Added new kb article treeview-change-expand-collapse-icons (#2618)

* Added new kb article treeview-change-expand-collapse-icons

* Update knowledge-base/treeview-change-expand-collapse-icons.md

Co-authored-by: Dimo Dimov <[email protected]>

* Update knowledge-base/treeview-change-expand-collapse-icons.md

Co-authored-by: Dimo Dimov <[email protected]>

* Update knowledge-base/treeview-change-expand-collapse-icons.md

Co-authored-by: Dimo Dimov <[email protected]>

* Update knowledge-base/treeview-change-expand-collapse-icons.md

Co-authored-by: Dimo Dimov <[email protected]>

* chore(TreeView): address feedback

---------

Co-authored-by: KB Bot <[email protected]>
Co-authored-by: Nadezhda Tacheva <[email protected]>
Co-authored-by: Dimo Dimov <[email protected]>
Co-authored-by: Nadezhda Tacheva <[email protected]>

Author: 4 people

knowledge-base/treeview-change-expand-collapse-icons.md

@@ -0,0 +1,135 @@
+---
+title: Change the Expand and Collapse Icons in TreeView
+description: Learn how to customize the expand and collapse icons in the Telerik TreeView component for Blazor.
+type: how-to
+page_title: How to Customize Expand and Collapse Icons in Blazor TreeView
+slug: treeview-kb-change-expand-collapse-icons
+tags: blazor, treeview, icons, expand, collapse
+res_type: kb
+ticketid: 1656109
+---
+
+## Environment
+
+<table>
+    <tbody>
+        <tr>
+            <td>Product</td>
+            <td>TreeView for Blazor</td>
+        </tr>
+    </tbody>
+</table>
+
+## Description
+I want to customize the icons used for expanding and collapsing items in the [TreeView for Blazor]({%slug treeview-overview%}). 
+
+This knowledge base article answers the following questions:
+- How can I use custom icons for the TreeView expand and collapse functionality?
+- Is it possible to change the default expand and collapse icons in the TreeView for Blazor?
+
+## Solution
+
+You can change the expand/collapse icons in the TreeView by overriding the built-in icons with other icons using [custom CSS rules]({%slug themes-override%}). In addition, you can use the `Class` parameter of the TreeView to add a custom CSS Class and modify a specific instance of the TreeView, instead of all instances on the page.
+
+>caption Change the expand/collapse icons in TreeView
+
+````CSHTML
+@* In Telerik.UI.for.Blazor version 4.3.0 and later, the components use SVG icons by default. Use the following CSS for versions 4.3.0 and later. *@
+@* Render the desired SVG icon and inspect it with your dev tools to get its path. *@
+<style>
+    .custom-icons .k-treeview-toggle .k-svg-icon.k-svg-i-caret-alt-down svg path {
+        d: path("m382.059 158.059-126.06 126.06-126.061-126.06L96 192l159.999 160L416 192z");
+    }
+
+    .custom-icons .k-treeview-toggle .k-svg-icon.k-svg-i-caret-alt-right svg path {
+        d: path("m158.059 129.941 126.06 126.06-126.06 126.061L192 416l160-159.999L192 96z");
+</style>
+
+@* In Telerik.UI.for.Blazor version below 4.3.0, the components use Font icons by default. Use this CSS for versions prior to 4.3.0. *@
+@* Copy the unicode of your desired icon from the Progress Design System - https://www.telerik.com/design-system/docs/foundation/iconography/icon-list/ *@
+
+@* <style>
+    .custom-icons .k-treeview-toggle .k-icon.k-i-caret-alt-down::before {
+        content: "\e015";
+    }
+
+    .custom-icons .k-treeview-toggle .k-icon.k-i-caret-alt-right::before {
+        content: "\e014";
+    }
+</style> *@
+
+<TelerikTreeView Class="custom-icons"
+                 Data="@FlatData"
+                 @bind-ExpandedItems="@ExpandedItems" />
+
+@code {
+    private IEnumerable<TreeItem> FlatData { get; set; }
+
+    private IEnumerable<object> ExpandedItems { get; set; } = new List<TreeItem>();
+
+    protected override void OnInitialized()
+    {
+        FlatData = GetFlatData();
+
+        ExpandedItems = FlatData.Where(x => x.HasChildren == true && x.Id != 3).ToList();
+    }
+
+    List<TreeItem> GetFlatData()
+    {
+        List<TreeItem> items = new List<TreeItem>();
+
+        items.Add(new TreeItem()
+            {
+                Id = 1,
+                Text = "wwwroot",
+                ParentId = null,
+                HasChildren = true,
+                Icon = SvgIcon.Folder
+            });
+        items.Add(new TreeItem()
+            {
+                Id = 2,
+                Text = "css",
+                ParentId = 1,
+                HasChildren = true,
+                Icon = SvgIcon.Folder
+            });
+        items.Add(new TreeItem()
+            {
+                Id = 3,
+                Text = "js",
+                ParentId = 1,
+                HasChildren = true,
+                Icon = SvgIcon.Folder
+            });
+        items.Add(new TreeItem()
+            {
+                Id = 4,
+                Text = "site.css",
+                ParentId = 2,
+                Icon = SvgIcon.Css
+            });
+        items.Add(new TreeItem()
+            {
+                Id = 5,
+                Text = "scripts.js",
+                ParentId = 3,
+                Icon = SvgIcon.Js
+            });
+
+        return items;
+    }
+
+    public class TreeItem
+    {
+        public int Id { get; set; }
+        public string Text { get; set; }
+        public int? ParentId { get; set; }
+        public bool HasChildren { get; set; }
+        public ISvgIcon Icon { get; set; }
+    }
+}
+````
+## See Also
+- [TreeView Overview]({%slug treeview-overview%}) 
+- [Telerik Icons List](https://www.telerik.com/design-system/docs/foundation/iconography/icon-list/)