kb(DropDownButton): Add KB for item hierarchy

components/dropdownbutton/overview.md

@@ -176,3 +176,4 @@ The DropDownButton exposes a `FocusAsync` method that allows you to focus it pro
 * [DropDownButton API](slug:Telerik.Blazor.Components.TelerikDropDownButton)
 * [Live Demo: DropDownButton](https://demos.telerik.com/blazor-ui/dropdownbutton/overview)
 * [Live Demo: DropDownButton Items](https://demos.telerik.com/blazor-ui/dropdownbutton/items)
+* [Hierarchical DropDownButton Items](slug:dropdownbutton-kb-nested-item-hierarchy)

knowledge-base/dropdownbutton-nested-item-hierarchy.md

@@ -0,0 +1,180 @@
+---
+title: Nest DropDownButton Items in Hierarchy
+description: Learn how to nest dropdown buttons and use multiple sets of hierarchical dropdown items.
+type: how-to
+page_title: How to Nest DropDownButton Items in Hierarchy
+slug: dropdownbutton-kb-nested-item-hierarchy
+tags: blazor, dropdownbutton, hierarchy
+ticketid: 1628170, 1682574
+res_type: kb
+---
+
+## Environment
+
+<table>
+    <tbody>
+        <tr>
+            <td>Product</td>
+            <td>DropDownButton for Blazor</td>
+        </tr>
+    </tbody>
+</table>
+
+## Description
+
+This KB answers the following questions:
+
+* How to nest dropdown buttons and use multiple sets of dropdown items in a hierarchy?
+* How to allow nested layers of hierarchical items in the Telerik DropDownButton for Blazor? The UI should look like a multi-level Menu or ContextMenu.
+
+## Solution
+
+Here are two ways to achieve a hierarchy UI with a DropDownButton user interface.
+
+* [Indent the DropDownButton items with some empty space](#indent-dropdown-items).
+* [Use a Menu component and style it to look like a DropDownButton](#use-menu-component).
+
+Both examples below use [Telerik CSS theme variables](https://www.telerik.com/design-system/docs/themes/kendo-themes/default/theme-variables/) to avoid the need to hard-code custom style values.
+
+### Indent Dropdown Items
+
+1. Show parent-child relationships between the DropDownButton items by using empty space before each item text.
+1. (optional) [Add separators between groups of DropDownButton items](slug:dropdownbutton-kb-add-separator-between-items).
+
+>caption Apply padding to DropDownButton items to convey hierarchy
+
+````RAZOR
+<TelerikDropDownButton>
+    <DropDownButtonContent>DropDownButton</DropDownButtonContent>
+    <DropDownButtonItems>
+        <DropDownButtonItem>Level 1 Child 1</DropDownButtonItem>
+        <DropDownButtonItem>Level 1 Child 2</DropDownButtonItem>
+        <DropDownButtonItem><span class="pad"></span>Level 2 Child 1</DropDownButtonItem>
+        <DropDownButtonItem><span class="pad"></span>Level 2 Child 3</DropDownButtonItem>
+        <DropDownButtonItem><span class="pad"></span><span class="pad"></span>Level 3 Child 1</DropDownButtonItem>
+        <DropDownButtonItem>Level 1 Child 3</DropDownButtonItem>
+    </DropDownButtonItems>
+</TelerikDropDownButton>
+
+<style>
+    .pad {
+        padding-left: var(--kendo-spacing-6);
+    }
+</style>
+````
+
+### Use Menu Component
+
+1. Render a Menu component with a single root item.
+1. Define the item hierarchy with flat data or hierarchical data.
+1. Implement a [Menu `OnClick` event handler](slug:components/menu/events#onclick).
+
+>caption Style a Menu to look like a DropDownButton
+
+````RAZOR
+<TelerikMenu Data="@MenuItems"
+             Class="menu-button"
+             TItem="@MenuItem"
+             OnClick="@OnMenuItemClick">
+</TelerikMenu>
+
+<style>
+    .menu-button {
+        display: inline-block;
+        color: var(--kendo-color-on-base);
+    }
+
+        .menu-button > .k-item {
+            background: var(--kendo-color-base);
+            color: var(--kendo-color-on-base);
+            border: 1px solid var(--kendo-color-border);
+            border-radius: var(--kendo-border-radius-md);
+        }
+
+            .menu-button > .k-item:hover {
+                background: var(--kendo-color-base-hover);
+            }
+
+            .menu-button > .k-item.k-menu-item:active {
+                color: var(--kendo-color-on-base);
+                background: var(--kendo-color-base-active);
+            }
+
+            .menu-button > .k-item.k-menu-item:focus {
+                box-shadow: 0 0 0 2px rgba(0,0,0,.08);
+            }
+
+            /* optional: hide the expand arrow */
+            .menu-button > .k-item .k-menu-expand-arrow {
+                /*display: none;*/
+            }
+
+            .menu-button > .k-item > .k-menu-link {
+                padding: var(--kendo-spacing-1) var(--kendo-spacing-2);
+            }
+</style>
+
+@code {
+    private void OnMenuItemClick(MenuItem clickedItem)
+    {
+        Console.WriteLine($"The user clicked on {clickedItem.Text}");
+    }
+
+    private List<MenuItem> MenuItems { get; set; } = new List<MenuItem>()
+    {
+        new MenuItem()
+        {
+            Id = 1,
+            Text = "Menu as DropDownButton"
+        },
+        new MenuItem()
+        {
+            Id = 2,
+            ParentId = 1,
+            Text = "Level 1 Child 1"
+        },
+        new MenuItem()
+        {
+            Id = 3,
+            ParentId = 1,
+            Text = "Level 1 Child 2"
+        },
+        new MenuItem()
+        {
+            Id = 4,
+            ParentId = 3,
+            Text = "Level 2 Child 1"
+        },
+        new MenuItem()
+        {
+            Id = 5,
+            ParentId = 3,
+            Text = "Level 2 Child 2"
+        },
+        new MenuItem()
+        {
+            Id = 6,
+            ParentId = 5,
+            Text = "Level 3 Child 1"
+        },
+        new MenuItem()
+        {
+            Id = 7,
+            ParentId = 1,
+            Text = "Level 1 Child 3"
+        }
+    };
+
+    public class MenuItem
+    {
+        public int Id { get; set; }
+        public int? ParentId { get; set; }
+        public string Text { get; set; } = string.Empty;
+    }
+}
+````
+
+## See Also
+
+* [DropDownButton Overview](slug:dropdownbutton-overview)
+* [Menu Overview](slug:menu-overview)