我想我的GridView的第一页上选择一个复选框，并选择在另一个我的GridView2页

你好，我想我通过我的GridView GridView和页的第一页上的复选框取消选中我，我在第一页中选择的复选框来选择。下面是代码，我用，但我得到一个错误，说:"错误:Sys.WebForms.PageRequestManagerServerErrorException:未将对象引用设置到对象的实例。"有人可以帮助，请

 

        private void RememberOld()

        {

            ArrayList candidateID = new ArrayList();

            int index = -1;

            foreach (GridViewRow row in GridView3.Rows)

            {

                index = int.Parse(GridView3.DataKeys[row.RowIndex].Value.ToString());

                bool result = ((CheckBox)row.FindControl("chkselect")).Checked;

                if (Session["CHECKED_ITEMS"] != null)

                    candidateID = (ArrayList)Session["CHECKED_ITEMS"];

                if (result)

                {

                    if (!candidateID.Contains(index))

                        candidateID.Add(index);

                }

                else

                    candidateID.Remove(index);

                

            }

            if (candidateID != null && candidateID.Count > 0)

                Session["CHECKED_ITEMS"] = candidateID;

        }

        private void RepopulateValues()

        {

            ArrayList candidateID = (ArrayList)Session["CHECKED_ITEMS"];

            if (candidateID != null && candidateID.Count > 0)

            {

                foreach (GridViewRow row in GridView3.Rows)

                {

                    int index = int.Parse(GridView3.DataKeys[row.RowIndex].Value.ToString());

                    CheckBox mycheckbox = (CheckBox)row.FindControl("chkselect");

                    if (candidateID.Contains(index))

                    {

                        mycheckbox.Checked = true;

                    }

 

                    else

                        mycheckbox.Checked = false;

                }

            }

        }

 

   

        protected void GridView3_PageIndexChanging(object sender, GridViewPageEventArgs e)

        {

            RememberOld();

            GridView3.PageIndex = e.NewPageIndex;

            GridView3.DataBind(); // Your logic to bind gridview

            RePopulateValues();

        }