Components / DropDownList

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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To use a Telerik DropDownList for Blazor

  1. add the TelerikDropDownList tag
  2. populate its Data property with the collection of items you want in the dropdown
  3. set the TextField and ValueField properties to point to the corresponding names of the model
  4. (optional) set the Value property to the initial value of the model.

Basic dropdownlist data binding and two-way value binding

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; }

    //Define a preselected value when the component initializes
    protected override void OnInitialized()
    {
        selectedValue = 3;
    }

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

The result from the code snippet above

Component namespace and reference

See the Component Reference section in the Data Binding article for details and examples.

Features

The DropDownList provides the following features:

  • Class - the CSS class that will be rendered on the main wrapping element of the dropdownlist.

  • Data - allows you to provide the data source. Required.

  • DefaultText - 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 - whether the component is enabled.

  • Id - renders as the id attribute on the <select /> element, so you can attach a <label for=""> to it.

  • TItem - 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 - 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.

  • TabIndex - the tabindex attribute rendered on the dropdown.

  • TextField - the name of the field from the model that will be shown to the user. Defaults to Text.

  • ValueField - the name of the field from the model that will be the underlying value. Defaults to Value.

  • Value and bind-Value- 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.

    The Value and ValueField can be of types:

    • number (such as int, double and so on)
    • string
    • Guid
    • Enum

  • Width - the width of the dropdown and the main element. 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.

  • Templates - they allow you to control the rendering of items in the component. See the Templates article for more details.

  • Validation - see the Input Validation article for more details.

The attributes below are set via nested tags:

<TelerikDropDownList>
    <DropDownListSettings>
        <DropDownListPopupSettings Height="..." />
    </DropDownListSettings>
</TelerikDropDownList>
  • Class - additional CSS class to customize the appearance of the DropDownList dropdown.
  • Height - the height of the expanded dropdown list element.
  • Width - the width of the expanded dropdown list element. If you don't specify a value, the dropdown width will match the main element which can help with responsive layouts and 100% widths.

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 dropodwn 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

See Also

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