android開發步步為營之60:IntentService與Service的區別

標籤：intentservice   service   

         這個面試的時候，相信是面試官最愛的問題之一。簡單的來說，IntentService繼承至Service，Service和Acitivity一樣是依附於應用主進程的，它本身不是一個進程或者一個線程。一些耗時的操作可能會引起ANR的bug，（本文測試的時候，Service執行20秒沒有報ANR），而IntentService，看它的原始碼，onCreate()其實是建立了一個新的線程。

        

/* * 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);}

        Looper對象會每次從MessageQueue中擷取Intent對象，然後Handler處理訊息，調用void onHandleIntent(Intent intent)，在這裡可以執行一些耗時的比如下載檔案等操作。每次調用IntentService都會產生新的HandlerThread，所以不會阻塞UI主線程。如果需要在一個Service裡執行耗時操作，那麼IntentService是一個很好的選擇，不用在Service裡面new Thread()或者New AsyncTask()了那麼麻煩了。下面再看看我們本實驗的demo，對比Service和IntentService對Acitivity的影響。

       第一步：建立Service和IntentService

package com.figo.study.service;import android.app.Service;import android.content.Intent;import android.os.IBinder;public class TestService extends Service {@Overridepublic IBinder onBind(Intent intent) {// TODO Auto-generated method stubreturn null;}@Overridepublic void onCreate() {// TODO Auto-generated method stubsuper.onCreate();}@Overridepublic int onStartCommand(Intent intent, int flags, int startId) {try {Thread.sleep(20000);System.out.print("service執行完成");} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}return super.onStartCommand(intent, flags, startId);}}

/** *  */package com.figo.study.service;import android.app.IntentService;import android.content.Intent;/** * @author Administrator * */public class TestIntentService extends IntentService {//public TestIntentService(String name) {//// TODO Auto-generated constructor stub//super(name);//}public TestIntentService() {super("TestIntentService");}/* (non-Javadoc) * @see android.app.IntentService#onHandleIntent(android.content.Intent) */@Overrideprotected void onHandleIntent(Intent intent) {// TODO Auto-generated method stubtry {Thread.sleep(20000);System.out.print("intentService執行完成");} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

        第二步：AndroidManifest.xml註冊Service和Activity

        <service            android:name="com.figo.study.service.TestService"            android:exported="false" >            <intent-filter>                <action android:name="TestService" />            </intent-filter>        </service>        <service            android:name="com.figo.study.service.TestIntentService"            android:exported="false" >            <intent-filter>                <action android:name="TestIntentService" />            </intent-filter>        </service>        <activity            android:name="com.figo.study.IntentServiceActivity"            android:theme="@android:style/Theme.NoTitleBar" >            <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>

        第三步：建立測試Activity

/** *  */package com.figo.study;import com.figo.study.service.TestIntentService;import com.figo.study.service.TestService;import android.app.Activity;import android.app.IntentService;import android.content.Intent;import android.os.Bundle;/** * @author figo *  */public class IntentServiceActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);try {setContentView(R.layout.activity_intentservice);// 啟動一個20秒逾時的Service，因為是依附在主線程，可以看到必須等service執行完成之後，頁面才會展示出來// Intent service=new Intent("TestService");//Intent service = new Intent(IntentServiceActivity.this,//TestService.class);//startService(service);// 啟動一個20秒逾時的IntentService，因為是建立線程，所以頁面立刻就展示出來了// Intent intentService=new Intent("TestIntentService"); Intent intentService=new Intent(IntentServiceActivity.this,TestIntentService.class); startService(intentService);} catch (Exception e) {e.printStackTrace();}}}

android開發步步為營之60:IntentService與Service的區別