AsyncTask异步任务类使用

优点：封装了handler+thread+线程池

特点：1、android中已经写好了的多线程

            2、处理UI Thread和worker 

 代码示例：

  KateAsycTask task = new KateAsycTask();task.execute(url,1+"");          class KateAsycTask extends AsyncTask<String, Integer, Bitmap>{private InputStream inputStream;private final String SD_CARD_PATH = Environment.getExternalStorageDirectory().getAbsolutePath().toString();private int maxLength;private FileOutputStream outputStream;/*** 运行在主线程：在异步任务执行之前调用()* 主要做一些初始化*/@Overrideprotected void onPreExecute() {// TODO Auto-generated method stubsuper.onPreExecute();}/*** 在子线程中执行：执行下载任务*/@Overrideprotected Bitmap doInBackground(String... params) {Bitmap bitmap =null;String imageUrl = params[0];//String s = params[1];try {//1,创建urlURL url = new URL(imageUrl);//2,打开链接HttpURLConnection conn = (HttpURLConnection) url.openConnection();//3，设置请求方式conn.setRequestMethod("GET");//4,设置超时时间conn.setConnectTimeout(5000);if(conn.getResponseCode() == 200){maxLength = conn.getContentLength();//设置进度条的最大值pb.setMax(maxLength);inputStream = conn.getInputStream();//为主线程中的imageView设置图片----//bitmap = BitmapFactory.decodeStream(inputStream);String fileName = imageUrl.substring(imageUrl.lastIndexOf("/")+1);outputStream = new FileOutputStream(SD_CARD_PATH+"/"+ fileName);int len = 0;byte[] buffer = new byte[1024];while((len=inputStream.read(buffer))!=-1){outputStream.write(buffer, 0, len);//更新进度条---不能在这里更新：onProgressUpdate//onProgressUpdate(len);publishProgress(len);//触发调用onProgressUpdate}bitmap = BitmapFactory.decodeFile(SD_CARD_PATH+"/"+fileName);}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}finally{try {if(outputStream!=null){outputStream.close();}if(inputStream!=null){inputStream.close();}} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}return bitmap;}/*** 在主线程中执行：接收异步任务下载的进度  更新UI线程的控件*/@Overrideprotected void onProgressUpdate(Integer... values) {pb.setProgress(pb.getProgress()+values[0]);String text = "下载进度:"+100 * pb.getProgress() / maxLength+ "%" ;progressText.setText(text);super.onProgressUpdate(values);}/*** 在主线程中执行：接收异步线程返回的结果*/@Overrideprotected void onPostExecute(Bitmap result) {super.onPostExecute(result);iv_Image.setImageBitmap(result);}/*** 取消异步任务(终止)*/@Overrideprotected void onCancelled() {// TODO Auto-generated method stubsuper.onCancelled();}}

asynctask执行异步任务的源码分析

                                                                    1, public AsyncTask()

初始化了 mWorker(runnable)  mFuture(task)

2, task.execute(Params... params)

executeOnExecutor(sDefaultExecutor, params);

onPreExecute();

exec.execute(mFuture);

sDefaultExecutor.execute(mFuture);

SerialExecutor.execute(mFuture);

mFuture(mWorker).run();

callback.call();

mWorker.call();

doInBackground(mParams)

postResult

通过Handler发送消息：MESSAGE_POST_RESULT

3，InternalHandler extends Handler

MESSAGE_POST_RESULT:

onPostExecute(result);

MESSAGE_POST_PROGRESS

onProgressUpdate(result.mData);

    4,  publishProgress(Progress... values)

sHandler.obtainMessage(MESSAGE_POST_PROGRESS,

                   new AsyncTaskResult<Progress>(this, values)).sendToTarget();

5, 通过线程工厂来 创建线程 ：

ThreadFactory sThreadFactory = new ThreadFactory() {

        private final AtomicInteger mCount = new AtomicInteger(1);

        public Thread newThread(Runnable r) {

            return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());

        }

总结：在AsycTask中存在2个线程池
1，SERIAL_EXECUTOR保存了一个装有异步任务的队列
2，THREAD_POOL_EXECUTOR执行异步任务的线程池