Persisting CheckBox Control State in GridTemplateColumn on Rebind

There are cases in which the user would like to retain the state for checkbox control inside GridTemplateColumn on grid operation which requires rebinding. In such situation you can use ViewState property on the page which holds the grid to save the current checkbox selection. The alteration of this property should be made in the OnCheckedChanged event handler of the respective checkbox.

The forthcoming sample presents how to retain the checkbox state in a hierarchical grid after expand/collapse for further custom operations. There are separate ViewState properties for each master/detail table. The example below is optimized for ViewState minimization as these properties are modified only when CheckBoxInstance.Checked is true. Otherwise the row value is not added to the ViewState.

Similar actions could be performed for persistence of other controls state in GridTemplateColumn.

ASP.NET

<telerik:RadGrid RenderMode="Lightweight" ID="RadGrid1" runat="server" AutoGenerateColumns="False" AllowSorting="True"
  AllowPaging="True" PageSize="3">
  <MasterTableView DataMember="Customers" PageSize="3" AllowPaging="True">
    <PagerStyle Mode="NumericPages"></PagerStyle>
    <Columns>
      ..............
      <telerik:GridBoundColumn UniqueName="CustomerID" ReadOnly="True" Display="False"
        DataField="CustomerID" />
      <telerik:GridTemplateColumn UniqueName="MasterTemplate" HeaderText="Checkbox column 1">
        <ItemTemplate>
          <asp:CheckBox ID="cbChecked" runat="server" AutoPostBack="True" OnCheckedChanged="CheckChanged">
          </asp:CheckBox>
        </ItemTemplate>
      </telerik:GridTemplateColumn>
      ..............
    </Columns>
    <DetailTables>
      <telerik:GridTableView DataMember="Customers1" PageSize="3" AllowPaging="True">
        <Columns>
          ...................
          <telerik:GridBoundColumn UniqueName="CustomerID" ReadOnly="True" Display="False"
            DataField="CustomerID" />
          <telerik:GridTemplateColumn UniqueName="Child1Template" HeaderText="Checkbox column 2">
            <ItemTemplate>
              <asp:CheckBox ID="cbChecked" runat="server" AutoPostBack="True" OnCheckedChanged="CheckChanged">
              </asp:CheckBox>
            </ItemTemplate>
          </telerik:GridTemplateColumn>
          ....................
        </Columns>
        <DetailTables>
          <telerik:GridTableView DataMember="Customers2" PageSize="3" AllowPaging="True">
            <Columns>
              .....................
              <telerik:GridBoundColumn UniqueName="CustomerID" ReadOnly="True" Display="False"
                DataField="CustomerID" />
              <telerik:GridTemplateColumn UniqueName="Child2Template" HeaderText="Checkbox column 3">
                <ItemTemplate>
                  <asp:CheckBox ID="cbChecked" runat="server" AutoPostBack="True" OnCheckedChanged="CheckChanged">
                  </asp:CheckBox>
                </ItemTemplate>
              </telerik:GridTemplateColumn>
              ......................
            </Columns>
          </telerik:GridTableView>
        </DetailTables>
      </telerik:GridTableView>
    </DetailTables>
  </MasterTableView>
</telerik:RadGrid>

C#

protected void CheckChanged(Object sender, System.EventArgs e)
{
    CheckBox box = (CheckBox)sender;
    GridDataItem item = (GridDataItem)box.NamingContainer;
    Hashtable target = null;

    if (item.OwnerTableView.DataMember == "Customers")
    {
        target = CustomersChecked;
    }
    else if (item.OwnerTableView.DataMember == "Customers1")
    {
        target = Customers1Checked;
    }
    else
    {
        target = Customers2Checked;
    }

    if (box.Checked)
    {
        target[item["CustomerID"].Text] = true;
    }
    else
    {
        target[item["CustomerID"].Text] = null;
    }
}

//. . .

