ProgressDialog不显示有关问题

//开始线程读取数据方法      public void startLoadData()       {          pBar = ProgressDialog.show(this, "请稍后...", "检测查询信息中...", true,  false);           Thread GetData = new Thread(new Getdata());             GetData.start();         }          public class Getdata implements Runnable {                     public void run() {                         loadData();                      messageListener.sendEmptyMessage(TASK_LOOP_COMPLETE);                     }                                      }               private Handler messageListener = new Handler()      {                public void handleMessage(Message msg)              {                     switch(msg.arg1)                  {                     case TASK_LOOP_COMPLETE:                         pBar.dismiss();                         //数据读取完成，关闭线程并加载数据                      SetData();                      break;                                              }                 }         };