为什么判断为'


    protected void But_ok_Click(object sender, EventArgs e)
    {
        string list =Request.Form["chk_list"];
        string checkdata = tex_checkDate.Text.Trim();
        if (list != "" && checkdata !="")
       {
           SqlConnection con = new SqlConnection(conString);
           SqlCommand cmd = new SqlCommand();
           cmd.Connection = con;
           cmd.CommandText = "update GGPRODUCT set isChecked=1, checkedName='改名字', checkedDate=@checkedDate where ID in (" + list + ")";
           cmd.Parameters.AddWithValue("@checkedDate", Convert.ToDateTime(checkdata));
           using (con)
           {
               con.Open();
               int queryResult = cmd.ExecuteNonQuery();
               if (queryResult != 0)
               {
                   Response.Write("<script language=javascript>alert('验收成功');location.href='productMakeList.aspx'; </script>");
               }
               else
               {
                   Response.Write("<script language=javascript>alert('操作失败'); </script>");
               }
           }
       }
       else
       {
           Response.Write("<script language=javascript>alert('请先选择和输入时间'); </script>");
       }
    }