android教程之使用asynctask在后台运行耗时任务

private class DownloadDBTask extends AsyncTask<String, Integer, String> {  
        // 可变长的输入参数，与AsyncTask.exucute()对应  
        ProgressDialog pdialog;  
        public DownloadDBTask(Context context){  
            pdialog = new ProgressDialog(context, 0);     
            pdialog.setButton("取消", new DialogInterface.OnClickListener() {  
             public void onClick(DialogInterface dialog, int i) {  
              dialog.cancel();  
             }  
            });  
            pdialog.setOnCancelListener(new DialogInterface.OnCancelListener() {  
             public void onCancel(DialogInterface dialog) {  
              finish();  
             }  
            });
            pdialog.setTitle("第一次使用，正在下载数据...");
            pdialog.setCancelable(true);  
            pdialog.setMax(100);  
            pdialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);  
            pdialog.show();  
        }

        @Override 
        protected String doInBackground(String... params) {  
            try{
                    if (DataOper.GetTopNearestPOIs(1, mDBHelper).size()==0)
                            DataOper.GetAllPtsFromNet(mDBHelper, pdialog); // 从网络上下载数据记录的功能
            } catch(Exception e) {  
                    e.printStackTrace();
            }  
            return null;
        }

        @Override 
        protected void onCancelled() {  
            super.onCancelled();  
        }  

        @Override 
        protected void onPostExecute(String result) {  
            pdialog.dismiss();   
        }  

        @Override 
        protected void onPreExecute() {
        }  

        @Override 
        protected void onProgressUpdate(Integer... values) {   
        } 
     }  

DownloadDBTask task = new DownloadDBTask(context);  
task.execute("");