Android IntentService
Posted 胖子luffy
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IntentService是一个含有消息循环的Service,它是一个service,所以service相关具有的特性他都有,同时他还有一些自身的属性,其内部封装了一个消息队列和一个HandlerThread,在其具体的抽象方法:onHandleIntent方法是运行在其消息队列线。
IntentService源代码:
/*
* 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.annotation.WorkerThread;
import android.annotation.Nullable;
import android.content.Intent;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.IBinder;
import android.os.Looper;
import android.os.Message;
/**
* IntentService is a base class for @link Services that handle asynchronous
* requests (expressed as @link Intents) on demand. Clients send requests
* through @link android.content.Context#startService(Intent) calls; the
* service is started as needed, handles each Intent in turn using a worker
* thread, and stops itself when it runs out of work.
*
* <p>This "work queue processor" pattern is commonly used to offload tasks
* from an application's main thread. The IntentService class exists to
* simplify this pattern and take care of the mechanics. To use it, extend
* IntentService and implement @link #onHandleIntent(Intent). IntentService
* will receive the Intents, launch a worker thread, and stop the service as
* appropriate.
*
* <p>All requests are handled on a single worker thread -- they may take as
* long as necessary (and will not block the application's main loop), but
* only one request will be processed at a time.
*
* <div class="special reference">
* <h3>Developer Guides</h3>
* <p>For a detailed discussion about how to create services, read the
* <a href="@docRootguide/components/services.html">Services</a> developer
* guide.</p>
* </div>
*
* @see android.os.AsyncTask
*/
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);
/**
* Creates an IntentService. Invoked by your subclass's constructor.
*
* @param name Used to name the worker thread, important only for debugging.
*/
public IntentService(String name)
super();
mName = name;
/**
* Sets intent redelivery preferences. Usually called from the constructor
* with your preferred semantics.
*
* <p>If enabled is true,
* @link #onStartCommand(Intent, int, int) will return
* @link Service#START_REDELIVER_INTENT, so if this process dies before
* @link #onHandleIntent(Intent) returns, the process will be restarted
* and the intent redelivered. If multiple Intents have been sent, only
* the most recent one is guaranteed to be redelivered.
*
* <p>If enabled is false (the default),
* @link #onStartCommand(Intent, int, int) will return
* @link Service#START_NOT_STICKY, and if the process dies, the Intent
* dies along with it.
*/
public void setIntentRedelivery(boolean enabled)
mRedelivery = enabled;
@Override
public void onCreate()
// TODO: It would be nice to have an option to hold a partial wakelock
// during processing, and to have a static startService(Context, Intent)
// method that would launch the service & hand off a wakelock.
super.onCreate();
HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
thread.start();
mServiceLooper = thread.getLooper();
mServiceHandler = new ServiceHandler(mServiceLooper);
@Override
public void onStart(@Nullable Intent intent, int startId)
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent;
mServiceHandler.sendMessage(msg);
/**
* You should not override this method for your IntentService. Instead,
* override @link #onHandleIntent, which the system calls when the IntentService
* receives a start request.
* @see android.app.Service#onStartCommand
*/
@Override
public int onStartCommand(@Nullable Intent intent, int flags, int startId)
onStart(intent, startId);
return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
@Override
public void onDestroy()
mServiceLooper.quit();
/**
* Unless you provide binding for your service, you don't need to implement this
* method, because the default implementation returns null.
* @see android.app.Service#onBind
*/
@Override
@Nullable
public IBinder onBind(Intent intent)
return null;
/**
* This method is invoked on the worker thread with a request to process.
* Only one Intent is processed at a time, but the processing happens on a
* worker thread that runs independently from other application logic.
* So, if this code takes a long time, it will hold up other requests to
* the same IntentService, but it will not hold up anything else.
* When all requests have been handled, the IntentService stops itself,
* so you should not call @link #stopSelf.
*
* @param intent The value passed to @link
* android.content.Context#startService(Intent).
* This may be null if the service is being restarted after
* its process has gone away; see
* @link android.app.Service#onStartCommand
* for details.
*/
@WorkerThread
protected abstract void onHandleIntent(@Nullable Intent intent);
当启动一个intentService的时候,首先执行到onCreate()方法,代码如下:
@Override
public void onCreate()
// TODO: It would be nice to have an option to hold a partial wakelock
// during processing, and to have a static startService(Context, Intent)
// method that would launch the service & hand off a wakelock.
super.onCreate();
HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
thread.start();
mServiceLooper = thread.getLooper();
mServiceHandler = new ServiceHandler(mServiceLooper);
onCreate方法中new出来一个HandlerThread对象,HandlerThread类继承Thread,是一个含有消息队列的线程,mServiceHandler下面再说。onCreate()执行完后,执行onStartCommand()方法,
@Override
public int onStartCommand(@Nullable Intent intent, int flags, int startId)
onStart(intent, startId);
return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
onStartCommand方法里调用了onStart方法,
@Override
public void onStart(@Nullable Intent intent, int startId)
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
msg.obj = intent;
mServiceHandler.sendMessage(msg);
onStart方法里用到了onCreate中的mServiceHandler, ServiceHandler代码如下:
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);
当执行都onStart方法时,mServiceHandler发送一个消息,ServiceHandler类的handleMessage处理消息,这个时候已经是另外一个线程在处理了,(不清楚的可以了解下HandlerThread)会调用onHandleIntent方法,该方法是一个钩子函数,要用户自己去实现,
/**
* This method is invoked on the worker thread with a request to process.
* Only one Intent is processed at a time, but the processing happens on a
* worker thread that runs independently from other application logic.
* So, if this code takes a long time, it will hold up other requests to
* the same IntentService, but it will not hold up anything else.
* When all requests have been handled, the IntentService stops itself,
* so you should not call @link #stopSelf.
*
* @param intent The value passed to @link
* android.content.Context#startService(Intent).
* This may be null if the service is being restarted after
* its process has gone away; see
* @link android.app.Service#onStartCommand
* for details.
*/
@WorkerThread
protected abstract void onHandleIntent(@Nullable Intent intent);
执行完onHandleIntent后,会主动stopSelf,该服务结束。
- IntentService是一个service,也是一个抽象类;
- 继承IntentService需要实现其onHandlerIntent抽象方法;
- onHandlerIntent在子线程中执行;
- IntentService内部保存着一个HandlerThread、Looper与Handler等成员变量,维护这自身的消息队列;
- 每次IntentService后台任务执行完成之后都会尝试关闭自身,但是当且仅当IntentService消息队列中最后一个消息被执行完成之后才会真正的stop自身;
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