public class AsyncTaskActivity2 extends Activity { 
 private Button btnDown;//圖片框 
 private ImageView ivImage;//圖片URL 
 private static String image_path = "http://www.wfu.edu.cn/page/main1406/images/nav2.jpg"; 
 //進(jìn)度對(duì)話框 
 private ProgressDialog dialog; 
 @Override 
 protected void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.asynctask_activity); 
  btnDown = (Button) findViewById(R.id.btnDown); 
  ivImage = (ImageView) findViewById(R.id.ivSinaImage); 
  //新建一個(gè)對(duì)話框，不顯示 
  dialog = new ProgressDialog(this); 
  dialog.setTitle("提示"); 
  dialog.setMessage("正在下載，請(qǐng)稍后..."); 
  dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);//帶有水平滾動(dòng)條 
  dialog.setCancelable(false);//不能 
  //單擊按鈕后執(zhí)行AsyncTask，并傳入圖片URL 
  btnDown.setOnClickListener(new View.OnClickListener() { 
   @Override 
   public void onClick(View v) { 
    // 執(zhí)行異步任務(wù) 
    new MyTask().execute(image_path);//啟動(dòng)AsyncTask,參數(shù)類型為異步類的第一個(gè)參數(shù)的類型 
   } 
  }); 
 } 
 //創(chuàng)建一個(gè)內(nèi)部類，用來(lái)下載圖片 
 public class MyTask extends AsyncTask<String, Integer, Bitmap> { 
  @Override 
  protected void onPreExecute() {//啟動(dòng)異步類后首先運(yùn)行，可以設(shè)置 
   super.onPreExecute(); 
   dialog.show();//顯示對(duì)話框 
  } 
   //第二步，一般進(jìn)行復(fù)雜處理 
  @Override 
  protected Bitmap doInBackground(String... params) {//最重要，復(fù)雜處理，后臺(tái)，接收execute傳來(lái)的參數(shù) 
   Bitmap bitmap = null; //二進(jìn)制圖片 
   //字節(jié)數(shù)組輸出流 
   ByteArrayOutputStream outputStream = new ByteArrayOutputStream(); 
   InputStream inputStream = null;//字節(jié)輸入流 
   try { 
    HttpClient httpClient = new DefaultHttpClient();//創(chuàng)建一個(gè)Http客戶端 
    HttpGet httpGet = new HttpGet(params[0]);//發(fā)送請(qǐng)求 
    HttpResponse httpResponse = httpClient.execute(httpGet);//返回 
    if (httpResponse.getStatusLine().getStatusCode() == 200) {//成功 
     inputStream = httpResponse.getEntity().getContent();//得到返回內(nèi)容作為輸入流 
     long file_length = httpResponse.getEntity().getContentLength();//文件長(zhǎng)度 
     int len = 0; 
     byte[] data = new byte[1024];//每次讀取的字節(jié) 
     int total_length = 0; 
     // 以字節(jié)的方式讀取圖片數(shù)據(jù) 
     while ((len = inputStream.read(data)) != -1) { 
      total_length += len; 
      // 計(jì)算進(jìn)度 
      int values = (int) ((total_length / (float) file_length) * 100); 
      // 發(fā)布進(jìn)度信息 
      publishProgress(values);//發(fā)布進(jìn)度，AsyncTask第二個(gè)參數(shù)類型，觸發(fā)onProgressUpdate更新進(jìn)度條 
      outputStream.write(data, 0, len);//寫(xiě)入輸出流 
     } 
     byte[] result=outputStream.toByteArray();//將字節(jié)數(shù)組輸出流轉(zhuǎn)換為字節(jié)數(shù)組 
     //生成二進(jìn)制圖片 
     bitmap=BitmapFactory.decodeByteArray(result, 0, result.length); 
    } 
   } catch (Exception e) { 
    e.printStackTrace(); 
   } finally { 
    try { 
     if (inputStream != null) { 
      inputStream.close(); 
     } 
    } catch (Exception e2) { 
    } 
   } 
   return bitmap; 
  } 
  //當(dāng)有 publishProgress(value)發(fā)來(lái)的數(shù)據(jù)時(shí)觸發(fā),更新UI 
  @Override 
  protected void onProgressUpdate(Integer... values) { 
   super.onProgressUpdate(values); 
   // 設(shè)置進(jìn)度對(duì)話框的進(jìn)度值 
   dialog.setProgress(values[0]);//更新進(jìn)度條，運(yùn)行在UI 
  } 
  //第四步 
  @Override 
  protected void onPostExecute(Bitmap result) {//下載結(jié)束后，隱藏對(duì)話框 
   super.onPostExecute(result); 
   dialog.dismiss(); 
   ivImage.setImageBitmap(result); //更新UI，顯示圖片，運(yùn)行在UI 
  } 
 } 
}