private Hashtable CustomersChecked
{
    get
    {
        object res = ViewState["_cc"];
        if (res == null)
        {
            res = new Hashtable();
            ViewState["_cc"] = res;
        }

        return (Hashtable)res;
    }
}

private Hashtable Customers1Checked
{
    get
    {
        object res = ViewState["_cc1"];
        if (res == null)
        {
            res = new Hashtable();
            ViewState["_cc1"] = res;
        }

        return (Hashtable)res;
    }
}

private Hashtable Customers2Checked
{
    get
    {
        object res = ViewState["_cc2"];
        if (res == null)
        {
            res = new Hashtable();
            ViewState["_cc2"] = res;
        }

        return (Hashtable)res;
    }
}
private void RadGrid1_ItemDataBound(object sender, Telerik.Web.UI.GridItemEventArgs e)
{
    if (e.Item is GridDataItem)
    {
        GridDataItem item = e.Item as GridDataItem;
        CheckBox box = (CheckBox)item.FindControl("cbChecked");
        object isChecked = null;
        if (item.OwnerTableView.DataMember == "Customers")
        {
            isChecked = CustomersChecked[item["CustomerID"].Text];
        }
        if (item.OwnerTableView.DataMember == "Customers1")
        {
            isChecked = Customers1Checked[item["CustomerID"].Text];
        }
        if (item.OwnerTableView.DataMember == "Customers2")
        {
            isChecked = Customers2Checked[item["CustomerID"].Text];
        }
        if (isChecked != null)
        {
            box.Checked = (bool)isChecked == true;
        }
    }
}

VB

Private ReadOnly Property CustomersChecked As Hashtable
    Get
        Dim res As Object = ViewState("_cc")
        If (res Is Nothing) Then
            res = New Hashtable
            ViewState("_cc") = res
        End If
        Return CType(res, Hashtable)
    End Get
End Property

Private ReadOnly Property Customers1Checked As Hashtable
    Get
        Dim res As Object = ViewState("_cc1")
        If (res Is Nothing) Then
            res = New Hashtable
            ViewState("_cc1") = res
        End If
        Return CType(res, Hashtable)
    End Get
End Property

Private ReadOnly Property Customers2Checked As Hashtable
    Get
        Dim res As Object = ViewState("_cc2")
        If (res Is Nothing) Then
            res = New Hashtable
            ViewState("_cc2") = res
        End If
        Return CType(res, Hashtable)
    End Get
End Property

Protected Sub CheckChanged(ByVal sender As Object, ByVal e As System.EventArgs)
    Dim box As CheckBox = CType(sender, CheckBox)
    Dim item As GridDataItem = CType(box.NamingContainer, GridDataItem)
    Dim target As Hashtable = Nothing
    If (item.OwnerTableView.DataMember = "Customers") Then
        target = CustomersChecked
    ElseIf (item.OwnerTableView.DataMember = "Customers1") Then
        target = Customers1Checked
    Else
        target = Customers2Checked
    End If
    If box.Checked Then
        target(item("CustomerID").Text) = True
    Else
        target(item("CustomerID").Text) = Nothing
    End If
End Sub
Private Sub RadGrid1_ItemDataBound(ByVal sender As Object, ByVal e As Telerik.Web.UI.GridItemEventArgs) Handles RadGrid1.ItemDataBound

    If TypeOf e.Item Is GridDataItem Then
        Dim item As GridDataItem = CType(ConversionHelpers.AsWorkaround(e.Item, GetType(GridDataItem)), GridDataItem)
        Dim box As CheckBox = CType(item.FindControl("cbChecked"), CheckBox)
        Dim isChecked As Object = Nothing

        If item.OwnerTableView.DataMember = "Customers" Then
            isChecked = CustomersChecked(item("CustomerID").Text)
        End If
        If item.OwnerTableView.DataMember = "Customers1" Then
            isChecked = Customers1Checked(item("CustomerID").Text)
        End If
        If item.OwnerTableView.DataMember = "Customers2" Then
            isChecked = Customers2Checked(item("CustomerID").Text)
        End If

        If Not (isChecked Is Nothing) Then
            box.Checked = CType(isChecked, Boolean) = True
        End If

    End If
End Sub