Components / DropDownList

Blazor DropDownList Overview

The Blazor DropDownList component allows the user to choose an option from a predefined set of choices presented in a dropdown popup. The developer can control the data, sizes, and various appearance options like class and templates.

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Creating DropDownList

  1. Use the TelerikDropDownList tag to add the component to your razor page.
  2. Populate its Data property with the collection of items you want to appear in the dropdown.
  3. set the TextField and ValueField properties to point to the corresponding names of the model
  4. Bind the value of the component to a variable of the same type as the type defined in the ValueField parameter.
  5. (optional) enable features like filtering and clear button
  6. (optional) set the Value property to the initial value of the model.

DropDownList data binding, two-way value binding and main features

Selected value: @selectedValue
<br />

<TelerikDropDownList Data="@myDdlData" TextField="MyTextField" ValueField="MyValueField" @bind-Value="selectedValue">
</TelerikDropDownList>

@code {
    //in a real case, the model is usually in a separate file
    //the model type and value field type must be provided to the dropdpownlist
    public class MyDdlModel
    {
        public int MyValueField { get; set; }
        public string MyTextField { get; set; }
    }

    int selectedValue { get; set; }

    IEnumerable<MyDdlModel> myDdlData = Enumerable.Range(1, 20).Select(x => new MyDdlModel { MyTextField = "item " + x, MyValueField = x });
}

Data Binding

The Blazor DropDownList requires a data source so that it can populate the dropdown with data. To provide a data source, use the Data property. Read more about the Blazor DropDownList data binding....

Filtering

The Blazor DropDownList has a built-in filter that narrows down the shown suggestions as the end-user types. To configure this feature, use the Filterable parameter. Additionally, you can choose between different filter operators and configure after how many symbols the list with suggestions will appear. Read more about the Blazor DropDownList filter....

Grouping

The Blazor DropDownList enables you to group the listed suggestions into categories so you can help the end-user to browse faster through longer lists. Read more about the Blazor DropDownList grouping....

Templates

You can use the functionality of the built-in templates and customize the default rendering of the component. Read more about the Blazor DropDownList templates....

Validation

You can ensure that the component value is acceptable by using the built-in validation. Read more about input validation....

Virtualization

By virtualizing the elements in the dropdown, you can use huge data sources without performance issues. The UI virtualization works with both local and remote data. Read more about the Blazor DropDownList virtualization...

Adaptive Rendering

The component supports different popup rendering depending on the screen size. Read more about the Adaptive Rendering functionality and how to enable it...

Parameters

The DropDownList provides various parameters that allow you to configure the component:

Parameter Type Description
AdaptiveMode AdaptiveMode
(None)		 The adaptive mode of the component.
Data IEnumerable<TItem> allows you to provide the data source. Required.
DefaultText string simple hint to be displayed when no item is selected yet. In order for it to be shown, the Value parameter should be set to a default value depending on the type defined in the ValueField parameter. For example, 0 for an int, and null for an int? or string. You need to make sure that it does not match the value of an existing item in the data source. See the first example in the Examples section in this article and in the Input Validation article.
Enabled bool whether the component is enabled.
Filterable bool whether filtering is enabled for the end user.
FilterDebounceDelay int
150		 Time in milliseconds between the last typed symbol and the filter input value update. Applicable to filtering only. Use it to balance between client-side performance and number of database queries.
FilterOperator StringFilterOperator
(StartsWith)		 the method of filtering the items.
Id string renders as the id attribute on the <select /> element, so you can attach a <label for=""> to it.
TItem Type the type of the model to which the component is bound. Required if you can't provide Data or Value. Determines the type of the reference object.
TValue Type the type of the value field from the model to which the component is bound. Required if you can't provide Data or Value. Determines the type of the reference object. The type of the values can be:
- number (such as int, double, and so on)
- string
- Guid
- Enum
Title string The title text rendered in the header of the popup(action sheet). Applicable only when AdaptiveMode is set to Auto.
TabIndex int? the tabindex attribute rendered on the dropdown.
TextField string
(Text)		 the name of the field from the model that will be shown to the user.
ValueField string
(Value)		 the name of the field from the model that will be the underlying value.
Value and bind-Value TValue get/set the value of the component, can be used for binding. If you set it to a value allowed by the model class value field, the corresponding item from the data collection will be pre-selected. Use the bind-Value syntax for two-way binding, for example, to a variable of your own.

