ASP.NET MVC ComboBox - Load Items On Demand with Paging


The items of the ComboBox can be loaded on-demand (via AJAX requests). The advantage of using this approach is that the items are loaded only when the end user types something into the input field. Thus, the page will load very fast because no item is loaded on page load.

In order to enable the on demand loading feature, set the EnableLoadOnDemand property to true. You also need to specify an action method that will be used to load the items on demand, using the OnLoadingItems property. This action method will load all the items that match the text typed in the input field.

To improve the performance even further, you can use the "paging" approach for the load on demand feature. Using this approach will force the ComboBox to load only a limited number at a time, instead of retrieving all the matches at once. So for example, if there are 10,000 items in the database, you can configure the ComboBox to load 100 items at a time, to make the on demand loading functionality run smoother.

To load the next set of items, the end user simply needs to click on the footer text from the bottom of the list with items.
View - Aspx
 
    <% Html.Obout(new ComboBox("ComboBox1") 
    {                
        EnableLoadOnDemand = true,
        OnLoadingItems = "ComboBox/LoadingItemsWithPaging"
    }); %>
    
View - Razor
 
    @Html.Obout(new ComboBox("ComboBox1") 
    {                
        EnableLoadOnDemand = true,
        OnLoadingItems = "ComboBox/LoadingItemsWithPaging"
    })
    
Controller
   
    public JsonResult LoadingItemsWithPaging(ComboBoxLoadingItemsEventArgs args)
    {
        ComboBoxItemList items = GetFilteredCustomers(args.Text, args.ItemsOffset);
        int itemsCount = GetFilteredCustomersCount(args.Text);
        int itemsLoadedCount = args.ItemsOffset + items.Count();

        JsonResult result = new JsonResult
        {
            Data = new
            {
                Items = items,
                ItemsCount = itemsCount,
                ItemsLoadedCount = itemsLoadedCount
            },
            JsonRequestBehavior = JsonRequestBehavior.AllowGet
        };

        return result;
    }
    
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