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"; 
 //進度對話框 
 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); 
  //新建一個對話框，不顯示 
  dialog = new ProgressDialog(this); 
  dialog.setTitle("提示"); 
  dialog.setMessage("正在下載，請稍后..."); 
  dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);//帶有水平滾動條 
  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 
    new MyTask().execute(image_path);//啟動AsyncTask,參數類型為異步類的第一個參數的類型 
   } 
  }); 
 } 
 //創(chuàng)建一個內部類，用來下載圖片 
 public class MyTask extends AsyncTask<String, Integer, Bitmap> { 
  @Override 
  protected void onPreExecute() {//啟動異步類后首先運行，可以設置 
   super.onPreExecute(); 
   dialog.show();//顯示對話框 
  } 
   //第二步，一般進行復雜處理 
  @Override 
  protected Bitmap doInBackground(String... params) {//最重要，復雜處理，后臺，接收execute傳來的參數 
   Bitmap bitmap = null; //二進制圖片 
   //字節(jié)數組輸出流 
   ByteArrayOutputStream outputStream = new ByteArrayOutputStream(); 
   InputStream inputStream = null;//字節(jié)輸入流 
   try { 
    HttpClient httpClient = new DefaultHttpClient();//創(chuàng)建一個Http客戶端 
    HttpGet httpGet = new HttpGet(params[0]);//發(fā)送請求 
    HttpResponse httpResponse = httpClient.execute(httpGet);//返回 
    if (httpResponse.getStatusLine().getStatusCode() == 200) {//成功 
     inputStream = httpResponse.getEntity().getContent();//得到返回內容作為輸入流 
     long file_length = httpResponse.getEntity().getContentLength();//文件長度 
     int len = 0; 
     byte[] data = new byte[1024];//每次讀取的字節(jié) 
     int total_length = 0; 
     // 以字節(jié)的方式讀取圖片數據 
     while ((len = inputStream.read(data)) != -1) { 
      total_length += len; 
      // 計算進度 
      int values = (int) ((total_length / (float) file_length) * 100); 
      // 發(fā)布進度信息 
      publishProgress(values);//發(fā)布進度，AsyncTask第二個參數類型，觸發(fā)onProgressUpdate更新進度條 
      outputStream.write(data, 0, len);//寫入輸出流 
     } 
     byte[] result=outputStream.toByteArray();//將字節(jié)數組輸出流轉換為字節(jié)數組 
     //生成二進制圖片 
     bitmap=BitmapFactory.decodeByteArray(result, 0, result.length); 
    } 
   } catch (Exception e) { 
    e.printStackTrace(); 
   } finally { 
    try { 
     if (inputStream != null) { 
      inputStream.close(); 
     } 
    } catch (Exception e2) { 
    } 
   } 
   return bitmap; 
  } 
  //當有 publishProgress(value)發(fā)來的數據時觸發(fā),更新UI 
  @Override 
  protected void onProgressUpdate(Integer... values) { 
   super.onProgressUpdate(values); 
   // 設置進度對話框的進度值 
   dialog.setProgress(values[0]);//更新進度條，運行在UI 
  } 
  //第四步 
  @Override 
  protected void onPostExecute(Bitmap result) {//下載結束后，隱藏對話框 
   super.onPostExecute(result); 
   dialog.dismiss(); 
   ivImage.setImageBitmap(result); //更新UI，顯示圖片，運行在UI 
  } 
 } 
}