FacetProvider.java
/*
* Copyright (C) 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
* in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package androidx.leanback.widget;
/**
* This is the query interface to supply optional features(aka facets) on an object without the need
* of letting the object to subclass or implement java interfaces. Facets allow leanback to
* re-compose optional features from leanback ViewHolder to RecyclerView ViewHolder. A typical
* "facet" class is {@link ItemAlignmentFacet} that defines how to align a ViewHolder inside
* VerticalGridView or HorizontalGridView.
* A FacetProvider could be retrieved from two sources by VerticalGridView/HorizontalGridView in
* the following order.
* <li>
* <p>
* ViewHolder based facet:
* </p>
* <p>
* RecyclerView.ViewHolder can implement FacetProvider. If app uses leanback
* Presenter.ViewHolder, the facet of Presenter.ViewHolder will be relayed by
* ItemBridgeAdapter.ViewHolder which is a wrapper of Presenter.ViewHolder.
* ViewHolder based facet is used less frequently than item view type based facet because
* in most cases ViewHolders of same type share the same alignment definition.
* </p>
* <p>
* For example, app calls viewHolder.setFacet(ItemAlignmentFacet.class, itemAlignmentFacet) to
* set alignment of the ViewHolder instance.
* </p>
* </li>
* <li>
* <p>
* RecyclerView item view type based facet:
* </p>
* <p>
* RecyclerView.Adapter can implement {@link FacetProviderAdapter} which returns FacetProvider
* for each item view type. If app uses leanback ObjectAdapter and Presenter, app wraps
* the ObjectAdapter and Presenter using {@link ItemBridgeAdapter}. The implementation of
* {@link ItemBridgeAdapter#getFacetProvider(int)} will return the FacetProvider implemented
* by {@link Presenter} which is mapped to the item view type.
* </p>
* <p>
* For example, app calls presenter.setFacet(ItemAlignmentFacet.class, itemAlignmentFacet) to
* set alignment of all ViewHolders created by this Presenter.
* </p>
* </li>
*/
public interface FacetProvider {
/**
* Queries optional implemented facet.
* @param facetClass Facet classes to query, examples are: class of
* {@link ItemAlignmentFacet}.
* @return Facet implementation for the facetClass or null if feature not implemented.
*/
public Object getFacet(Class<?> facetClass);
}