<style>
    .disabled-item {
        color: #D3D3D3;
        width:100%;
    }

    /* remove default padding so the user can't click the underlying element outside the template
        Note: this will also affect other dropdowns on the page
    */
    .ddl-item {
        padding: 4px 8px;
    }

    .k-popup ul.k-list li.k-item {
        padding: 0;
    }
</style>

@TheValue
<br />

<TelerikDropDownList Data="@myDdlData" TextField="MyTextField" ValueField="MyValueField" @bind-Value="@TheValue">
    <ItemTemplate>
        @{
            MyDdlModel item = context as MyDdlModel;
            <div @onclick:preventDefault="@item.IsDisabled" 
                 @onclick:stopPropagation="@item.IsDisabled"
                 class="@( item.IsDisabled ? "disabled-item ddl-item" : "ddl-item" )">
                    @item.MyTextField
            </div>
        }
    </ItemTemplate>
</TelerikDropDownList>


@code {
    int TheValue { get; set; } = 2;

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

    IEnumerable<MyDdlModel> myDdlData = Enumerable.Range(1, 20).Select(x => new MyDdlModel
    {
        MyTextField = "item " + x,
        MyValueField = x,
        IsDisabled = x % 3 == 0
    });
}

	<select @onchange="@OnChangedAsync">
		<option></option>
		@if (DataSource != null)
		{
			@foreach (var item in DataSource)
			{
				<option @key="item" value="@optionValueFunc(item)" selected="@(item.Equals(SelectedItem))">@optionTextFunc(item)</option>
			}
		}
	</select>

	#region Private Members

	private Func<TSource, object> optionTextFunc;
	private Func<TSource, object> optionValueFunc;
	private TSource selectedItem = default(TSource);

	#endregion

        #region Public Parameters

	/// <summary>
	/// A List of objects to bind against.
	/// </summary>
	[Parameter]
	public IList<TSource> DataSource { get; set; } = new List<TSource>();

	/// <summary>
        /// A lambda expression referencing the property containing the text to display to the end user. Example: @(c => c.DisplayName)
        /// </summary>
        [Parameter]
        public Expression<Func<TSource, object>> OptionText { get; set; }

	/// <summary>
        /// A lambda expression referencing the property containing the value for this object, usually an identifier. Example: @(c => c.Id)
        /// </summary>
        [Parameter]
        public Expression<Func<TSource, object>> OptionValue { get; set; }

	/// <summary>
        /// The item from the <see cref="DataSource" /> that has been selected.
        /// </summary>
        [Parameter]
        public TSource SelectedItem { get; set; }

	/// <summary>
	/// The callback event required for two-way binding.
	/// </summary>
	[Parameter]
        public EventCallback<TSource> SelectedItemChanged { get; set; }

        #endregion

	private async Task OnChangedAsync(ChangeEventArgs changeEventArgs)
        {
            await UpdateSelection(DataSource.FirstOrDefault(c => optionValueFunc(c).ToString() == changeEventArgs.Value.ToString()));
        }

	private async Task UpdateSelection(TSource item)
        {
            selectedItem = item;
            await SelectedItemChanged.InvokeAsync(selectedItem);
        }

	protected override async Task OnInitializedAsync()
	{
            if (optionTextFunc == null && OptionText != null)
            {
                optionTextFunc = OptionText.Compile();
            }
            if (optionValueFunc == null && OptionText != null)
            {
                optionValueFunc = OptionValue.Compile();
            }
            await Task.CompletedTask;          
        }

<TelerikDropDownList Data="@MyList" bind-Value=@MyItem>

</TelerikDropDownList>
 
@functions {
    protected List<string> MyList = new List<string>() { "a", "b", "c" };
 
    protected string MyItem { get; set; } = "b";
}