編輯:關於Android編程
在即時聊天中可能會存在一個隱藏的Bug,這個Bug根據手機的網速和性能有關系,比如你即時聊天中,你發送一消息,你的網絡情況不是很好,這個時候你發送的消息一直處於發送狀態,然後你不想看了,就按退出,這個時候Activity或者Fragment被銷毀的時候就導致了這個消息被強行GC了,所以為了解決這個方案,我們可以使用IntentService,什麼是IntentService?<喎?/kf/ware/vc/" target="_blank" class="keylink">vcD4KPHA+PC9wPgo8cHJlIGNsYXNzPQ=="brush:java;">/*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.*/
從這個解釋中可以看出來是一個異步服務,而且不用擔心他自己的生命周期.所以我們就可以使用它去發送消息,當然消息發送完畢後,我們肯定要通知界面更新UI,這個時候我們就需要使用廣播比較方便些.我們可以這樣寫一個IntentService:
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(); } } }
然後在需要的地方去調用:
UpLoadImgService.startUploadImg(MainActivity.this, "/sdcard/cache/com.softtanck.intentservice/1.png");
還有就是IntentService是繼承的Service,那麼它是怎麼實現異步線程的.?我們先粗略看一下它的源碼:
/* * 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. * *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. * *
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. * * *
Developer Guides
*For a detailed discussion about how to create services, read the * Services developer guide.
* * * @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. * *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. * *
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 + "]");//創建了一個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); }
從源碼中可以看出在OnCreat的時候初始化了一個HandlerThread,然後通過Looper的Loop去從消息隊列裡面去,建立了Handler的通信,而HandlerMessage中調用一個抽象的方法就是我們繼承IntentService中的要實現的方法,該方法就是在線程中的,所以不需要再去開啟線程.它的生命周期也是由Service是管理的.
最近在做一個項目涉及到將包含圖片的簡單網頁下載到本地,方便離線時觀看,在這裡分享一下,大家做下簡單修改就可以用到自己的項目中了。(這裡用到了AQuery庫)復制代碼 代碼
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