DxComboBox<TData, TValue> Class

A text box editor with an integrated multi-column dropdown list that supports item filtering and virtual scrolling.

Namespace: DevExpress.Blazor

Assembly: DevExpress.Blazor.v23.2.dll

NuGet Package: DevExpress.Blazor

Declaration

public class DxComboBox<TData, TValue> :
    DxComboBoxBase<TData, TValue>,
    IFilteringComponent,
    IRequireSelfCascading,
    IDataSourceSettings<TData>,
    IServiceProviderAccessor,
    IEditorSettingsAccessor,
    IFocusableEditor,
    IDropDownOwner

Type Parameters

Name	Description
TData	The data item type.
TValue	The value type.

Remarks

The DevExpress ComboBox for Blazor (<DxComboBox>) component displays a drop-down window with a list of items. Users can click an item in the drop-down list or use the Up arrow, Down arrow, and Enter keys to navigate between items and select them. When a user presses and holds an arrow key, the editor’s window continuously navigates between items.

Run Demo Watch Video

Add a ComboBox to a Project

Follow the steps below to add the ComboBox component to an application:

1. Use a DevExpress Project Template to create a new Blazor Server or Blazor WebAssembly application. If you use a Microsoft project template or already have a Blazor project, configure your project to incorporate DevExpress Blazor components.
2. Add the <DxComboBox>…</DxComboBox> markup to a .razor file.
3. Bind the component to data.
4. Configure the component: add a clear button and placeholder, customize appearance, specify the filter mode, and so on (see the sections below).

Bind to Data

Strongly Typed Collection

Use the Data property to bind the ComboBox to a strongly typed collection or enumeration. Initialize this object in the OnInitialized lifecycle method or before this method is invoked. Use the DataAsync property instead of the Data property if a strongly typed collection is loaded asynchronously (for instance, from an HTTP request).

View Example: ComboBox for Blazor - Bind to an enumeration

Use the Value property to specify the component’s selected value or item. You can use the @bind attribute to bind the Value property to a data field. For more information, refer to the following help topic: Two-Way Data Binding.

<DxComboBox Data="@Cities" @bind-Value="@Value" ></DxComboBox>

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

  string Value { get; set; }
}

The ComboBox can detect IQueryable<T> collections and use benefits of the corresponding LINQ query providers (such as Entity Framework).

Custom Object Collection

You can bind the ComboBox to a data collection (Data) that stores custom objects (IEnumerable<CustomType>). The Value property can also contain a custom object. In this case, you need to override the custom object’s Equals method. Otherwise, the ComboBox uses the default Equals method implementation to compare items in the Data collection and the Value item. This method determines whether two object instances are equal. The compared items will not be equal if they are different instances (even if they have exactly the same properties). As a result, the component will not display a selected item.

You also need to set the TextFieldName property. It specifies the custom object’s field name that returns strings to be shown in the ComboBox drop-down window. If the TextFieldName property is not specified, the ComboBox component searches for a Text field in the data source and uses this field as a text field. Otherwise, the ComboBox is populated with CustomType.ToString() values.

Razor

@using BlazorApp.Data

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

@code {
  Person Value { 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;
using System.Collections.Generic;

namespace BlazorApp.Data {
    public static class Staff {
        private static readonly Lazy<List<Person>> dataSource = new Lazy<List<Person>>(() => {
            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 dataSource;
        });
        public static List<Person> DataSource { get { return dataSource.Value; } }
    }
}

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

Run Demo: ComboBox - Overview

Load Custom Data

When you bind an editor to data from a Web API service, assign the data type to the component’s T parameter and use the CustomData property to implement custom data load logic.

View Example: Data Editors for Blazor - Custom data binding

You can also enable Virtual Scrolling to improve client-side performance.

Items

The <DxComboBox> drop-down window displays a list of predefined items. Set the AllowUserInput property to true to allow users to type values into the ComboBox’s edit box.

