1 Service和IntentService的区别

Service是运行在主线程，不能在Service进行耗时操作否则会有ANR；IntentService内部开启了一个线程，可以执行耗时操作

Service需要手动关闭服务；IntentService在执行完成后会自动关闭服务

IntentService继承自Service，拥有和Service相同的生命周期

2 IntentService详解

IntentService特点：

它创建了一个独立的工作线程来处理所有的通过 onStartCommand() 传递给服务的Intent

创建了一个工作队列，来逐个发送Intent给 onHandleIntent()

不需要主动调用 stopSelf() 结束服务。在所有的Intent被处理完后，系统会自动关闭服务

默认实现的 onBind() 返回null

默认实现的 onStartCommand() 的目的是将Intent插入到工作队列中

继承IntentService需要实现两个函数：构造函数和 onHandleIntent() 函数。

注意：要覆盖IntentService的其他函数时，要通过super调用父类的对应的函数。

IntentService源码概括：

调用 onCreate() 时创建HandlerThread -> 调用 onStart(Intent inent, int startId) 时发送Intent -> onStartCommand(Intent intent, int flags, int startId) 时内部调用了 onStart() 将接收到的Intent发送 -> Handler的 handleMessage() 调用 onHandleIntent(intent) 提供给子类，通过startId作为停止服务标志 stopSelf(startId)

IntentService源码：

/* * Copyright (C) 2008 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.app; import android.content.Intent; import android.os.Handler; import android.os.HandlerThread; import android.os.IBinder; import android.os.Looper; import android.os.Message; public abstract class IntentService extends Service { private volatile Looper mServiceLooper; private volatile ServiceHandler mServiceHandler; private String mName; private boolean mRedelivery; private final class ServiceHandler extends Handler { public ServiceHandler(Looper looper) { super(looper); } @Override public void handleMessage(Message msg) { onHandleIntent((Intent)msg.obj); stopSelf(msg.arg1); } } public IntentService(String name) { super(); mName = name; } public void setIntentRedelivery(boolean enabled) { mRedelivery = enabled; } @Override public void onCreate() { super.onCreate(); HandlerThread thread = new HandlerThread("IntentService[" + mName + "]"); thread.start(); mServiceLooper = thread.getLooper(); mServiceHandler = new ServiceHandler(mServiceLooper); } @Override public void onStart(Intent intent, int startId) { Message msg = mServiceHandler.obtainMessage(); msg.arg1 = startId; msg.obj = intent; mServiceHandler.sendMessage(msg); } @Override public int onStartCommand(Intent intent, int flags, int startId) { onStart(intent, startId); return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY; } @Override public void onDestroy() { mServiceLooper.quit(); } @Override public IBinder onBind(Intent intent) { return null; } protected abstract void onHandleIntent(Intent intent); }