multi checkbox in radcombbox and get select checkbox Result to gridview

1. 
pls i need Answer this question by vb code language pls what can i change in this code to fix my proplem

 I have 2 controls radcombobox and gridview
2.  Radcombobox databind
Private con As New SqlConnection("Data Source=bma-pc;Initial Catalog=hrdb;Integrated Security=True")


    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        '   RadComboBoxEmp1_ID.AutoPostBack = True


        Dim adapter As New SqlDataAdapter("SELECT   EMPL_ID, EMPL_ID+' '+FIRST_NAME+' '+ISNULL(SECOND_NAME,' ')+' '+ ISNULL(FAMILY_NAME,' ') as EMPL_NAME FROM  HAL_HR_EMPLOYE_BSC_TAP where  END_SERVC_FLG   LIKE  '0' OR  END_SERVC_FLG  IS NULL  order by cast([EMPL_ID]as int) asc ", con)
        Dim links As New DataTable()
        adapter.Fill(links)

        RadComboBoxEmp1_ID.DataTextField = "EMPL_NAME"
        RadComboBoxEmp1_ID.DataValueField = "EMPL_ID"
        RadComboBoxEmp1_ID.DataSource = links
        RadComboBoxEmp1_ID.DataBind()

   End Sub


3.  Radcombobox I don’t have properties  EnableCheckAllItemsCheckBox="true" I create 2 checkbox control in radcombobox template

a.  <HeaderTemplate>

<asp:CheckBox ID="CheckBox2" runat="server" Text="ALL" AutoPostBack="True"
oncheckedchanged="CheckBox2_CheckedChanged" />
</HeaderTemplate>
b.  <ItemTemplate>
 <asp:CheckBox ID="CheckBox1" runat="server" AutoPostBack="True"
                  AutoPostBack="True"
oncheckedchanged="CheckBox2_CheckedChanged"
Text='<%# Eval("EMPL_NAME") %>' />
</ItemTemplate>
c.  Behind code
  Protected Sub CheckBox2_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs)

        Dim chk As CheckBox = TryCast(sender, CheckBox)

        If chk.ID = "CheckBox2" Then
            For Each item As RadComboBoxItem In RadComboBoxEmp1_ID.Items
                '  If item..RowType = DataControlRowType.DataRow Then

                item.Controls.OfType(Of CheckBox)().FirstOrDefault().Checked = chk.Checked

                ' row.Cells(2).Controls.OfType(Of RadComboBox)().FirstOrDefault().Visible = False
                '   End If
                TextBox1.Text += "'" & item.Value & "',"


            Next



        End If

        For Each item As RadComboBoxItem In RadComboBoxEmp1_ID.Items

            DirectCast(item.FindControl("CheckBox1"), CheckBox).Checked = chk.Checked
            If DirectCast(item.FindControl("CheckBox1"), CheckBox).ID <> "CheckBox1" Then
                chk.Checked = False
            End If
            '  chk.Checked = False
            ' Dim chk As CheckBox = TryCast(sender, CheckBox)
            ' If chk.Checked = True Then
            TextBox2.Text += DirectCast(item.FindControl("CheckBox1"), CheckBox).ID & ", "
            'End If
            If DirectCast(item.FindControl("CheckBox1"), CheckBox).Checked = True Then
                DirectCast(item.FindControl("CheckBox1"), CheckBox).Checked = True
                TextBox2.Text += DirectCast(item.FindControl("CheckBox1"), CheckBox).ID & ", "
            End If



        Next

        RadComboBoxEmp1_ID.OpenDropDownOnLoad = True

    End Sub




When I dropdownopen radcombobox show select check  all object with checkbox CheckBox2 name  and when I change the checkbox all it select check  all object  and remove all select check  when I remove
In ItemTemplate but my problem start when I change  checkbox in <ItemTemplate>  <asp:CheckBox ID="CheckBox1" here when I select item with select check 1 by 1 or remove some select check not work I need help to change select check

4.  Gridview I need after select check  in radcombobox but the value in
Private Sub BindGrid()
Dim cmd As New SqlCommand("SELECT   EMPL_ID, EMPL_ID+' '+FIRST_NAME+' '+ISNULL(SECOND_NAME,' ')+' '+ ISNULL(FAMILY_NAME,' ') as EMPL_NAME FROM  HAL_HR_EMPLOYE_BSC_TAP where here after select check how I but the value from radcombobox  ")
GridViewEmpl.DataSource = Me.ExecuteQuery(cmd, "SELECT")
GridViewEmpl.DataBind()

to get data in the gridview filtering or find item by radcombobox or create parameter to get select check pls help me what to do