<TelerikButton Class="tooltip-target" Title="Telerik Tooltip">Button</TelerikButton>

<TelerikDropDownList Data="@ListItems"
                     @bind-Value="@SelectedValue"
                     TextField="@nameof(ListItem.Text)"
                     ValueField="@nameof(ListItem.Id)"
                     AdaptiveMode="@AdaptiveMode.Auto"
                     Width="300px" />
<TelerikTooltip TargetSelector=".tooltip-target"
                ShowOn="@TooltipShowEvent.Hover" />

@code {
    private List<ListItem> ListItems { get; set; } = new();

    private int SelectedValue { get; set; } = 3;

    protected override void OnInitialized()
    {
        ListItems = new List<ListItem>();
        for (int i = 1; i <= 5; i++)
        {
            ListItems.Add(new ListItem()
            {
                Id = i,
                Text = $"Item {i}",
                Category = $"Category {i % 6 + 1}"
            });
        }
        base.OnInitialized();
    }

    public class ListItem
    {
        public int Id { get; set; }
        public string Text { get; set; } = string.Empty;
        public string Category { get; set; } = string.Empty;
    }
}

Error: System.ArgumentNullException: Value cannot be null. (Parameter 'nullableType')

<TelerikFilter @bind-Value="@AdvancedFilterValue">
	<FilterFields>
		@foreach (var it in GridDef.ColStore.Where(x => x.Verejny == true))
		{
			<FilterField Name="@it.FldName" Type="@it.FldType" Label="@it.VerejnyNazev"></FilterField>
		}
	</FilterFields>
</TelerikFilter>

@inject IJSRuntime js

<TelerikButton OnClick="@( () => WindowVisible = true )">Show Window</TelerikButton>

<TelerikWindow @bind-Visible="@WindowVisible"
               Modal="true">
    <WindowActions>
        <WindowAction Name="Minimize" />
        <WindowAction Name="Close" />
    </WindowActions>
    <WindowTitle>
        Window Title
    </WindowTitle>
    <WindowContent>
        <p>Window Content</p>
        <TelerikButton OnClick="@OnShowDialogButtonClick">Show Dialog</TelerikButton>
    </WindowContent>
</TelerikWindow>

<TelerikDialog @bind-Visible="@DialogVisible"
               Width="300px"
               Class="dialog-on-window">
    <DialogTitle>
        Dialog Title
    </DialogTitle>
    <DialogContent>
        <p>Dialog Content</p>
    </DialogContent>
    <DialogButtons>
        <TelerikButton OnClick="@( () => OnDialogButtonClick(true) )">OK</TelerikButton>
    </DialogButtons>
</TelerikDialog>

<script suppress-error="BL9992">
    function bringDialogToTop() {
        var dialogWrapper = document.querySelector(".dialog-on-window").closest(".k-dialog-wrapper");
        if (dialogWrapper) {
            dialogWrapper.style.zIndex = parseInt(dialogWrapper.style.zIndex) + 2;
        }
    }
</script>

@code {
    private bool WindowVisible { get; set; }

    private bool DialogVisible { get; set; }

    private bool ShouldFocusDialog { get; set; }

    private void OnShowDialogButtonClick()
    {
        DialogVisible = true;
        ShouldFocusDialog = true;
    }

    private void OnDialogButtonClick(bool result)
    {
        DialogVisible = false;
    }

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (ShouldFocusDialog)
        {
            ShouldFocusDialog = false;
            await Task.Delay(1);

            await js.InvokeVoidAsync("bringDialogToTop");
        }

        await base.OnAfterRenderAsync(firstRender);
    }
}

DropDownTreeValue1: @DropDownTreeValue1
<br />
DropDownTreeValue2: @DropDownTreeValue2

<br />

Bug:
<TelerikDropDownTree Data="@DropDownTreeData"
                     @bind-Value="@DropDownTreeValue1"
                     @bind-ExpandedItems="@DropDownTreeExpandedItems"
                     Width="300px">
</TelerikDropDownTree>

Workaround:
<TelerikDropDownTree Data="@DropDownTreeData"
                     @bind-Value="@DropDownTreeValue2"
                     @bind-ExpandedItems="@DropDownTreeExpandedItems"
                     Width="300px">
</TelerikDropDownTree>

@* Render DropDownTree after setting Data *@
@if (DropDownTreeData is not null)
{
    <span>Workaround:</span>
    <TelerikDropDownTree Data="@DropDownTreeData"
                        @bind-Value="@DropDownTreeValue1"
                        @bind-ExpandedItems="@DropDownTreeExpandedItems"
                        Width="300px">
    </TelerikDropDownTree>
}

@code {
    private List<TreeItem>? DropDownTreeData { get; set; }

    private int DropDownTreeValue1 { get; set; }
    private int DropDownTreeValue2 { get; set; }

    private IEnumerable<object> DropDownTreeExpandedItems { get; set; } = new List<TreeItem>();

    protected override async Task OnInitializedAsync()
    {
        DropDownTreeValue1 = 3;
        await Task.Delay(1000);
        DropDownTreeData = LoadFlatData();

        // Set DropDownTree Value after setting Data
        DropDownTreeValue2 = 3;

        DropDownTreeExpandedItems = DropDownTreeData.Where(x => x.ParentId is null && x.HasChildren);
    }

    private int TreeLevels { get; set; } = 3;
    private int RootItems { get; set; } = 2;
    private int ItemsPerLevel { get; set; } = 2;
    private int IdCounter { get; set; }

    private List<TreeItem> LoadFlatData()
    {
        List<TreeItem> items = new List<TreeItem>();

        PopulateChildren(items, null, 1);

        return items;
    }

    private void PopulateChildren(List<TreeItem> items, int? parentId, int level)
    {
        var itemCount = level == 1 ? RootItems : ItemsPerLevel;
        for (int i = 1; i <= itemCount; i++)
        {
            var itemId = ++IdCounter;
            items.Add(new TreeItem()
            {
                Id = itemId,
                ParentId = parentId,
                HasChildren = level < TreeLevels,
                Text = $"Level {level} Item {i} Id {itemId}",
                Value = itemId
            });

            if (level < TreeLevels)
            {
                PopulateChildren(items, itemId, level + 1);
            }
        }
    }

    public class TreeItem
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
        public bool HasChildren { get; set; }
        public string Text { get; set; } = string.Empty;
        public int Value { get; set; }
    }
}