为什么我在DELPHI中用WaitForSingleObject时整个窗体都死了?

我想用waitForSingleObject来监听目录中是不是有新文件,可是在WHILE循环中总是使整个窗体都死了???程序如下:procedure TForm1.jt(Sender: TObject);
var  NotificationHandle:THandle;
     waiting:boolean;
     dwResult: DWORD;
begin
     NotificationHandle:=FindFirstChangeNotification(PChar(filebox.Directory), FALSE,FILE_NOTIFY_CHANGE_FILE_NAME);
     if (NotificationHandle <> INVALID_HANDLE_VALUE) then
     statusbar1.Panels[1].Text:='现在正在监听目录'
     else
        begin
          showmessage('目录监听出错!');
          exit;
        end;
     waiting:=true;
     Application.ProcessMessages;
     while waiting do
     begin
         dwResult := WaitForSingleObject(NotificationHandle,INFINITE);
         waiting:=false;
         {if (dwResult=WAIT_OBJECT_0) then
             begin
                showmessage('目录中的新文件进入了!');
                statusbar1.Panels[1].Text:='有新文件';
                if Application.MessageBox('你想继续监听目录吗?', 'Continue?', MB_ICONQUESTION or MB_YESNO)=IDYES then
                    FindNextChangeNotification(NotificationHandle)
                else
                    begin
                      statusbar1.Panels[1].Text:='目录监听取消';
                      waiting:=false;
                    end;
             end;   }
     end;
     FindCloseChangeNotification(NotificationHandle);end;
  如果用directorlistbox的COUNT属性来检测时,也是同样的问题..???????