<DxComboBox Data="@Cities"
            AllowUserInput="true"
            NullText="Select City ..."
            @bind-Value="@Value"
            @bind-Text="@Text">
</DxComboBox>

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

  string Text { get; set; } = "New York";
  string Value { get; set; }
}

Use the Text property to specify an editor value in code. To respond to an editor’s text change, handle the TextChanged event.

The table below lists API members related to the ComboBox item collection:

Member	Description
Value	Specifies the ComboBox’s selected value/item.
ValueChanged	Fires when the ComboBox’s selected value changes.
ValueFieldName	Specifies the data source field that populates values for the ComboBox’s items.
ItemTemplate	Specifies a template used to display the ComboBox’s items.
DropDownVisible	Specifies the current state (displayed/hidden) of a drop-down window.
ShowDropDown()	Displays an editor’s drop-down window.

Clear Button and Placeholder

Set the ClearButtonDisplayMode property to Auto to show the Clear button when the editor has a non-null value. Users can click this button to clear the editor’s value (set it to null).

Use the NullText property to display the prompt text (placeholder) in the editor when its value is null.

Razor

<DxComboBox NullText="Select a country..."
            Data="@CountryData.Countries"
            @bind-Value="@CurrentCountry"
            TextFieldName="@nameof(Country.CountryName)"
            ClearButtonDisplayMode="DataEditorClearButtonDisplayMode.Auto">
</DxComboBox>

@code {
    Country CurrentCountry { get; set; } = CountryData.Countries[1];
}

Country

public class Country {
    public int Id { get; set; }
    public string CountryName { get; set; }
}

public static class CountryData {
    private static readonly Lazy<List<Country>> countries = new Lazy<List<Country>>(() => {
        return new List<Country>()
        {
            new Country() { Id = 0, CountryName = "USA" },
            new Country() { Id = 1, CountryName = "Germany" },
            new Country() { Id = 2, CountryName = "Japan" }
        };
    });
    public static List<Country> Countries { get { return countries.Value; } }
}

Run Demo: ComboBox - Clear Button and Placeholder

Note

If you use the EditBoxTemplate property and need to show the clear button and placeholder, you should also add a DxInputBox object to the template markup.

Cascading Comboboxes

The <DxComboBox> allows you to create cascade lists - populate one ComboBox with items based on the user selection from another ComboBox. Use the Value property to access the selected item. To respond to the selected item change, handle the ValueChanged event.

Razor

@using CountryCityData

<DxComboBox Data="@Countries"
            TextFieldName="@nameof(Country.CountryName)"
            Value="@CurrentCountry"
            ValueChanged="@((Country country) => SelectedCountryChanged(country))"
            AllowUserInput="true">
</DxComboBox>
<DxComboBox Data="@CurrentCountryCities"
            TextFieldName="@nameof(City.CityName)"
            @bind-Value="@CurrentCity"
            AllowUserInput="true">
</DxComboBox>

@code {
    List<Country> Countries { get; set; } = CountryData.Countries;
    List<City> CurrentCountryCities { get; set; } = new List<City>();
    Country CurrentCountry { get; set; } = CountryData.Countries[1];
    City CurrentCity { get; set; } = CityData.Cities[4];

    protected override void OnInitialized() {
        base.OnInitialized();
        SelectedCountryChanged(CurrentCountry);
    }

    void SelectedCountryChanged(Country country) {
        CurrentCountry = country;
        CurrentCountryCities = CityData.Cities.FindAll(city => city.CountryId == CurrentCountry.Id);
        CurrentCity = CurrentCountryCities[0];
    }
}

CountryCity

namespace CountryCityData {
    public class City {
        public int Id { get; set; }
        public int CountryId { get; set; }
        public string CityName { get; set; }
    }

