之前写过一篇文章讲AsyncTask入门的，http://blog.csdn.net/lincyang/article/details/6617802。
今天要说的IntentService提供的功能也很类似，都是来处理异步工作的。
工作流程也非常简单，客户端通过startService(Intent) 方法来调用，服务启动后，开启worker线程来顺序处理intent的任务。注意这里，一个intentService可以处理多个任务，只不过是一个接着一个的顺序来处理的；AsyncTask通常情况是每个任务启动一个新的asycnTask来工作，一个asyncTask只能使用一次，当你想再次使用的话，只好再new一个任务，否则要报异常的。从表象上看，这是两者的区别。当任务完成后，IntentService自动停止。
IntentService是继承自Service的，从源码上看，它是Service、HandlerThread和Handler的强强联合。源码也比AsyncTask简单，有兴趣的童鞋可以去看看。
下面说说它的用法，和AsyncTask一样，使用IntentService必须要写一个类然后继承它。
因为IntentService本身是继承自Service，所以在使用的时候要先在AndroidManifest.xml中注册，否则报错：Unable to start service Intent not found
IntentService有7个方法，其中最重要的是onHandleIntent()，在这里调用worker线程来处理工作，每次只处理一个intent，像上面描述的，如果有多个，它会顺序处理，直到最后一个处理完毕，然后关闭自己。一点都不用我们操心，多好。
再介绍另一个很有意思的方法，setIntentRedelivery()。从字面理解是设置intent重投递。如果设置为true，onStartCommand(Intent, int, int)将会返回START_REDELIVER_INTENT，如果onHandleIntent(Intent)返回之前进程死掉了，那么进程将会重新启动，intent重新投递，如果有大量的intent投递了，那么只保证最近的intent会被重投递。这个机制也很好，大家可以尝试着用。
下面写个小例子，这个例子和之前asyncTask的一样，都是模拟处理耗时任务的。这里加上了广播机制来传递消息。
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.linc.TestIntentService"
android:versionCode="1"
android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".TestIntentService"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<service android:name=".LincIntentService"></service>
</application>
</manifest>
xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:id="@+id/text"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textSize="30sp"
android:textColor="#FF0000"
android:text="@string/hello"
/>
<Button
android:id="@+id/btnStart"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Start"
/>
<Button
android:id="@+id/btnSendOther"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="SendOtherBroadcast"
/>
</LinearLayout>
Activity
package com.linc.TestIntentService;
import android.app.Activity;
import android.app.IntentService;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.os.SystemClock;
import android.text.format.DateFormat;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class TestIntentService extends Activity {
private final static String Tag="TestIntentService";
private TextView text;
private Button btnStart;
private Button btnSendOther;
private MessageReceiver receiver ;
/*
* Action
*/
private static final String ACTION_RECV_MSG = "com.linc.intent.action.RECEIVE_MESSAGE";
private static final String ACTION_OTHER_MSG = "com.linc.intent.action.OTHER_MESSAGE";
/*
* Message
*/
private static final String MESSAGE_IN="message_input";
private static final String MESSAGE_OUT="message_output";
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
text=(TextView)findViewById(R.id.text);
text.setText("准备");
btnStart=(Button)findViewById(R.id.btnStart);
btnStart.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent msgIntent = new Intent(TestIntentService.this,
LincIntentService.class);
msgIntent.putExtra(MESSAGE_IN, text.getText().toString());
startService(msgIntent);
}
});
btnSendOther=(Button)findViewById(R.id.btnSendOther);
btnSendOther.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
});
//动态注册receiver
IntentFilter filter = new IntentFilter(ACTION_RECV_MSG);
filter.addCategory(Intent.CATEGORY_DEFAULT);
receiver = new MessageReceiver();
registerReceiver(receiver, filter);
IntentFilter filter2 = new IntentFilter(ACTION_OTHER_MSG);
filter2.addCategory(Intent.CATEGORY_DEFAULT);
receiver = new MessageReceiver();
registerReceiver(receiver, filter2);
}
//广播来接收
public class MessageReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
String message = intent.getStringExtra(MESSAGE_OUT);
text.setText(message);
Toast.makeText(context, "message",
Toast.LENGTH_SHORT).show();
}
}
}
IntentService
package com.linc.TestIntentService;
import android.app.IntentService;
import android.content.Intent;
import android.os.IBinder;
import android.os.SystemClock;
import android.text.format.DateFormat;
import android.util.Log;
//IntentService
public class LincIntentService extends IntentService {
/*
* Action
*/
private static final String ACTION_RECV_MSG = "com.linc.intent.action.RECEIVE_MESSAGE";
private static final String ACTION_OTHER_MSG = "com.linc.intent.action.OTHER_MESSAGE";
/*
* Message
*/
private static final String MESSAGE_IN="message_input";
private static final String MESSAGE_OUT="message_output";
private final static String Tag="---LincIntentService";
public LincIntentService() {
super("LincIntentService");
Log.d(Tag, "Constructor");
}
@Override
public IBinder onBind(Intent intent) {
Log.d(Tag, "onBind()");
return super.onBind(intent);
}
@Override
public void onCreate() {
Log.d(Tag, "onCreate()");
super.onCreate();
}
@Override
public void onDestroy() {
Log.d(Tag, "onDestroy()");
super.onDestroy();
}
@Override
public void onStart(Intent intent, int startId) {
Log.d(Tag, "onStart()");
super.onStart(intent, startId);
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Log.d(Tag, "onStartCommand()");
return super.onStartCommand(intent, flags, startId);
}
@Override
public void setIntentRedelivery(boolean enabled) {
Log.d(Tag, "setIntentRedelivery()");
super.setIntentRedelivery(enabled);
}
@Override
protected void onHandleIntent(Intent intent) {
Log.d(Tag, "LincIntentService is onHandleIntent!");
String msgRecv = intent.getStringExtra(MESSAGE_IN);
for (int i = 0; i < 5; i++) {
String resultTxt = msgRecv + " "
+ DateFormat.format("MM/dd/yy hh:mm:ss", System.currentTimeMillis());
Intent broadcastIntent = new Intent();
broadcastIntent.setAction(ACTION_RECV_MSG);
broadcastIntent.addCategory(Intent.CATEGORY_DEFAULT);
broadcastIntent.putExtra(MESSAGE_OUT, resultTxt);
sendBroadcast(broadcastIntent);
SystemClock.sleep(1000);
}
}
// <service android:name=".LincIntentService"></service>
}
从这两篇文章中可以看到，andorid提供这两个处理耗时任务的工具，为我们开发者带来了极大的便利。跟随源码，又可以让我们的水平上升一个档次。看来，android提供的文档和例子就是一个宝库，我们要好好的利用起来！
附上源码
/*
* 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;
/**
* IntentService is a base class for {@link Service}s that handle asynchronous
* requests (expressed as {@link Intent}s) 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.
*
* @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(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;
}
/**
* 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.
*
* @param intent The value passed to {@link
* android.content.Context#startService(Intent)}.
*/
protected abstract void onHandleIntent(Intent intent);
}