core/java/android/view/Overlay.java

/*
 * Copyright (C) 2013 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.view;

import android.graphics.drawable.Drawable;

/**
 * An overlay is an extra layer that sits on top of a View (the "host view") which is drawn after
 * all other content in that view (including children, if the view is a ViewGroup). Interaction
 * with the overlay layer is done in terms of adding/removing views and drawables. Invalidation and
 * redrawing of the overlay layer (and its host view) is handled differently for views versus
 * drawables in the overlay. Views invalidate themselves as usual, causing appropriate redrawing
 * to occur automatically. Drawables, on the other hand, do not manage invalidation, so changes to
 * drawable objects should be accompanied by appropriate calls to invalidate() on the host view.
 *
 * @see android.view.View#getOverlay()
 */
public interface Overlay {

    /**
     * Adds a Drawable to the overlay. The bounds of the drawable should be relative to
     * the host view. Any drawable added to the overlay should be removed when it is no longer
     * needed or no longer visible. There is no automatic invalidation of the host view; changes to
     * the drawable should be accompanied by appropriate invalidation calls to the host view
     * to cause the proper area of the view, and the overlay, to be redrawn.
     *
     * @param drawable The Drawable to be added to the overlay. This drawable will be
     * drawn when the view redraws its overlay.
     * @see #remove(android.graphics.drawable.Drawable)
     * @see #add(View)
     */
    void add(Drawable drawable);

    /**
     * Removes the specified Drawable from the overlay.
     *
     * @param drawable The Drawable to be removed from the overlay.
     * @see #add(android.graphics.drawable.Drawable)
     */
    void remove(Drawable drawable);

    /**
     * Adds a View to the overlay. The bounds of the added view should be relative to
     * the host view. Any view added to the overlay should be removed when it is no longer
     * needed or no longer visible. The view must not be parented elsewhere when it is added
     * to the overlay.
     *
     * @param view The View to be added to the overlay. The added view will be
     * drawn when the overlay is drawn.
     * @see #remove(View)
     * @see #add(android.graphics.drawable.Drawable)
     */
    void add(View view);

    /**
     * Removes the specified View from the overlay.
     *
     * @param view The View to be removed from the overlay.
     * @see #add(View)
     */
    void remove(View view);

    /**
     * Removes all views and drawables from the overlay.
     */
    void clear();
}