How to maintain state and count of checkbox of gridview paging in ASP.NET C#

<asp:GridView ID="gvAppvrDetail" runat="server" AutoGenerateColumns="False"
      AllowPaging="true" PageSize="10"  Width="1000PX"
      onpageindexchanging="gvAppvrDetail_PageIndexChanging"
      onrowdatabound="gvAppvrDetail_RowDataBound"  >
      <Columns>
        <asp:TemplateField>
         <HeaderTemplate>
         <asp:CheckBox ID="ChkAll" runat="server" onclick="javascript:SelectAllCheckboxes(this);" >
         </asp:CheckBox>
        </HeaderTemplate>
        <ItemTemplate>
        <asp:CheckBox ID="ChkChild" runat="server"  onclick="CheckBoxCount();"   OnCheckedChanged="ChkChild_CheckedChanged" >
            </asp:CheckBox>
        </ItemTemplate>
        </asp:TemplateField>

</Columns>

</asp:GridView>

gvAppvrDetail_PageIndexChanging

protected void gvAppvrDetail_PageIndexChanging(object sender, GridViewPageEventArgs e)
       {
           gvAppvrDetail.PageIndex = e.NewPageIndex;
           BindGridview(Request.QueryString["PREFIX"].ToString());

           //Code to maintain selected record while paging

           if (ViewState["SelectedRows"] != null)
           {
               List<string> selectedItems = (List<string>)ViewState["SelectedRows"];
               foreach (GridViewRow row in gvAppvrDetail.Rows)
               {

                   Label lblEntryNo = (Label)row.FindControl("lblEntryNo");

                   var result = selectedItems.Find(item => item == lblEntryNo.Text);
                   if (result != null)
                   {
                       CheckBox chk = (CheckBox)row.FindControl("ChkChild");
                       if (chk != null)
                       {
                            chk.Checked = true;
                            ViewState["Count"] = Convert.ToInt32(ViewState["Count"]) + 1;
                            lblcntRows.Text = ViewState["Count"].ToString();
                       }
                   }
               }
           }
           //BindGridview(Request.QueryString["PREFIX"].ToString());
       }

ChkChild_CheckedChanged

protected void ChkChild_CheckedChanged(object sender, EventArgs e)
      {
          CheckBox chkStatus = (CheckBox)sender;
          GridViewRow selectedrow = (GridViewRow)chkStatus.NamingContainer;

          //Getting selected records from View state
          List<string> selectedItems = null;

          if (ViewState["SelectedRows"] != null)
          {
              selectedItems = (List<string>)ViewState["SelectedRows"];
          }
          else
          {
              selectedItems = new List<string>();
          }

          Label lblEntryNo = (Label)selectedrow.FindControl("lblEntryNo");


          if (chkStatus.Checked)
          {
             selectedItems.Add(lblEntryNo.Text);

          }
          else
           {
              var result = selectedItems.Find(item => item == lblEntryNo.Text);

              if (result != null)
              {
                  selectedItems.Remove(lblEntryNo.Text);
              }
          }

          //Assigning Selected records to ViewState
          ViewState["SelectedRows"] = selectedItems;
      }