DxComboBox<TData, TValue>.DataAsync Property

Specifies an asynchronous function that returns ComboBox data.

Namespace: DevExpress.Blazor

Assembly: DevExpress.Blazor.v23.1.dll

NuGet Package: DevExpress.Blazor

Declaration

[Parameter]
public Func<CancellationToken, Task<IEnumerable<TData>>> DataAsync { get; set; }

Property Value

Type	Description
Func<CancellationToken, Task<IEnumerable<TData>>>	A function that returns ComboBox data.

Remarks

Use the DataAsync property to bind the ComboBox to a strongly typed collection that is loaded asynchronously (for instance, from an HTTP request). This property allows you to prevent the page with the ComboBox from excessive re-rendering.

This property specifies an asynchronous function that returns a Task<IEnumerable<T>> object and accepts a CancellationToken object as a parameter. An exception occurs if you declare the function with an incorrect signature.

@using System.Threading;
@using System.Threading.Tasks;

<DxComboBox DataAsync="@GetDataAsync" @bind-Value="@Value"></DxComboBox>

@code {
    IEnumerable<string> Cities = new List<string>() {
        "London",
        "Berlin",
        "Paris",
    };

    string Value { get; set; }

    public Task<IEnumerable<string>> GetDataAsync(CancellationToken ct = default) {
        return Task.FromResult(Cities);
    }
}

If you bind the ComboBox to a data source that stores custom objects (IEnumerable<CustomType>), override the object’s Equals method and set the TextFieldName property. It specifies the custom object’s field name that returns strings to be shown in the ComboBox’s drop-down window.

Razor

@using BlazorApp.Data

<DxComboBox DataAsync="@Staff.GetDataAsync"
            @bind-Value="@SelectedPerson"
            TextFieldName="@nameof(Person.Text)"
            AllowUserInput="true">
</DxComboBox>

@code {
    Person SelectedPerson { get; set; } = Staff.DataSource[0];
}

Person

namespace BlazorApp.Data {
    public class Person {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public Department Department { get; set; }
        public string Text => $"{FirstName} {LastName} ({Department} Dept.)";
    }

    public enum Department { Motors, Electronics, Software }

    public override bool Equals(object obj) {
        if (obj is Person typedObj) {
            return (this.Id == typedObj.Id) && (this.FirstName == typedObj.FirstName) && (this.LastName == typedObj.LastName) 
            && (this.Department == typedObj.Department);
        }
        return base.Equals(obj);
    }
}

Staff

using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace BlazorApp.Data {
    public static class Staff {
        public static Task<IEnumerable<Person>> GetDataAsync(CancellationToken ct = default) {
            var dataSource = new List<Person>(){
                new Person() { Id= 0 , FirstName="John", LastName="Heart", Department=Department.Electronics },
                new Person() { Id= 1 , FirstName="Samantha", LastName="Bright", Department=Department.Motors },
                new Person() { Id= 2 , FirstName="Arthur", LastName="Miller", Department=Department.Software },
                new Person() { Id= 3 , FirstName="Robert", LastName="Reagan", Department=Department.Electronics },
                new Person() { Id= 4 , FirstName="Greta", LastName="Sims", Department=Department.Motors },
                new Person() { Id= 5 , FirstName="Brett", LastName="Wade", Department=Department.Software },
                new Person() { Id= 6 , FirstName="Sandra", LastName="Johnson", Department=Department.Electronics },
                new Person() { Id= 7 , FirstName="Edward", LastName="Holmes", Department=Department.Motors },
                new Person() { Id= 8 , FirstName="Barbara", LastName="Banks", Department=Department.Software },
                new Person() { Id= 9 , FirstName="Kevin", LastName="Carter", Department=Department.Electronics },
                new Person() { Id= 10, FirstName="Cynthia", LastName="Stanwick", Department=Department.Motors },
                new Person() { Id= 11, FirstName="Sam", LastName="Hill", Department=Department.Electronics }};
            return Task.FromResult(dataSource.AsEnumerable());
        }
    }
}

Otherwise, the ComboBox’s items are populated with CustomType.ToString() values.

Use the Data property if a strongly typed collection is loaded synchronously. Use the CustomData property if your data is stored on a remote service and is loaded through a Web API.