v4/view/ActionProvider.java

/*
 * Copyright (C) 2011 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 android.support.appcompat.view;

import android.content.Context;
import android.view.SubMenu;
import android.view.View;

/**
 * This class is a mediator for accomplishing a given task, for example sharing a file.
 * It is responsible for creating a view that performs an action that accomplishes the task.
 * This class also implements other functions such a performing a default action.
 * <p>
 * An ActionProvider can be optionally specified for a {@link MenuItem} and in such a
 * case it will be responsible for creating the action view that appears in the
 * {@link android.app.ActionBar} as a substitute for the menu item when the item is
 * displayed as an action item. Also the provider is responsible for performing a
 * default action if a menu item placed on the overflow menu of the ActionBar is
 * selected and none of the menu item callbacks has handled the selection. For this
 * case the provider can also optionally provide a sub-menu for accomplishing the
 * task at hand.
 * </p>
 * <p>
 * There are two ways for using an action provider for creating and handling of action views:
 * <ul>
 * <li>
 * Setting the action provider on a {@link MenuItem} directly by calling
 * {@link MenuItem#setActionProvider(ActionProvider)}.
 * </li>
 * <li>
 * Declaring the action provider in the menu XML resource. For example:
 * <pre>
 * <code>
 *   &lt;item android:id="@+id/my_menu_item"
 *     android:title="Title"
 *     android:icon="@drawable/my_menu_item_icon"
 *     android:showAsAction="ifRoom"
 *     android:actionProviderClass="foo.bar.SomeActionProvider" /&gt;
 * </code>
 * </pre>
 * </li>
 * </ul>
 * </p>
 *
 * @see MenuItem#setActionProvider(ActionProvider)
 * @see MenuItem#getActionProvider()
 */
public abstract class ActionProvider {
  private SubUiVisibilityListener mSubUiVisibilityListener;

  /**
   * Creates a new instance.
   *
   * @param context Context for accessing resources.
   */
  public ActionProvider(Context context) {
  }

  /**
   * Factory method for creating new action views.
   *
   * @return A new action view.
   */
  public abstract View onCreateActionView();

  /**
   * Performs an optional default action.
   * <p>
   * For the case of an action provider placed in a menu item not shown as an action this
   * method is invoked if previous callbacks for processing menu selection has handled
   * the event.
   * </p>
   * <p>
   * A menu item selection is processed in the following order:
   * <ul>
   * <li>
   * Receiving a call to {@link MenuItem.OnMenuItemClickListener#onMenuItemClick
   *  MenuItem.OnMenuItemClickListener.onMenuItemClick}.
   * </li>
   * <li>
   * Receiving a call to {@link android.app.Activity#onOptionsItemSelected(MenuItem)
   *  Activity.onOptionsItemSelected(MenuItem)}
   * </li>
   * <li>
   * Receiving a call to {@link android.app.Fragment#onOptionsItemSelected(MenuItem)
   *  Fragment.onOptionsItemSelected(MenuItem)}
   * </li>
   * <li>
   * Launching the {@link android.content.Intent} set via
   * {@link MenuItem#setIntent(android.content.Intent) MenuItem.setIntent(android.content.Intent)}
   * </li>
   * <li>
   * Invoking this method.
   * </li>
   * </ul>
   * </p>
   * <p>
   * The default implementation does not perform any action and returns false.
   * </p>
   */
  public boolean onPerformDefaultAction() {
    return false;
  }

  /**
   * Determines if this ActionProvider has a submenu associated with it.
   *
   * <p>Associated submenus will be shown when an action view is not. This
   * provider instance will receive a call to {@link #onPrepareSubMenu(SubMenu)}
   * after the call to {@link #onPerformDefaultAction()} and before a submenu is
   * displayed to the user.
   *
   * @return true if the item backed by this provider should have an associated submenu
   */
  public boolean hasSubMenu() {
    return false;
  }

  /**
   * Called to prepare an associated submenu for the menu item backed by this ActionProvider.
   *
   * <p>if {@link #hasSubMenu()} returns true, this method will be called when the
   * menu item is selected to prepare the submenu for presentation to the user. Apps
   * may use this to create or alter submenu content right before display.
   *
   * @param subMenu Submenu that will be displayed
   */
  public void onPrepareSubMenu(SubMenu subMenu) {
  }

  /**
   * Notify the system that the visibility of an action view's sub-UI such as
   * an anchored popup has changed. This will affect how other system
   * visibility notifications occur.
   *
   * @hide Pending future API approval
   */
  public void subUiVisibilityChanged(boolean isVisible) {
    if (mSubUiVisibilityListener != null) {
      mSubUiVisibilityListener.onSubUiVisibilityChanged(isVisible);
    }
  }

  /**
   * @hide Internal use only
   */
  public void setSubUiVisibilityListener(SubUiVisibilityListener listener) {
    mSubUiVisibilityListener = listener;
  }

  /**
   * @hide Internal use only
   */
  public interface SubUiVisibilityListener {
    public void onSubUiVisibilityChanged(boolean isVisible);
  }
}