Virtualization in AutoComplete Component

8 Jul 202410 minutes to read

AutoComplete virtualization is a technique used to efficiently render extensive lists of items while minimizing the impact on performance. This method is particularly advantageous when dealing with large datasets because it ensures that only a fixed number of DOM (Document Object Model) elements are created. When scrolling through the list, existing DOM elements are reused to display relevant data instead of generating new elements for each item. This recycling process is managed internally.

During virtual scrolling, the data retrieved from the data source depends on the popup height and the calculation of the list item height. Enabling the enableVirtualization option in a AutoComplete activates this virtualization technique.

When fetching data from the data source, the actionBegin event is triggered before data retrieval begins. Then, the actionComplete event is triggered once the data is successfully fetched.

When the enableVirtualization property is enabled, the skip and take properties provided by the user within the Query class at the initial state or during the actionBegin or actionComplete events will not be considered, since it is internally managed and calculated based on certain dimensions with respect to the popup height.

Binding local data

The AutoComplete can generate its list items through an array of complex data. For this, the appropriate columns should be mapped to the fields property. When using virtual scrolling, the list updates based on the scroll offset value, triggering a request to fetch more data from the server. As the data is being fetched, the actionBegin event occurs before the data retrieval starts. Once the data retrieval is successful, the actionComplete event is triggered, indicating that the data fetch process is complete.

In the following example, text column from complex data have been mapped to the value field.

@{
    var data = new RecordData().RecordModelList();
}

<div class="control-wrapper">
    <div id="default" style='padding-top:75px;margin:0 auto;width:250px;'>
        <ejs-autocomplete id="records" dataSource="@data" placeholder="e.g. Item 1" allowFiltering="true" enableVirtualization="true" popupheight="200px">
            <e-autocomplete-fields value="Text" ></e-autocomplete-fields>
        </ejs-autocomplete>
    </div>
</div>
...
public class RecordData
{
    public string ID { get; set; }
    public string Text { get; set; }
    public List<RecordData> RecordList { set; get; }
    public List<RecordData> RecordModelList()
    {
        return Enumerable.Range(1, 150).Select(i => new RecordData()
        {
            ID = i.ToString(),
            Text = "Item " + i,
        }).ToList();
    }
}

Binding remote data

The AutoComplete supports the retrieval of data from remote data services with the help of the DataManager component, triggering the actionBegin and actionComplete events, and then updating the list data. During virtual scrolling, additional data is retrieved from the server, triggering the actionBegin and actionComplete events at that time as well.

The following sample displays the OrderId from the Orders Data Service.

@{
    var data = new BindingRecord().RecordModelList();
}

<div class="control-wrapper">
    <div id="default" style='padding-top:75px;margin:0 auto;width:250px;'>
        <ejs-autocomplete id="records" dataSource="@data" placeholder="e.g. Item 1" allowFiltering="true" enableVirtualization="true" popupheight="200px">
            <e-data-manager adaptor="WebApiAdaptor" url="https://services.syncfusion.com/aspnet/production/api/Orders" crossDomain="true"></e-data-manager>
            <e-autocomplete-fields  value="OrderID" ></e-autocomplete-fields>
        </ejs-autocomplete>
    </div>
</div>
...
public class BindingRecord
{
    public string ID { get; set; }
    public string Text { get; set; }
    public List<BindingRecord> RecordList { set; get; }
    public List<BindingRecord> RecordModelList()
    {
        return Enumerable.Range(1, 150).Select(i => new BindingRecord()
        {
            ID = i.ToString(),
            Text = "Item " + i,
        }).ToList();
    }
}

Customizing items count in virtualization

When the enableVirtualization property is enabled, the take property provided by the user within the Query parameter at the initial state or during the actionBegin event will be considered. Internally, it calculates the items that fit onto the current page (i.e., probably twice the amount of the popup’s height). If the user-provided take value is less than the minimum number of items that fit into the popup, the user-provided take value will not be considered.

The following sample shows the example for Customizing items count in virtualization.

<div class="control-wrapper">
    <div id="default" style='padding-top:75px;'>
        <ejs-autocomplete id="records" dataSource="@ViewBag.data" query="new ej.data.Query().take(40)" actionBegin="onbegin" placeholder="Select a item" allowFiltering="false" enableVirtualization="true" popupHeight="200px">
            <e-autocomplete-fields value="Text"></e-autocomplete-fields>
        </ejs-autocomplete>
    </div>
</div>

<script>
    function onbegin(e) {
        e.query = new ej.data.Query().take(45);
    }
</script>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using WebApplication1.Models;

namespace WebApplication1.Controllers
{
    public class MultiSelectController : Controller
    {
        public ActionResult virtualscroll()
        {
            ViewBag.data = new Record().RecordModelList();
            return View();
        }
    }
}

Grouping

The AutoComplete component supports grouping with Virtualization. It allows you to organize elements into groups based on different categories. Each item in the list can be classified using the groupBy field in the data table. After grouping, virtualization works similarly to local data binding, providing a seamless user experience. When the data source is bound to remote data, an initial request is made to retrieve all data for the purpose of grouping. Subsequently, the grouped data works in the same way as local data binding virtualization, enhancing performance and responsiveness.

The following sample shows the example for Grouping with Virtualization.

@{
    var data = new GroupingRecord().RecordModelList();
}

<div class="control-wrapper">
    <div id="default" style='padding-top:75px;margin:0 auto;width:250px;'>
        <ejs-autocomplete id="records" dataSource="@data" placeholder="e.g. Item 1" allowFiltering="true" enableVirtualization="true" popupheight="200px">
            <e-autocomplete-fields groupBy="Group" value="Text" ></e-autocomplete-fields>
        </ejs-autocomplete>
    </div>
</div>
...
public class GroupingRecord
{
    public string ID { get; set; }
    public string Text { get; set; }
    public string Group { get; set; }
    public List<GroupingRecord> RecordList { set; get; }
    public List<GroupingRecord> RecordModelList()
    {
        Random random = new Random();
        return Enumerable.Range(1, 150).Select(i => new GroupingRecord()
        {
            ID = i.ToString(),
            Text = "Item " + i,
            Group = GetRandomGroup(random),

        }).ToList();
    }
    public string GetRandomGroup(Random random)
    {
        // Generate a random number between 1 and 4 to determine the group
        int randomGroup = random.Next(1, 5);
        switch (randomGroup)
        {
            case 1:
                return "Group A";
            case 2:
                return "Group B";
            case 3:
                return "Group C";
            case 4:
                return "Group D";
            default:
                return string.Empty;
        }
    }
}