安卓中实现异步任务的几种方式

问题背景

在安卓日常开发中，经常需要使用到异步任务，现在把安卓中异步任务的几种主要使用方式简单总结一下，后面有需要会对他们每一种进行单独的细致介绍。

问题分析

（1）Thread(Runnable)结合handler实现

实现demo如下：

Handler mHandler = newHandler(){ @Override publicvoid handleMessage(Message msg){ if(msg.what == 1){ textView.setText("Task Done!!"); } } }; mRunnable = new Runnable() { @Override publicvoid run() { // 模拟执行耗时操作 SystemClock.sleep(1000); mHandler.sendEmptyMessage(1); } }; private void startTask(){ // 启动子线程 new Thread(mRunnable).start(); }

（2）结合AsyncTask实现

看下官方给的demo：

private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> { protected Long doInBackground(URL... urls) { int count = urls.length; long totalSize = 0; for (int i = 0; i < count; i++) { totalSize += Downloader.downloadFile(urls[i]); publishProgress((int) ((i / (float) count) * 100)); // Escape early if cancel() is called if (isCancelled()) break; } return totalSize; } protected void onProgressUpdate(Integer... progress) { setProgressPercent(progress[0]); } protected void onPostExecute(Long result) { showDialog("Downloaded " + result + " bytes"); } }

实现AsyncTask的子类，主要实现其 doInBackground（）、onProgressUpdate（）、onPostExecute（）方法。使用时创建对应对象调用即可。代码如下：

new DownloadFilesTask().execute(url1, url2, url3);

（3）基于HandlerThread实现

public class HandlerThreadTest { private final static String TAG = "HandlerThreadTest"; private HandlerThread mHandlerThread = new HandlerThread("myHandlerThread", Process.THREAD_PRIORITY_BACKGROUND); private Handler mHandler = null; public void startHandlerthread(){ mHandlerThread.start(); if (mHandler == null){ mHandler = new Handler(mHandlerThread.getLooper()){ @Override public void handleMessage(@NonNull Message msg) { super.handleMessage(msg); switch (msg.what){ case 1: Log.d(TAG, "收到消息，当前线程：" + Thread.currentThread()); break; } } }; } } public void sendMessage() { Log.d(TAG, "当前线程：" + Thread.currentThread()); Message msg = Message.obtain(); msg.what = 1; mHandler.sendMessage(msg); } }

（4）IntentService的方式实现

我们来看下 IntentService 的主要方法：

@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(@Nullable Intent intent, int startId) { Message msg = mServiceHandler.obtainMessage(); msg.arg1 = startId; msg.obj = intent; mServiceHandler.sendMessage(msg); } 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); } }

我们只需要继承 IntentService，就可以在 onHandlerIntent 方法中异步处理 Intent 类型任务了。

（5）使用线程池来实现

利用 Executors 的静态方法 newCachedThreadPool()、newFixedThreadPool()、newSingleThreadExecutor() 及重载形式实例化 ExecutorService 接口即得到线程池对象。这个有机会后面会单独写篇文章介绍一下。

问题总结

本文大体介绍了安卓开发日常，经常使用到的几种实现异步任务的方案，后面有机会会对每一种单独进行细致的介绍。