    public static class CityData {
        private static readonly Lazy<List<City>> cities = new Lazy<List<City>>(() => {
            return new List<City>() {
            new City() { Id = 0, CountryId = 0, CityName = "Washington" },
            new City() { Id = 1, CountryId = 0, CityName = "New York" },
            new City() { Id = 2, CountryId = 0, CityName = "Los Angeles" },
            new City() { Id = 3, CountryId = 1, CityName = "Berlin" },
            new City() { Id = 4, CountryId = 1, CityName = "Munich" },
            new City() { Id = 5, CountryId = 1, CityName = "Hamburg" },
            new City() { Id = 6, CountryId = 2, CityName = "Tokyo" },
            new City() { Id = 7, CountryId = 2, CityName = "Osaka" },
            new City() { Id = 8, CountryId = 2, CityName = "Yokohama" }
        };
        });
        public static List<City> Cities { get { return cities.Value; } }
    }
    public class Country {
        public int Id { get; set; }
        public string CountryName { get; set; }
    }

    public static class CountryData {
        private static readonly Lazy<List<Country>> countries = new Lazy<List<Country>>(() => {
            return new List<Country>()
                {
            new Country() { Id = 0, CountryName = "USA" },
            new Country() { Id = 1, CountryName = "Germany" },
            new Country() { Id = 2, CountryName = "Japan" }
        };
        });
        public static List<Country> Countries { get { return countries.Value; } }
    }
}

Run Demo: ComboBox - Cascading Lists View Example: Grid - Implement Cascading ComboBoxes

Watch Video: ComboBox - Multiple Columns and Cascade Lists

Filter Data

<DxComboBox> allows you to dynamically filter list items based on the text typed into the editor. Use the FilteringMode property to enable filtering and specify the filter mode (Contains or StartsWith).

<DxComboBox FilteringMode="DataGridFilteringMode.Contains" Data="@Data" @bind-Value="@Value"></DxComboBox>

@code {
    IEnumerable<Country> Data;
    Country Value { get; set; }
}

The ComboBox automatically highlights the first match in the filtered list. Users can press the Enter key to select the value.

Run Demo: ComboBox - Incremental Filtering

Note

If you use the EditBoxTemplate property and need to enable filter mode, you should add a DxInputBox object to the template markup.

Multiple Columns

The ComboBox control can display data across multiple columns. Follow the steps below to create columns:

1. Add a <Columns> tag to the component’s markup to declare the column collection.

2. Populate the Columns collection with DxListEditorColumn objects. These objects include the following properties:

   • FieldName - Specifies the data source field that populates column items.
   • Caption - Specifies the column header.
   • Visible - Specifies column visibility.
   • VisibleIndex - Specifies column position.
   • Width - Specifies column width.

To format an edit box’s value, use the EditFormat property.

Razor

@using StaffData

<DxComboBox Data="@Staff.DataSource"
            @bind-Value="@SelectedPerson"
            EditFormat ="{1} {2}">
    <Columns>        
        <DxListEditorColumn FieldName="Id" Width="50px" />
        <DxListEditorColumn FieldName="FirstName" Caption="Name"/>
        <DxListEditorColumn FieldName="LastName" Caption="Surname"/>
    </Columns>
</DxComboBox>

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

StaffData

namespace StaffData {
    public static class Staff {
        private static readonly Lazy<List<Person>> dataSource = new Lazy<List<Person>>(() => {
            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 dataSource;
        });
        public static List<Person> DataSource { get { return dataSource.Value; } }
    }

    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 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);
        }
    }

    public enum Department { Motors, Electronics, Software }

}

Run Demo: ComboBox – Multiple Columns

Watch Video: ComboBox - Multiple Columns and Cascade Lists

Customization

The ComboBox component allows you to customize its appearance and the appearance of its items.

Appearance Customization

Use the SizeMode property to specify the size of a ComboBox. The code below applies different sizes to ComboBox components.

<DxComboBox Data="@Cities"
            NullText="Select City ..."
            @bind-Value="@Value"
            SizeMode="SizeMode.Small">
</DxComboBox>

<DxComboBox Data="@Cities"
            NullText="Select City ..."
            @bind-Value="@Value"
            SizeMode="SizeMode.Medium">
</DxComboBox>

<DxComboBox Data="@Cities"
            NullText="Select City ..."
            @bind-Value="@Value"
            SizeMode="SizeMode.Large">
</DxComboBox>

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

    string Value { get; set; }
}

To customize ComboBox input, use the InputCssClass property. The following code snippet applies a custom style to input borders:

<style>
    .my-style {
        border: 2px dotted orange;
    }
</style>

<DxComboBox Data="@Cities"
            NullText="Select City ..."
            @bind-Value="@Value"
            InputCssClass="my-style">
</DxComboBox>

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

    string Value { get; set; }
}

For more information, refer to the following help topics:

• Size Modes
• CSS Classes

Items Customization

The ItemTemplate property allows you to customize the appearance of the ComboBox’s items. Use the template’s context parameter to access a data object and its fields (for instance, you can get the value of a data field).

