intentservice

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() {@Overridepublic 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() {@Overridepublic 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;//IntentServicepublic 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);}