style building

src/Shared/HandyControl_Shared/Controls/SideMenu/SideMenu.cs

@@ -1,4 +1,5 @@
 using System.Windows;
+using HandyControl.Data;
 
 namespace HandyControl.Controls
 {
@@ -6,6 +7,41 @@ namespace HandyControl.Controls
     {
         private SideMenuItem _selectedItem;
 
+        private SideMenuItem _selectedHeader;
+
+        public SideMenu()
+        {
+            AddHandler(SideMenuItem.SelectedEvent, new RoutedEventHandler(SideMenuItemSelected));
+        }
+
+        private void SideMenuItemSelected(object sender, RoutedEventArgs e)
+        {
+            if (e.OriginalSource is SideMenuItem item)
+            {
+                if (item.Role == SideMenuItemRole.Item)
+                {
+                    if (_selectedItem != null)
+                    {
+                        _selectedItem.IsSelected = false;
+                    }
+
+                    _selectedItem = item;
+                    _selectedItem.IsSelected = true;
+                }
+                else
+                {
+                    if (_selectedHeader != null)
+                    {
+                        _selectedHeader.IsSelected = false;
+                    }
+
+                    _selectedHeader = item;
+                    _selectedHeader.IsSelected = true;
+                    _selectedHeader.SelectDefaultItem(_selectedItem);
+                }
+            }
+        }
+
         protected override DependencyObject GetContainerForItemOverride() => new SideMenuItem();
 
         protected override bool IsItemItsOwnContainerOverride(object item) => item is SideMenuItem;