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.v4.view;

import android.content.Context;
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 android.support.v4.view.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>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 android.support.v4.view.MenuItem} directly by
 * calling {@link android.support.v4.view.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 android.support.v4.view.MenuItem#setActionProvider(ActionProvider)
 * @see android.support.v4.view.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> A menu item selection is processed in the following order:
     *
     * <ul><li>Receiving a call to
     * {@link android.support.v4.view.MenuItem.OnMenuItemClickListener#onMenuItemClick
     * MenuItem.OnMenuItemClickListener.onMenuItemClick}.</li>
     *
     * <li>Receiving a call to
     * {@link android.support.v4.app.FragmentActivity#onSupportOptionsItemSelected(MenuItem)}
     * FragmentActivity.onSupportOptionsItemSelected(MenuItem)}
     * </li>
     *
     * <li>Receiving a call to
     * {@link android.support.v4.app.Fragment#onSupportOptionsItemSelected(MenuItem)}
     * Fragment.onSupportOptionsItemSelected(MenuItem)}</li>
     *
     * <li>Launching the {@link android.content.Intent} set via
     * {@link android.support.v4.view.MenuItem#setIntent(android.content.Intent)
     * MenuItem.setIntent(android.content.Intent)}
     * </li>
     *
     * <li>Invoking this method.</li></ul>
     *
     * <p>The default implementation does not perform any action and returns false.
     */
    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);
    }
}