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在即时聊天中可能会存在一个隐藏的Bug,这个Bug根据手机的网速和性能有关系,比如你即时聊天中,你发送一消息,你的网络情况不是很好,这个时候你发送的消息一直处于发送状态,然后你不想看了,就按退出,这个时候Activity或者Fragment被销毁的时候就导致了这个消息被强行GC了,所以为了解决这个方案,我们可以使用IntentService,什么是IntentService?
[java] view plain copy /*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.*/
从这个解释中可以看出来是一个异步服务,而且不用担心他自己的生命周期.所以我们就可以使用它去发送消息,当然消息发送完毕后,我们肯定要通知界面更新UI,这个时候我们就需要使用广播比较方便些.我们可以这样写一个IntentService:
[java] view plain copy package com.softtanck.intentservicedemo.service; import android.app.IntentService; import android.content.Context; import android.content.Intent; import com.softtanck.intentservicedemo.MainActivity; /** * Created by winterfell on 11/17/2015. */ public class UpLoadImgService extends IntentService { public UpLoadImgService() { super("ceshi"); } /** * Creates an IntentService. Invoked by your subclass's constructor. * * @param name Used to name the worker thread, important only for debugging. */ public UpLoadImgService(String name) { super(name); } public static void startUploadImg(Context context, String path) { Intent intent = new Intent(context, UpLoadImgService.class); intent.setAction(MainActivity.UPLOAD_IMG); intent.putExtra(MainActivity.EXTRA_IMG_PATH, path); context.startService(intent); } @Override protected void onHandleIntent(Intent intent) { if (null != intent) { String action = intent.getAction(); if (action.equals(MainActivity.UPLOAD_IMG)) { //UpLoad file uploadImg(intent.getStringExtra(MainActivity.EXTRA_IMG_PATH)); } } } private void uploadImg(String path) { try { Thread.sleep(2000); Intent intent = new Intent(MainActivity.UPLOAD_IMG); intent.putExtra(MainActivity.EXTRA_IMG_PATH, path); sendBroadcast(intent); } catch (InterruptedException e) { e.printStackTrace(); } } }
然后在需要的地方去调用:
[java] view plain copy UpLoadImgService.startUploadImg(MainActivity.this, "/sdcard/cache/com.softtanck.intentservice/1.png");
还有就是IntentService是继承的Service,那么它是怎么实现异步线程的.?我们先粗略看一下它的源码:
[java] view plain copy /* * 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.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. * * <div class="special reference"> * <h3>Developer Guides</h3> * <p>For a detailed discussion about how to create services, read the * <a href="{@docRoot}guide/topics/fundamentals/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 + "]");//创建了一个HandlerThread 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); } /** * 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(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 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)}. */ @WorkerThread protected abstract void onHandleIntent(Intent intent); }
从源码中可以看出在OnCreat的时候初始化了一个HandlerThread,然后通过Looper的Loop去从消息队列里面去,建立了Handler的通信,而HandlerMessage中调用一个抽象的方法就是我们继承IntentService中的要实现的方法,该方法就是在线程中的,所以不需要再去开启线程.它的生命周期也是由Service是管理的.
相关资源：JAVA上百实例源码以及开源项目源代码