Android异步线程下载图片

package com.jin.test; import java.io.IOException; import java.io.InputStream; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; import android.app.Activity; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.AsyncTask; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.view.View; import android.widget.Button; import android.widget.ImageView; import android.widget.ProgressBar; import android.widget.TextView; public class AsyncTaskTestActivity extends Activity { Button download; ProgressBar pb; ImageView imgPic; TextView tv; Bitmap b; String url = "http://ww1.sinaimg.cn/bmiddle/6834c769jw1djjf4p3p9rj.jpg"; private Handler mHandler = new Handler(){ public void handleMessage(Message msg) { switch (msg.what) { case 1: imgPic.setImageBitmap(b); break; } }; }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); pb=(ProgressBar)findViewById(R.id.pb); tv=(TextView)findViewById(R.id.tv); imgPic = (ImageView) findViewById(R.id.imageView1); download = (Button)findViewById(R.id.download); download.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // DownloadTask dTask = new DownloadTask(); // dTask.execute(100); //imgPic.setImageBitmap(b); Thread t = new Thread(new Runnable(){ @Override public void run() { b=loadRmoteImage(url); Message message = new Message(); message.what = 1; mHandler.sendMessage(message); for(int i=0;i<=100;i++){ pb.setProgress(i); //publishProgress(i); try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } } } }); t.start(); } }); } class DownloadTask extends AsyncTask<Integer, Integer, String>{ //后面尖括号内分别是参数（例子里是线程休息时间），进度(publishProgress用到)，返回值 类型 @Override protected void onPreExecute() { //第一个执行方法 super.onPreExecute(); } @Override protected String doInBackground(Integer... params) { b=loadRmoteImage(url); Message message = new Message(); message.what = 1; mHandler.sendMessage(message); //第二个执行方法,onPreExecute()执行完后执行 for(int i=0;i<=100;i++){ pb.setProgress(i); publishProgress(i); try { Thread.sleep(params[0]); } catch (InterruptedException e) { e.printStackTrace(); } } return "执行完毕"; } @Override protected void onProgressUpdate(Integer... progress) { //这个函数在doInBackground调用publishProgress时触发，虽然调用时只有一个参数 //但是这里取到的是一个数组,所以要用progesss[0]来取值 //第n个参数就用progress[n]来取值 tv.setText(progress[0]+"%"); super.onProgressUpdate(progress); } @Override protected void onPostExecute(String result) { //doInBackground返回时触发，换句话说，就是doInBackground执行完后触发 //这里的result就是上面doInBackground执行后的返回值，所以这里是"执行完毕" setTitle(result); super.onPostExecute(result); } } private Bitmap loadRmoteImage(String imgUrl) { URL fileURL = null; Bitmap bitmap = null; try { fileURL = new URL(imgUrl); } catch (MalformedURLException err) { err.printStackTrace(); } try { HttpURLConnection conn = (HttpURLConnection) fileURL.openConnection(); conn.setDoInput(true); conn.connect(); InputStream is = conn.getInputStream(); int length = (int) conn.getContentLength(); if (length != -1) { byte[] imgData = new byte[length]; byte[] buffer = new byte[512]; int readLen = 0; int destPos = 0; while ((readLen = is.read(buffer)) > 0) { System.arraycopy(buffer, 0, imgData, destPos,readLen); destPos += readLen; } bitmap = BitmapFactory.decodeByteArray(imgData, 0,imgData.length); } } catch (IOException e) { e.printStackTrace(); } return (bitmap); } }