viewHolder) {
          // Nothing to unbind for TextView, but if this viewHolder had
          // allocated bitmaps, they can be released here.
      }
  }
  

In addition to view creation and binding, Presenter allows dynamic interface (facet) to be added: setFacet(Class, Object). Supported facets:

ItemAlignmentFacet is used by HorizontalGridView and VerticalGridView to customize child alignment.

Summary

Nested classes
open	ViewHolder ViewHolder can be subclassed and used to cache any view accessors needed to improve binding performance (for example, results of findViewById) without needing to subclass a View.
abstract	ViewHolderTask Base class to perform a task on Presenter.

Public constructors
<init>() A Presenter is used to generate Views and bind Objects to them on demand.

Public methods
Any!	getFacet(facetClass: Class<*>!)
abstract Unit	onBindViewHolder(viewHolder: Presenter.ViewHolder!, item: Any!) Binds a View to an item.
open Unit	onBindViewHolder(viewHolder: Presenter.ViewHolder!, item: Any!, payloads: MutableList<Any!>!) Binds a View to an item with a list of payloads.
abstract Presenter.ViewHolder!	onCreateViewHolder(parent: ViewGroup!) Creates a new View.
abstract Unit	onUnbindViewHolder(viewHolder: Presenter.ViewHolder!) Unbinds a View from an item.
open Unit