Use SfDataManager to populate the grid.
        <SfGrid TValue="OrderItem">
            <SfDataManager Url="https://www.mydomain.com/api/orderitemwithcount/1002" Adaptor="Adaptors.WebApiAdaptor"></SfDataManager>
            <GridColumns>
                <GridColumn Field=@nameof(OrderItem.OrderId) HeaderText="Order Id"></GridColumn>
                <GridColumn Field=@nameof(OrderItem.ProductCode) HeaderText="Code"></GridColumn>
                <GridColumn Field=@nameof(OrderItem.ProductName) HeaderText="Name"></GridColumn>
                <GridColumn Field=@nameof(OrderItem.ProductSku) HeaderText="Sku"></GridColumn>
            </GridColumns>
        </SfGrid>Note: The result xml/json must contain Items and Count properties.
    public class OrderItemWithCount
    {
        public List<DCOrderItem> Items { get; set; }
        public int Count   
        {
            get => Items.Count;
        }
    }        public OrderItemWithCount Get(int id)
        {
            WSOrderClient wsOrder = new WSOrderClient("BasicHttpsBinding_IWSOrder");
            OrderItemWithCount result = new OrderItemWithCount();
            result.Items = wsOrder.GetOrderItemList(id);
            wsOrder.Close();
            return result;
        }
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