The example below demonstrates how to display the ComboBox’s items in a card-like view. Each item shows an employee’s first name, last name, photo, and phone number.

Razor

@inject NwindDataService NwindDataService
<DxComboBox Data="@Data"
            @bind-Value="@Value"
            CssClass="cw-480">
    <ItemTemplate>
        <div class="combobox-item-template">
            <img src="@StaticAssetUtils.GetImagePath(GetImageFileName(context))" />
            <div class="combobox-item-template-text">
                <span>@context.FirstName @context.LastName</span>
                <span class="combobox-item-template-employee-phone">@context.HomePhone</span>
            </div>
        </div>
    </ItemTemplate>
</DxComboBox>

@code {
    IEnumerable<Employee> Data { get; set; }
    Employee Value { get; set; }
    protected override async Task OnInitializedAsync() {
        Data = await NwindDataService.GetEmployeesAsync();
        Value = Data.FirstOrDefault();
    }
    string GetImageFileName(Employee employee) {
        return $"employees/item-template{employee.EmployeeId}.jpg";
    }
}

CSS

.combobox-item-template {
    display: flex;
    align-items: center;
}

.combobox-item-template > img {
    border-radius: 50%;
    width: 2rem;
    height: 2rem;
}

img + .combobox-item-template-text {
    margin-left: 1rem;
}

.combobox-item-template-text {
    display: flex;
    flex-flow: column;
}

.combobox-item-template-employee-phone {
    opacity: 0.65;
}

Employee.cs

public partial class Employee {
// ...
    public int EmployeeId { get; set; }
    public string LastName { get; set; }
    public string FirstName { get; set; }
    public string Title { get; set; }
    public string TitleOfCourtesy { get; set; }
    public Nullable<System.DateTime> BirthDate { get; set; }
    public Nullable<System.DateTime> HireDate { get; set; }
    public string Address { get; set; }
    public string City { get; set; }
    public string Region { get; set; }
    public string PostalCode { get; set; }
    public string Country { get; set; }
    public string HomePhone { get; set; }
    public string Extension { get; set; }
    public byte[] Photo { get; set; }
    public string Notes { get; set; }
    public Nullable<int> ReportsTo { get; set; }
    public string PhotoPath { get; set; }
    public string GroupName { get; set; }

    public virtual ICollection<Order> Orders { get; set; }

    public string Text => $"{FirstName} {LastName} ({Title})";
    public string FullName => $"{FirstName} {LastName}";
    public string ImageFileName => $"employees/{EmployeeId}.jpg";
}

Run Demo: ComboBox - ItemTemplate

Edit Box Customization

The EditBoxTemplate property allows you to customize the appearance of a ComboBox item displayed in the edit box. It can be the selected item or focused item when a user tries to select it.

The most popular usage scenario for the EditBoxTemplate property is to show item icons in the edit box.

Razor

<DxComboBox Data="@Items"
            @bind-Value="@Value"
            CssClass="cw-480" >
    <EditBoxTemplate>
        @GetTemplateContent(context)
    </EditBoxTemplate>
    ...
</DxComboBox>

@code {
    string Value { get; set; } = "Low";
    IEnumerable<string> Items = new List<string>() {"Low", "Normal", "High"};
    RenderFragment GetTemplateContent(string item) {
        return @<div class="template-container">
                   <svg class="@GetIconCssClass(item)" role="img">
                       <use href="@GetIconHref(item)"/>
                   </svg>
                   @item
               </div>;
    }
    string GetIconHref(string item) {
        return item != null ? StaticAssetUtils.GetImagePath($"icons/levels.svg#dx-{item.ToLower()}-level") : string.Empty;
    }
    string GetIconCssClass(string item) {
        var cssClass = "template-icon";
        if (item != null)
            cssClass += $" {item.ToLower()}-level";
        return cssClass;
    }
}

