Virtualization in Blazor ComboBox Component

14 Mar 20245 minutes to read

The ComboBox component includes a virtual scrolling feature designed to enhance UI performance, particularly for handling large datasets. By enabling the EnableVirtualization option, the ComboBox intelligently manages data rendering, ensuring only a subset of items is initially loaded when the component is rendered. As you interact with the dropdown, additional items are dynamically loaded as you scroll, creating a smooth and efficient user experience.

This feature is applicable to both local and remote data scenarios, providing flexibility in its implementation. For instance, consider a case where the ComboBox is bound to a dataset containing 150 items. Upon opening the dropdown, only a few items are loaded initially, based on the height of the popup. As you scroll through the list, additional items are fetched and loaded on-demand, allowing you to effortlessly explore the complete dataset.

@using Syncfusion.Blazor.DropDowns
@using Syncfusion.Blazor.Data

<SfComboBox TValue="string" TItem="Record" Placeholder="Select an item" DataSource="@Records" Query="@LocalDataQuery" PopupHeight="130px" EnableVirtualization="true">
    <ComboBoxFieldSettings Text="Text" Value="ID"></ComboBoxFieldSettings>
</SfComboBox>

@code{
    public Query LocalDataQuery = new Query().Take(6); 
    public class Record 
    { 
        public string ID { get; set; } 
        public string Text { get; set; } 
    } 
    public List<Record> Records { get; set; } 
    protected override void OnInitialized()
    { 
        this.Records = Enumerable.Range(1, 150).Select(i => new Record() 
        { 
            ID = i.ToString(), 
            Text = "Item " + i, 
        }).ToList(); 
    } 
}

Grouping with Virtualization

The Combobox 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.

@using Syncfusion.Blazor.DropDowns
@using Syncfusion.Blazor.Data

<SfComboBox TValue="string" TItem="Record" Placeholder="e.g. Item 1" DataSource="@Records" Query="@LocalDataQuery" PopupHeight="130px" EnableVirtualization="true">
    <ComboBoxFieldSettings Text="Text" Value="ID" GroupBy="Group" />
</SfComboBox>

@code{
    public Query LocalDataQuery = new Query().Take(6); 
    public class Record
    {
        public string ID { get; set; }
        public string Text { get; set; }
        public string Group { get; set; }
    }
    public List<Record> Records { get; set; } 
    protected override void OnInitialized()
    {
        var random = new Random();
        this.Records = Enumerable.Range(1, 150).Select(i => new Record()
            {
                ID = i.ToString(),
                Text = "Item " + i,
                Group = GetRandomGroup(random)
            }).ToList();
    }
    private string GetRandomGroup(Random random)
    {
        switch (random.Next(1, 5))
        {
            case 1:
                return "Group A";
            case 2:
                return "Group B";
            case 3:
                return "Group C";
            case 4:
                return "Group D";
            default:
                return string.Empty;
        }
    }
}

Keyboard interaction

Users can navigate through the scrollable content using keyboard keys. This feature loads the next or next set of items based on the key inputs in the popup.The ComboBox supports the following keyboard shortcuts.

Key	Action
ArrowDown	Loads the next virtual list item if the selection is present in last item of the current page.
ArrowUp	Loads the previous virtual list item if the selection is present in first item of the current page.
PageDown	Loads the next page and selects the last item in it.
PageUp	Loads the previous page and selects the first item in it.