/*
* Copyright 2015 Google Inc. All Rights Reserved.
*
* 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 com.google.android.agera;
import android.support.annotation.NonNull;
/**
* Receives events of the {@link UpdateDispatcher} created with
* {@link Observables#updateDispatcher(ActivationHandler)} when the first {@link Updatable} is
* added
* and the last {@link Updatable} is removed.
*
* <p>Typically an {@link Observable} service implemented using a {@link UpdateDispatcher} only
* needs to be updated if it has clients of its own. By starting to listen to updates from its
* clients on {@link #observableActivated} and stopping on {@link #observableDeactivated}, the
* service of the service can implement an <i>active</i>/<i>inactive</i> lifecycle,
* saving memory and execution time when not needed.
*
* Agera 中抽象出来的 激活处理 接口
* 用于 执行 被观察者 的 激活 和 释放 功能
* 这里的 被观察者 是 UpdateDispatcher
* 因为 UpdateDispatcher 继承了 被观察者（ Observable ）接口 和 观察者（ Updatable ）接口
*/
public interface ActivationHandler {
/**
* Called when the the {@code caller} changes state from having no {@link Updatable}s to
* having at least one {@link Updatable}.
*
* 被观察者 被 激活时
*/
void observableActivated(@NonNull UpdateDispatcher caller);
/**
* Called when the the {@code caller} changes state from having {@link Updatable}s to
* no longer having {@link Updatable}s.
*
* 被观察者 被 释放时
*/
void observableDeactivated(@NonNull UpdateDispatcher caller);
}