public class MyAsyncTask extends AsyncTask<String,Integer,Integer> {  private Context context;  private NotificationManager notificationManager;  private NotificationCompat.Builder builder;  public MyAsyncTask(Context context){    this.context = context;    notificationManager = (NotificationManager) context.getSystemService(Activity.NOTIFICATION_SERVICE);    builder = new NotificationCompat.Builder(context);  }  @Override  protected void onPreExecute() {    super.onPreExecute();    builder.setSmallIcon(R.mipmap.ic_launcher)        .setContentInfo("下載中...")        .setContentTitle("正在下載");  }  @Override  protected Integer doInBackground(String... params) {    Log.e(TAG, "doInBackground: "+params[0] );    InputStream is = null;    OutputStream os = null;    HttpURLConnection connection = null;    int total_length = 0;    try {      URL url1 = new URL(params[0]);      connection = (HttpURLConnection) url1.openConnection();      connection.setRequestMethod("GET");      connection.setReadTimeout(50000);      connection.connect();      if(connection.getResponseCode() == 200){        is = connection.getInputStream();        os = new FileOutputStream("/sdcard/zongzhi.apk");        byte [] buf = new byte[1024];        int len;        int pro1=0;        int pro2=0;        // 獲取文件流大小，用于更新進度        long file_length = connection.getContentLength();        while((len = is.read(buf))!=-1){          total_length += len;          if(file_length>0) {            pro1 = (int) ((total_length / (float) file_length) * 100);//傳遞進度（注意順序）          }          if(pro1!=pro2) {            // 調用update函數，更新進度            publishProgress(pro2=pro1);          }          os.write(buf, 0, len);        }      }    } catch (MalformedURLException e) {      e.printStackTrace();    } catch (IOException e) {      e.printStackTrace();    }finally {      try {        if (is != null) {          is.close();        }        if (os != null) {          os.close();        }      } catch (IOException e) {        e.printStackTrace();      }      if (connection != null) {        connection.disconnect();      }    }    return total_length;  }  @Override  protected void onCancelled(Integer integer) {    super.onCancelled(integer);  }  @Override  protected void onCancelled() {    super.onCancelled();  }  @Override  protected void onProgressUpdate(Integer... values) {    super.onProgressUpdate(values);    builder.setProgress(100,values[0],false);    notificationManager.notify(0x3,builder.build());    //下載進度提示    builder.setContentText("下載"+values[0]+"%");    if(values[0]==100) {  //下載完成后點擊安裝      Intent it = new Intent(Intent.ACTION_VIEW);      it.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);      it.setDataAndType(Uri.parse("file:///sdcard/zongzhi.apk"), "application/vnd.android.package-archive");      PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, it, PendingIntent.FLAG_UPDATE_CURRENT);      builder.setContentTitle("下載完成")          .setContentText("點擊安裝")          .setContentInfo("下載完成")          .setContentIntent(pendingIntent);      notificationManager.notify(0x3, builder.build());    }  }  @Override  protected void onPostExecute(Integer integer) {    super.onPostExecute(integer);    if(integer == 100) {      Toast.makeText(context, "下載完成", Toast.LENGTH_SHORT).show();    }  }}

//取得系統的下載服務    DownloadManager downloadManager= (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);    //創建下載請求對象    DownloadManager.Request request=new DownloadManager.Request(Uri.parse(downUrl));    request.setDestinationInExternalPublicDir("目錄","文件名");    request.setNotificationVisibility(DownloadManager.Request.NETWORK_MOBILE|DownloadManager.Request.NETWORK_WIFI);    request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);    downloadManager.enqueue(request);