add style and demo

src/Shared/HandyControlDemo_Shared/ViewModel/Controls/SplitButtonDemoViewModel.cs

@@ -0,0 +1,17 @@
+using System;
+using GalaSoft.MvvmLight;
+using HandyControl.Controls;
+#if netle40
+using GalaSoft.MvvmLight.Command;
+#else
+using GalaSoft.MvvmLight.CommandWpf;
+# endif
+
+namespace HandyControlDemo.ViewModel
+{
+    public class SplitButtonDemoViewModel : ViewModelBase
+    {
+        public RelayCommand<string> SelectCmd => new Lazy<RelayCommand<string>>(() =>
+            new RelayCommand<string>(str => Growl.Info(str))).Value;
+    }
+}