android/content/ComponentCallbacks.java

/*
 * Copyright (C) 2006 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.content;

import android.annotation.NonNull;
import android.content.res.Configuration;

/**
 * The set of callback APIs that are common to all application components
 * ({@link android.app.Activity}, {@link android.app.Service},
 * {@link ContentProvider}, and {@link android.app.Application}).
 *
 * <p class="note"><strong>Note:</strong> You should also implement the {@link
 * ComponentCallbacks2} interface, which provides the {@link
 * ComponentCallbacks2#onTrimMemory} callback to help your app manage its memory usage more
 * effectively.</p>
 */
public interface ComponentCallbacks {
    /**
     * Called by the system when the device configuration changes while your
     * component is running.  Note that, unlike activities, other components
     * are never restarted when a configuration changes: they must always deal
     * with the results of the change, such as by re-retrieving resources.
     *
     * <p>At the time that this function has been called, your Resources
     * object will have been updated to return resource values matching the
     * new configuration.
     *
     * <p>For more information, read <a href="{@docRoot}guide/topics/resources/runtime-changes.html"
     * >Handling Runtime Changes</a>.
     *
     * @param newConfig The new device configuration.
     */
    void onConfigurationChanged(@NonNull Configuration newConfig);

    /**
     * This is called when the overall system is running low on memory, and
     * actively running processes should trim their memory usage.  While
     * the exact point at which this will be called is not defined, generally
     * it will happen when all background process have been killed.
     * That is, before reaching the point of killing processes hosting
     * service and foreground UI that we would like to avoid killing.
     *
     * <p>You should implement this method to release
     * any caches or other unnecessary resources you may be holding on to.
     * The system will perform a garbage collection for you after returning from this method.
     * <p>Preferably, you should implement {@link ComponentCallbacks2#onTrimMemory} from
     * {@link ComponentCallbacks2} to incrementally unload your resources based on various
     * levels of memory demands.  That API is available for API level 14 and higher, so you should
     * only use this {@link #onLowMemory} method as a fallback for older versions, which can be
     * treated the same as {@link ComponentCallbacks2#onTrimMemory} with the {@link
     * ComponentCallbacks2#TRIM_MEMORY_COMPLETE} level.</p>
     */
    void onLowMemory();
}