Styling and Appearance

The following parameters enable you to customize the appearance of the Blazor DropDownList:

Parameter Type Description
Class string The CSS class that will be rendered on the main wrapping element of the component. Use it to override the theme or apply custom styles.
Width string The width of the component. It will target both the dropdown and the main element if the dropdown has no specific width set. The default Width value is null, but the theme applies 100%. Use the Width property or custom CSS to set another value in any supported unit.

You can find more options for customizing the DropDownList styling in the Appearance article.

The popup of the component can be additionally customized via nested tags:

<TelerikDropDownList>
    <DropDownListSettings>
        <DropDownListPopupSettings Height="..." />
    </DropDownListSettings>
</TelerikDropDownList>

The DropDownList provides the following popup settings:

Parameter Type Description
AnimationDuration int The animation duration of the popup in milliseconds.
Class string Additional CSS class to customize the appearance of the popup.
Height string The height of the popup.
MinHeight string The minimum height of the popup.
MinWidth string The minimum width of the popup.
MaxHeight string The maximum height of the popup.
MaxWidth string The maximum width of the popup.
Width string The width of the popup. If you don't specify a value, the dropdown width will match the anchor element width which can help with responsive layouts and 100% widths.

The DropDownList is a generic component and its type comes from the model it is bound to and from the value field type. See the Component Reference section in the Data Binding article for details and examples.

Add a reference to the component instance to use the DropDownList's methods.

Method Description
Close Closes the popup.
FocusAsync Focuses the main element of the component. Always await this call, as it relies on JSInterop.
Open Opens the popup. 
<TelerikDropDownList @ref="@DropDownListRef"
                     Data="@DropDownListData"
                     @bind-Value="@DropDownListValue" 
                     Width="300px"/>

<TelerikButton OnClick="@OpenPopup">Open Popup</TelerikButton>

@code {
    private TelerikDropDownList<string, string> DropDownListRef { get; set; }

    private string DropDownListValue { get; set; }

    private List<string> DropDownListData { get; set; } = new List<string> { "first", "second", "third" };

    private void OpenPopup()
    {
        DropDownListRef.Open();
    }
}

Selected Item and DefaultText

By default, if no Value is provided and no DefaultText is defined, the DropDownList will appear empty.

  • To display DefaultText - Value should be 0 or null depending on the data type you are using in the ValueField and the DefaultText should be defined.

  • To display a selected item when the component renders - provide the Value of the desired element. Note that it must match an item of the component's data source.

Examples

Default text (hint) to show when no actual item is selected

@MyStringItem
<TelerikDropDownList Data="@MyStringList" @bind-Value="@MyStringItem" DefaultText="Select something">
</TelerikDropDownList>

<br />
<br />

@MyIntItem
<TelerikDropDownList Data="@MyIntList" @bind-Value="@MyIntItem" DefaultText="Select another thing">
</TelerikDropDownList>

@code {
    protected List<string> MyStringList = new List<string>() { "first", "second", "third" };

    //Current value is null (no item is sellected) which allows the DefaultText to be displayed.
    protected string MyStringItem { get; set; }

    protected List<int> MyIntList = new List<int>() { 1, 2, 3 };

    //Current value is 0 (no item is sellected) which allows the DefaultText to be displayed.
    protected int MyIntItem { get; set; }
}

Get selected item from external code

@result
<br />

<TelerikDropDownList Data="@myDdlData" TextField="MyTextField" ValueField="MyValueField"
                     @bind-Value="@DdlValue" DefaultText="Select something">
</TelerikDropDownList>

<TelerikButton OnClick="@GetSelectedItem">Get Selected Item</TelerikButton>

@code {
    string result;
    int DdlValue { get; set; } = 5;
    void GetSelectedItem()
    {
        // extract the data item from the data source by using the value
        MyDdlModel selectedItem = myDdlData.Where(d => d.MyValueField == DdlValue).FirstOrDefault();
        if (selectedItem != null)
        {
            result = selectedItem.MyTextField;
        }
        else
        {
            result = "no item selected";
        }

        StateHasChanged();
    }

    public class MyDdlModel
    {
        public int MyValueField { get; set; }
        public string MyTextField { get; set; }
    }

    IEnumerable<MyDdlModel> myDdlData = Enumerable.Range(1, 20).Select(x => new MyDdlModel { MyTextField = "item " + x, MyValueField = x });
}

If you are looking for more fields from the view-model that describes the dropdown items, not just the Value, see the Get model from dropdown KB article and the OnChange event.

You may also want to review/join the discussion and Vote for this request: Binding DropDownList Value to complex model

Next Steps

See Also

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