WebUserControl - DataItem null for ListBox when using ObjectDataSource

[AdventurGurl]

When using RadGrid's WebUserControl, the DataItem object becomes null when using an ObjectDataSource only to fill ListBox.

Scenario 1 Works - Calling DataSource = __ and DataBind() in Page_Load:

protected void Page_Load(object sender, EventArgs e)
{
    lstItemCollection.DataSource = GetCityCollection();
    lstItemCollection.DataBind();
}
public IEnumerable<Customer> GetCityCollection()
{
    using (UowEntities uow = new UowEntities())
    {
        CustomerRepository cr = new CustomerRepository(uow);
        return cr.SelectAll().ToArray();
    }
}

<asp:ListBox ID="lstItemCollection" runat="server" SelectionMode="Multiple" 
    DataValueField="CustomerId" DataTextField="City"  />

Scenario 2 - DataItem object is null when needed if using ObjectDataSource to bind data to ListBox:

<asp:ListBox ID="lstItemCollection" runat="server" SelectionMode="Multiple" DataValueField="CustomerId" DataTextField="City" DataSourceID="odsCityCollection" />
<asp:ObjectDataSource ID="odsCityCollection" runat="server" SelectMethod="GetCityCollection"
TypeName="LINQScratchPad.Web.CommonUserControls.CustomerControl" ></asp:ObjectDataSource>

The ObjectDataSource automatically calls the GetCityCollection() method and that is when the DataItem becomes null. Later in the page lifecycle it will have a value again until I force the ListBox to DataBind in attempt to see if I have a value to DataItem (or even access to a HiddenField for that matter!).  I want the CustomerId value to filter my query in the SelectMethod of the ObjectDataSource. **NOTE: this is a very simple example and not real-world as I have moved to a play project for testing to resolve the underlying issue of a null DataItem.** I added the PreRender event handlers to show I have access to the DataItem again after it had become null.

public partial class CustomerControl : System.Web.UI.UserControl

{

    private object _dataItem;

    public object DataItem

    {

        get { return this._dataItem; }

        set { this._dataItem = value; }

    } 

    protected void Page_Load(object sender, EventArgs e)  {  }



    public IEnumerable<Customer> GetCityCollection()

    {

        using (UowEntities uow = new UowEntities())

        {

            Customer foo = (Customer)DataItem; // Always null!

              

            // Will throw null reference exception here if uncommented

            //var bar = HiddenField1.Value; 

            CustomerRepository cr = new CustomerRepository(uow);

            return cr.SelectAll().ToArray();

        }

    }

      

    protected void Page_PreRender(object sender, EventArgs e)

    {

        Customer foo = (Customer)DataItem; // Has value here

        var bar = this.HiddenField1.Value; // Has value here

        lstItemCollection.DataBind(); // DataItem is now null again :(

    }

    protected override void OnPreRender(EventArgs e)

    {

        Customer foo = (Customer)DataItem; // Has value here

        var bar = this.HiddenField1.Value; // Has value here

        lstItemCollection.DataBind(); // DataItem is now null again :(

        base.OnPreRender(e);

    }

}

In watching the DataItem value throughout the page lifecycle process, this is what I observed:
Page_Load - DataItem has value.  {F10}
Sets my HiddenField value. {F10}

<asp:HiddenField Value='<%# Eval("CustomerId") %>'  ID="HiddenField1" runat="server" />

Sets my other two Binds. {F10}

<ol class="column1">
    <li>
        <asp:Label ID="lblFirstName" runat="server">First Name:</asp:Label>
        <asp:TextBox ID="txtFirstName" runat="server"  Text='<%# Bind("FirstName") %>' />
    </li>
    <li>
        <asp:Label ID="lblLastName" runat="server">Last Name: </asp:Label>
        <asp:TextBox ID="txtLastName" runat="server" Text='<%# Bind("LastName") %>' />
    </li>
</ol>

ObjectDataSource calls GetCityCollection() and now DataItem object is null.

After that when stepping into the PreRender the DataItem has a value again until calling ListBox.DataBind() where the ObjectDataSource steps into the GetCityCollection() method and DataItem is once again null.

Can anybody explain why DataItem becomes null please?  
Thanks in advance!!
-Carrie

[Iana Tsolova]

Hi AdventurGurl,

The DataItem object for a grid item is available during it is bound. Therefore I suggest that you handle the user control DataBinding event to bind the ListBox. Check the below demo for a reference:
http://demos.telerik.com/aspnet-ajax/grid/examples/dataediting/usercontroleditform/defaultcs.aspx

Best wishes,
Iana
the Telerik team