第一次查询正常，第二次查询就会多查询数据一次，第三次再点击按钮查询的时候又会查询三次，奇怪了！那为给麻烦看看原因！！
private void btnQuery_Click(object sender, EventArgs e)
        {            
            dataG_rsj.Rows.Clear();           
            Bw.WorkerSupportsCancellation = true;
            Bw.WorkerReportsProgress = true;
            Bw.DoWork += new DoWorkEventHandler(Add);//绑定事件
            Bw.ProgressChanged += new ProgressChangedEventHandler(Progress);
            Bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(End);           
            Bw.RunWorkerAsync();

        }
 BackgroundWorker Bw = new BackgroundWorker();


        public void Add(object sender, DoWorkEventArgs e)
        {
           string strSql = "select  * from Sale_Table";
            OracleDataReader reader = App.DBE.ExecReader(strSql);
            object[] objcell = new object[34];
            if (reader.HasRows)
            {
                    while (reader.Read())
                    {
                        if ((Bw.CancellationPending == true))
                        {
                            e.Cancel = true;