core/java/android/view/ViewGroupOverlay.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.annotation.NonNull;
import android.content.Context;
import android.graphics.drawable.Drawable;

/**
 * A group overlay is an extra layer that sits on top of a ViewGroup
 * (the "host view") which is drawn after all other content in that view
 * (including the view group's children). Interaction with the overlay
 * layer is done by adding and removing views and drawables.
 *
 * <p>ViewGroupOverlay is a subclass of {@link ViewOverlay}, adding the ability to
 * manage views for overlays on ViewGroups, in addition to the drawable
 * support in ViewOverlay.</p>
 *
 * @see ViewGroup#getOverlay()
 */
public class ViewGroupOverlay extends ViewOverlay {

    ViewGroupOverlay(Context context, View hostView) {
        super(context, hostView);
    }

    /**
     * Adds a {@code 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.
     *
     * <p>Views in the overlay are visual-only; they do not receive input
     * events and do not participate in focus traversal. Overlay views
     * are intended to be transient, such as might be needed by a temporary
     * animation effect.</p>
     *
     * <p>If the view has a parent, the view will be removed from that parent
     * before being added to the overlay. Also, if that parent is attached
     * in the current view hierarchy, the view will be repositioned
     * such that it is in the same relative location inside the activity. For
     * example, if the view's current parent lies 100 pixels to the right
     * and 200 pixels down from the origin of the overlay's
     * host view, then the view will be offset by (100, 200).</p>
     *
     * <p>{@code View}s added with this API will be drawn in the order they were
     * added. Drawing of the overlay views will happen before drawing of any of the
     * {@code Drawable}s added with {@link #add(Drawable)} API even if a call to
     * this API happened after the call to {@link #add(Drawable)}.</p>
     *
     * <p>Passing <code>null</code> parameter will result in an
     * {@link IllegalArgumentException} being thrown.</p>
     *
     * @param view The {@code View} to be added to the overlay. The added view will be
     * drawn when the overlay is drawn.
     * @see #remove(View)
     * @see ViewOverlay#add(Drawable)
     */
    public void add(@NonNull View view) {
        mOverlayViewGroup.add(view);
    }

    /**
     * Removes the specified {@code View} from the overlay. Passing <code>null</code> parameter
     * will result in an {@link IllegalArgumentException} being thrown.
     *
     * @param view The {@code View} to be removed from the overlay.
     * @see #add(View)
     * @see ViewOverlay#remove(Drawable)
     */
    public void remove(@NonNull View view) {
        mOverlayViewGroup.remove(view);
    }
}