StaticAssetUtils

class StaticAssetUtils {
    static string libraryPath = System.Reflection.Assembly.GetExecutingAssembly().GetName().Name;

    public static string GetContentPath(string assetPath) {
        return $"./_content/{libraryPath}/{assetPath}";
    }

    public static string GetImagePath(string imageFileName) {
        return GetContentPath($"images/{imageFileName}");
    }
}

CSS

.template-container {
    display: flex;
    align-items: center;
}
.template-icon {
    fill: currentColor;
    width: 1rem;
    height: 1rem;
    margin-right: 0.375rem;
}
.low-level {
    color: #D73F3F;
}
.high-level {
    color: #1B8A10;
}
.normal-level {
    color: #406CF4;
}

You can also create an edit box template that supports user input and filter mode:

• Add <EditBoxTemplate>…</EditBoxTemplate> to the ComboBox markup.
• Declare a DxInputBox object within the EditBoxTemplate markup.
• Use the DxComboBox‘s InputCssClass to customize input box appearance.
• Optional. Set the DxComboBox.AllowUserInput to true.
• Optional. Use the DxComboBox.FilteringMode property to enable filter mode.
• Optional. Use the NullText property to display the prompt text in the edit box when the editor’s Value is null.

<DxComboBox Data="@Cities"
            @bind-Value="@CurrentCity"
            AllowUserInput="true"
            FilteringMode="DataGridFilteringMode.StartsWith"            
            NullText="Select City ..."
            ClearButtonDisplayMode="DataEditorClearButtonDisplayMode.Auto">
    <EditBoxTemplate>
        @if (context != null) {
            <span style="white-space: pre;">Selected City: </span>
        }
        <DxInputBox/>
    </EditBoxTemplate>
</DxComboBox>

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

Run Demo: ComboBox - EditBoxTemplate

Hide Built-In Drop-Down Button

Set the ShowDropDownButton property to false to hide the built-in button that invokes a drop-down menu. If you need a custom button, you can add a new command button.

Add Command Buttons

You can add custom command buttons to the ComboBox. Refer to Command Buttons for more information.

The code below adds the Add Employee button to the ComboBox.

Razor

<DxComboBox Data="@Data"
            TextFieldName="@nameof(Employee.Text)"
            @bind-Value="@SelectedEmployee"
            CssClass="dx-demo-editor-width">
    <Buttons>
        <DxEditorButton IconCssClass="editor-icon editor-icon-add"
                        Tooltip="Add an employee"
                        Click="@(_ => OnButtonClick())" />
    </Buttons>
</DxComboBox>

@code{
    IObserver<string> toasterRef;
    IEnumerable<Employee> Data { get; set; }
    Employee SelectedEmployee { get; set; }
    bool AddEmployeePopupVisible { get; set; }
    protected override async Task OnInitializedAsync() {
        Data = await NwindDataService.GetEmployeesAsync();
        SelectedEmployee = Data.FirstOrDefault();
    }
    void OnButtonClick() {
        AddEmployeePopupVisible = true;
    }
    void OnEmployeeAdded(Employee newEmployee) {
        AddEmployeePopupVisible = false;
        if (newEmployee != null) {
            Data = Data.Append(newEmployee);
        }
    }
}

AddEmployeePopup

<DxPopup
    @bind-Visible="@Visible"
    ShowFooter="true"
    HeaderText="Add Employee"
   >
    <BodyContentTemplate>
        <EmployeeEditForm @ref="@EditForm"/>
    </BodyContentTemplate>
    <FooterContentTemplate>
        <DxButton CssClass="popup-button my-1 ms-2" RenderStyle="ButtonRenderStyle.Primary" Text="Add" Click="@(() => ClosePopup(true))" />
        <DxButton CssClass="popup-button my-1 ms-2" RenderStyle="ButtonRenderStyle.Secondary" Text="Cancel" Click="@(() => ClosePopup(false))" />
    </FooterContentTemplate>
</DxPopup>

