Is it possible to enable EnableVirtualScrolling for Combobox inside grid ?

[Joseph]

I have a large number of combobox   items inside a grid. The combobox display those
items to slow, so I tried to load Items on portions and after short search a found
what I was looking for. I found the example demo  ComboBox - Load on Demand Modes  . But I can’t figure it out how to do the same
thing inside a Grid?

[Shinu]

Hi Joseph,

Please have a look into the sample code snippet which works fine at my end.

ASPX:

<telerik:RadGrid ID="RadGrid1" runat="server" DataSourceID="SqlDataSource1" AutoGenerateColumns="false">
    <MasterTableView>
        <Columns>
            <telerik:GridBoundColumn DataField="OrderID" UniqueName="OrderID">
            </telerik:GridBoundColumn>
            <telerik:GridBoundColumn DataField="CustomerID" UniqueName="CustomerID">
            </telerik:GridBoundColumn>
            <telerik:GridTemplateColumn>
                <ItemTemplate>
                    <telerik:RadComboBox ID="RadComboBox2" runat="server" Width="250" Height="150" EmptyMessage="Select a Company"  EnableLoadOnDemand="True" ShowMoreResultsBox="true" EnableVirtualScrolling="true" OnItemsRequested="RadComboBox2_ItemsRequested">
                    </telerik:RadComboBox>
                    </EditItemTemplate>
                </ItemTemplate>
            </telerik:GridTemplateColumn>
        </Columns>
    </MasterTableView>
</telerik:RadGrid>

C#:

private const int ItemsPerRequest = 10;
protected void RadComboBox2_ItemsRequested(object sender, RadComboBoxItemsRequestedEventArgs e)
{
    RadComboBox combo = (RadComboBox)sender;
    DataTable data = GetData(e.Text);
    int itemOffset = e.NumberOfItems;
    int endOffset = Math.Min(itemOffset + ItemsPerRequest, data.Rows.Count);
    e.EndOfItems = endOffset == data.Rows.Count;
    for (int i = itemOffset; i < endOffset; i++)
    {
        combo.Items.Add(new RadComboBoxItem(data.Rows[i]["CompanyName"].ToString(), data.Rows[i]["CompanyName"].ToString()));
    }
}
private static DataTable GetData(string text)
{
    SqlDataAdapter adapter = new SqlDataAdapter("SELECT * from Customers WHERE CompanyName LIKE @text + '%'",ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
    adapter.SelectCommand.Parameters.AddWithValue("@text", text);
    DataTable data = new DataTable();
    adapter.Fill(data);
    return data;
}

Thanks,
Shinu.

[Joseph]

Hi Shinu
Thank you for your quick answer. The example works fine, but still when I scroll down, the combox triggers the  OnItemsRequested even when all items are loaded.
So the next question is how to stop from OnItemsRequested  from firing when all items are loaded?


 

[Shinu]

Hi Joseph,

In this scenario the RadComboBox is not loading all the items initially. It will load only first 10 items initially because here the ItemsPerRequest is set it as 10. So when you are scrolling it will load next 10 items. This is the way of working ItemsRequestedevent. As a suggestion you can do the following modification in your ItemsRequested event to achieve your scenario.

C#:

protected void RadComboBox2_ItemsRequested(object sender, RadComboBoxItemsRequestedEventArgs e)
{
    RadComboBox combo = (RadComboBox)sender;
    DataTable data = GetData(e.Text);
    for (int i = 0; i < data.Rows.Count; i++)
    {
        combo.Items.Add(new RadComboBoxItem(data.Rows[i]["CompanyName"].ToString(), data.Rows[i]["CompanyName"].ToString()));
    }
}

Thanks,
Shinu.

[Joseph]

Thanks Shinu. It is working fine :)