Presenter

abstract class Presenter : FacetProvider
kotlin.Any
   ↳ androidx.leanback.widget.Presenter

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 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

    Base class to perform a task on Presenter.

    Public constructors

    A Presenter is used to generate Views and bind Objects to them on demand.

    Public methods
    abstract Presenter.ViewHolder!

    Creates a new View.

    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.

    Unit
    setFacet(facetClass: Class<*>!, facetImpl: Any!)

    Sets dynamic implemented facet in addition to basic Presenter functions.

    open Unit

    Called when a view created by this presenter has been detached from its window.

    abstract Unit

    Unbinds a View from an item.

    Any!
    getFacet(facetClass: Class<*>!)

    open Unit

    Called to set a click listener for the given view holder.

    open Unit

    Called when a view created by this presenter has been attached to a window.

    Protected methods
    open static Unit

    Utility method for removing all running animations on a view.

    Public constructors

    <init>

    Presenter()

    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.
  • Public methods

    onCreateViewHolder

    abstract fun onCreateViewHolder(parent: ViewGroup!): Presenter.ViewHolder!

    Creates a new View.

    onBindViewHolder

    abstract fun onBindViewHolder(viewHolder: Presenter.ViewHolder!, item: Any!): Unit

    Binds a View to an item.

    onBindViewHolder

    open fun onBindViewHolder(viewHolder: Presenter.ViewHolder!, item: Any!, payloads: MutableList<Any!>!): Unit

    Binds a View to an item with a list of payloads.

    Parameters
    viewHolder Presenter.ViewHolder!: The ViewHolder which should be updated to represent the contents of the item at the given position in the data set.
    item Presenter.ViewHolder!: The item which should be bound to view holder.
    payloads Presenter.ViewHolder!: A non-null list of merged payloads. Can be empty list if requires full update.

    setFacet

    fun setFacet(facetClass: Class<*>!, facetImpl: Any!): Unit

    Sets dynamic implemented facet in addition to basic Presenter functions.

    Parameters
    facetClass Class<*>!: Facet classes to query, can be class of ItemAlignmentFacet.
    facetImpl Class<*>!: Facet implementation.

    onViewDetachedFromWindow

    open fun onViewDetachedFromWindow(holder: Presenter.ViewHolder!): Unit

    Called when a view created by this presenter has been detached from its window.

    Becoming detached from the window is not necessarily a permanent condition; the consumer of an presenter's views may choose to cache views offscreen while they are not visible, attaching and detaching them as appropriate.

    Any view property animations should be cancelled here or the view may fail to be recycled.
    Parameters
    holder Presenter.ViewHolder!: Holder of the view being detached

    onUnbindViewHolder

    abstract fun onUnbindViewHolder(viewHolder: Presenter.ViewHolder!): Unit

    Unbinds a View from an item. Any expensive references may be released here, and any fields that are not bound for every item should be cleared here.

    getFacet

    fun getFacet(facetClass: Class<*>!): Any!

    setOnClickListener

    open fun setOnClickListener(holder: Presenter.ViewHolder!, listener: OnClickListener!): Unit

    Called to set a click listener for the given view holder. The default implementation sets the click listener on the root view in the view holder. If the root view isn't focusable this method should be overridden to set the listener on the appropriate focusable child view(s).

    Parameters
    holder Presenter.ViewHolder!: The view holder containing the view(s) on which the listener should be set.
    listener Presenter.ViewHolder!: The click listener to be set.

    onViewAttachedToWindow

    open fun onViewAttachedToWindow(holder: Presenter.ViewHolder!): Unit

    Called when a view created by this presenter has been attached to a window.

    This can be used as a reasonable signal that the view is about to be seen by the user. If the adapter previously freed any resources in onViewDetachedFromWindow(ViewHolder) those resources should be restored here.

    Parameters
    holder Presenter.ViewHolder!: Holder of the view being attached

    Protected methods

    cancelAnimationsRecursive

    protected open static fun cancelAnimationsRecursive(view: View!): Unit

    Utility method for removing all running animations on a view.