support for .NET framework 3.5

Still have bugs

Net35/HandyControlDemo_Net35/Tools/AssemblyHelper.cs

@@ -0,0 +1,22 @@
+using System;
+
+namespace HandyControlDemo.Tools
+{
+    public class AssemblyHelper
+    {
+        private static readonly string NameSpaceStr = typeof(AssemblyHelper).Assembly.GetName().Name;
+
+        public static object CreateInternalInstance(string className)
+        {
+            try
+            {
+                var type = Type.GetType($"{NameSpaceStr}.{className}");
+                return type == null ? null : Activator.CreateInstance(type);
+            }
+            catch
+            {
+                return null;
+            }
+        }
+    }
+}