@code {
    [Parameter] public bool Visible { get; set; }
    [Parameter] public SizeMode? SizeMode { get; set; }
    [Parameter] public EventCallback<Employee> OnPopupClosed { get; set; }
    EmployeeEditForm EditForm { get; set; }
    async Task ClosePopup(bool isResultSuccessful) {
        var result = isResultSuccessful
            ? new Employee {
                FirstName = EditForm.FirstName,
                HireDate = EditForm.HiredDate,
                City = EditForm.City,
                Title = EditForm.Position
            }
            : null;
        await OnPopupClosed.InvokeAsync(result);
    }
}

EmployeeEditForm

<div class="d-flex flex-fill pt-1 pb-2 w-100">
    <DxFormLayout CssClass="w-100">
        <DxFormLayoutItem Caption="Employee First Name:"
                          CaptionPosition="CaptionPosition.Vertical"
                          CaptionCssClass="popup-demo-caption"
                          CssClass="popup-demo-item"
                          ColSpanMd="12">
            <div class="editor-demo-layout-item">
                <span class="editor-icon popup-icon-user"></span>
                <DxTextBox @bind-Text="@FirstName" CssClass="popup-demo-textbox" />
            </div>
        </DxFormLayoutItem>
        <DxFormLayoutItem Caption="Hired Date:"
                          CaptionPosition="CaptionPosition.Vertical"
                          CaptionCssClass="popup-demo-caption"
                          CssClass="popup-demo-item"
                          ColSpanMd="12">
            <div class="editor-demo-layout-item">
                <span class="editor-icon editor-icon-birthdate"></span>
                <DxDateEdit @bind-Date="@HiredDate" CssClass="popup-demo-textbox" />
            </div>
        </DxFormLayoutItem>
        <DxFormLayoutItem Caption="City:"
                          CaptionPosition="CaptionPosition.Vertical"
                          CaptionCssClass="popup-demo-caption"
                          CssClass="popup-demo-item"
                          ColSpanMd="12">
            <div class="editor-demo-layout-item">
                <span class="editor-icon editor-icon-city"></span>
                <DxTextBox @bind-Text="@City" CssClass="popup-demo-textbox" />
            </div>
        </DxFormLayoutItem>
        <DxFormLayoutItem Caption="Position:"
                          CaptionPosition="CaptionPosition.Vertical"
                          CaptionCssClass="popup-demo-caption"
                          CssClass="popup-demo-item"
                          ColSpanMd="12">
            <div class="editor-demo-layout-item">
                <span class="editor-icon popup-icon-position"></span>
                <DxComboBox CssClass="popup-demo-textbox"
                            Data="@(new List<string>{"Sales Representative", "Designer"})"
                            @bind-Value="@Position">
                </DxComboBox>
            </div>
        </DxFormLayoutItem>
    </DxFormLayout>
</div>

@code {
    public string FirstName { get; set; }
    public DateTime? HiredDate { get; set; }
    public string City { get; set; }
    public string Position { get; set; }
}

CSS

.dx-demo-form-layout-width {
    max-width: 640px;
    width: 100%;
}
.dx-demo-editor-width {
    max-width: 320px;
    width: 100%;
}

Run Demo: Editors - Command Buttons

Virtual Scrolling

When virtual scrolling is activated (ListRenderMode is set to Virtual), the ComboBox renders data on demand when a user scrolls its items.

<DxComboBox ListRenderMode="ListRenderMode.Virtual"
            Data="@Strings"
            @bind-Value="@Value" >
</DxComboBox>

Run Demo: ComboBox - Virtual Scrolling

Input Validation

You can add a standalone ComboBox or Form Layout component to Blazor’s standard EditForm. This form validates user input based on data annotation attributes defined in a model and indicates errors. To specify which ComboBox property takes part in input validation (Text or Value), use the ValidateBy property. If you handle the ValueChanged event and cannot use two-way binding, specify the ValueExpression property to identify the value passed to the event handler.

