Added new kb article treeview-disable-checkboxes (#2838)

* Added new kb article treeview-disable-checkboxes

* chore: polish example

---------

Co-authored-by: KB Bot <kb-bot@telerik.com>
Co-authored-by: Tsvetomir Hristov <106250052+Tsvetomir-Hr@users.noreply.github.com>

Author: 3 people

knowledge-base/treeview-disable-checkboxes.md

@@ -0,0 +1,154 @@
+---
+title: How to Disable Checkboxes for Certain TreeView Items
+description: Learn how to disable checkboxes for certain items in the TreeView component based on a condition
+type: how-to
+page_title: How to Disable Checkboxes for Certain TreeView Items
+slug: treeview-kb-disable-checkboxes
+tags: blazor, treeview, checkbox, disabled
+res_type: kb
+ticketid: 1681641
+---
+
+## Environment
+
+<table>
+    <tbody>
+        <tr>
+            <td>Product</td>
+            <td>TreeView for Blazor</td>
+        </tr>
+    </tbody>
+</table>
+
+## Description
+
+This knowledge base article answers the following questions:
+
+- How can I apply custom CSS to TreeView items conditionally?
+- How to use the [`OnItemRender` event](slug:treeview-events#onitemrender) in the TreeView for Blazor?
+- Is it possible to disable checkboxes for certain TreeView items?
+
+## Solution
+
+To disable checkboxes for specific TreeView items based on a condition, use the `OnItemRender` event to apply a custom class to those items. Then, use CSS to style these items and their checkboxes as disabled. The following steps outline how to achieve this:
+
+1. Use the [`OnItemRender` event](slug:treeview-events#onitemrender) of the TreeView component to conditionally apply a custom CSS class.
+
+2. Define CSS styles that mimic the disabled state for the checkboxes and the items.
+
+3. Ensure your TreeView model includes a property (e.g., `IsActive`, `IsDisabled`)that you'll use to determine if an item's checkbox should be disabled.
+
+### Implementation
+
+````RAZOR
+<TelerikTreeView Data="@FlatData"
+                 @bind-ExpandedItems="@ExpandedItems"
+                 CheckBoxMode="@TreeViewCheckBoxMode.Multiple"
+                 @bind-CheckedItems="@CheckedItems"
+                 OnItemRender="@HandleOnItemRender">
+    <TreeViewBindings>
+        <TreeViewBinding IdField="Id" ParentIdField="ParentIdValue" TextField="Text" HasChildrenField="HasChildren" IconField="Icon" />
+    </TreeViewBindings>
+</TelerikTreeView>
+
+<style>
+    .@(DisabledCheckboxClass) .k-checkbox {
+        opacity: 0.5;
+        pointer-events: none;
+    }
+
+    .@(DisabledCheckboxClass) .k-treeview-leaf {
+        opacity: 0.7;
+        pointer-events: none;
+    }
+</style>
+
+@code {
+    private IEnumerable<TreeViewItem> FlatData { get; set; }
+    private IEnumerable<object> CheckedItems { get; set; } = new List<object>();
+    private IEnumerable<object> ExpandedItems { get; set; } = new List<TreeViewItem>();
+    private string DisabledCheckboxClass { get; set; } = "disabled-checkbox";
+
+    private void HandleOnItemRender(TreeViewItemRenderEventArgs args)
+    {
+        var item = args.Item as TreeViewItem;
+        if (!item.IsActive)
+        {
+            args.Class = DisabledCheckboxClass;
+        }
+    }
+    protected override void OnInitialized()
+    {
+        LoadFlatData();
+        ExpandedItems = FlatData.Where(x => x.HasChildren).ToList();
+    }
+
+    private void LoadFlatData()
+    {
+        List<TreeViewItem> items = new List<TreeViewItem>();
+
+        items.Add(new TreeViewItem()
+            {
+                Id = 1,
+                Text = "Root",
+                ParentIdValue = null,
+                HasChildren = true,
+                Icon = SvgIcon.Folder,
+                IsChecked = false,
+                IsActive = true
+            });
+
+        Random rnd = new Random();
+        for (int i = 2; i <= 5; i++)
+        {
+            bool hasChildren = rnd.Next(0, 2) == 1;
+            items.Add(new TreeViewItem()
+                {
+                    Id = i,
+                    Text = $"Folder {i}",
+                    ParentIdValue = 1,
+                    HasChildren = hasChildren,
+                    Icon = hasChildren ? SvgIcon.Folder : SvgIcon.File,
+                    IsChecked = false,
+                    IsActive = rnd.Next(0, 2) == 1
+                });
+
+            if (hasChildren)
+            {
+                for (int j = 1; j <= rnd.Next(1, 4); j++)
+                {
+                    int childId = i * 10 + j;
+                    items.Add(new TreeViewItem()
+                        {
+                            Id = childId,
+                            Text = $"File {childId}",
+                            ParentIdValue = i,
+                            HasChildren = false,
+                            Icon = SvgIcon.File,
+                            IsChecked = false,
+                            IsActive = rnd.Next(0, 2) == 1
+                        });
+                }
+            }
+        }
+
+        FlatData = items;
+    }
+
+    public class TreeViewItem
+    {
+        public int Id { get; set; }
+        public string Text { get; set; } = string.Empty;
+        public int? ParentIdValue { get; set; }
+        public bool HasChildren { get; set; }
+        public ISvgIcon? Icon { get; set; }
+        public bool IsChecked { get; set; }
+        public bool IsActive { get; set; }
+    }
+}
+````
+
+## See Also
+
+- [TreeView Overview](slug:treeview-overview)
+- [TreeView OnItemRender Event](slug:treeview-events#onitemrender)