Add empty SplitButtonPage in ControlCatalog

samples/ControlCatalog/MainView.xaml

@@ -121,6 +121,9 @@
       <TabItem Header="Slider">
         <pages:SliderPage />
       </TabItem>
+      <TabItem Header="SplitButton">
+        <pages:SplitButtonPage />
+      </TabItem>
       <TabItem Header="SplitView">
         <pages:SplitViewPage />
       </TabItem>

samples/ControlCatalog/Pages/SplitButtonPage.xaml

@@ -0,0 +1,6 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="ControlCatalog.Pages.SplitButtonPage">
+  <StackPanel Orientation="Vertical" Spacing="4">
+  </StackPanel>
+</UserControl>

samples/ControlCatalog/Pages/SplitButtonPage.xaml.cs

@@ -0,0 +1,18 @@
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace ControlCatalog.Pages
+{
+    public class SplitButtonPage : UserControl
+    {
+        public SplitButtonPage()
+        {
+            InitializeComponent();
+        }
+
+        private void InitializeComponent()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+    }
+}