Razor

<EditForm Model="@starship" Context="EditFormContext">
    <DataAnnotationsValidator />
    <DxFormLayout >
        <DxFormLayoutItem Caption="Primary Classification:" ColSpanMd="6" >
            <Template >
                <DxComboBox
                            NullText="Select classification ..."
                            ClearButtonDisplayMode="DataEditorClearButtonDisplayMode.Auto"
                            @bind-Value="@starship.Classification"
                            Data="@(new List<string>() { "Defense", "Exploration", "Diplomacy" })"
                            ValidateBy="ComboBoxValidateBy.Value"
                />
            </Template >
        </DxFormLayoutItem >
        @*...*@
    </DxFormLayout>
</EditForm>

@code {
    private Starship starship=new Starship();
}

Starship

using System.ComponentModel.DataAnnotations;

public class Starship
{
    [Required]
    public string Classification { get; set; }
    // ...
}

For more information, refer to the following help topic: Validate Input.

Run Demo: Form Validation

Read-Only State

<DxComboBox> supports a read-only state. Set the ReadOnly property to true to activate this option.

<DxComboBox ReadOnly="true" 
            Data="@Strings" 
            @bind-Value="@Value" > 
</DxComboBox>

Run Demo: ComboBox - Read-Only and Disabled Modes

Drop-Down Window Width

Use the DropDownWidthMode property to specify the width of the drop-down list. The following values are available:

• ContentOrEditorWidth (Default) - The list displays item text completely. The minimum list width matches the editor.

  

• ContentWidth - The list width is equal to the width of the longest list item.

  

• EditorWidth - The list width matches the editor. List items are cut if they do not fit.

  

Note

When the ComboBox renders items on demand (ListRenderMode is set to Virtual), the list width can change while users scroll items.

The following code sets the width of the drop-down list to the editor width.

Razor

@using BlazorApp.Data

<DxComboBox Data="@Staff.DataSource"
            @bind-Value="@Value"
            TextFieldName="@nameof(Person.Text)"
            DropDownWidthMode="DropDownWidthMode.EditorWidth">
</DxComboBox>

@code {
  Person Value { 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;
using System.Collections.Generic;

namespace BlazorApp.Data {
    public static class Staff {
        private static readonly Lazy<List<Person>> dataSource = new Lazy<List<Person>>(() => {
            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 dataSource;
        });
        public static List<Person> DataSource { get { return dataSource.Value; } }
    }
}

Run Demo: ComboBox – Drop-Down List Width

Drop-Down Window Direction

Use the DropDownDirection property to specify the direction in which the ComboBox’s drop-down window is displayed relative to the input element. The default value is Down. The following code changes the direction to Up:

<DxComboBox Data="@Cities"
            @bind-Value="@Value"
            NullText="Select City ..."
            DropDownDirection="DropDownDirection.Up">
</DxComboBox>

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

    string Value { get; set; }
}

Note

If the editor is close to a browser window’s edge and there is not enough space to display the drop-down window in the specified direction, the drop-down window is displayed in the opposite direction.

HTML Attributes and Events

You can use HTML attributes and events to configure the ComboBox.

<DxComboBox Data="@Strings" 
            @bind-Value="@Value" 
            maxlength="10" 
            @onclick="MyFunction">
</DxComboBox>

@code {
    void MyFunction(){
        //...
    }
}

Troubleshooting

If a Blazor application throws unexpected exceptions, refer to the following help topic: Troubleshooting.

Implements

IHandleEvent

IHandleAfterRender

IAsyncDisposable

IComponent

Inheritance

Object

ComponentBase

DevExpress.Blazor.Base.DxAsyncDisposableComponent

DevExpress.Blazor.Base.DxDecoratedComponent

DxComponentBase

DxDataEditor<TData>

DxInputDataEditorBase<TData>

DevExpress.Blazor.Internal.DxComboBoxBase<TData, TValue>

DxComboBox<TData, TValue>