support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Interactivity/Behavior.cs

@@ -0,0 +1,87 @@
+using System;
+using System.Globalization;
+using System.Windows;
+using System.Windows.Media.Animation;
+
+namespace HandyControl.Interactivity
+{
+    public abstract class Behavior : Animatable, IAttachedObject
+    {
+        private DependencyObject _associatedObject;
+        private readonly Type _associatedType;
+
+        internal Behavior(Type associatedType)
+        {
+            _associatedType = associatedType;
+        }
+
+        protected DependencyObject AssociatedObject
+        {
+            get
+            {
+                ReadPreamble();
+                return _associatedObject;
+            }
+        }
+
+        protected Type AssociatedType
+        {
+            get
+            {
+                ReadPreamble();
+                return _associatedType;
+            }
+        }
+
+        public void Attach(DependencyObject dependencyObject)
+        {
+            if (!Equals(dependencyObject, AssociatedObject))
+            {
+                if (AssociatedObject != null)
+                    throw new InvalidOperationException(ExceptionStringTable
+                        .CannotHostBehaviorMultipleTimesExceptionMessage);
+                if (dependencyObject != null && !AssociatedType.IsInstanceOfType(dependencyObject))
+                    throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture,
+                        ExceptionStringTable.TypeConstraintViolatedExceptionMessage,
+                        new object[] {GetType().Name, dependencyObject.GetType().Name, AssociatedType.Name}));
+                WritePreamble();
+                _associatedObject = dependencyObject;
+                WritePostscript();
+                OnAssociatedObjectChanged();
+                OnAttached();
+            }
+        }
+
+        public void Detach()
+        {
+            OnDetaching();
+            WritePreamble();
+            _associatedObject = null;
+            WritePostscript();
+            OnAssociatedObjectChanged();
+        }
+
+        DependencyObject IAttachedObject.AssociatedObject =>
+            AssociatedObject;
+
+        internal event EventHandler AssociatedObjectChanged;
+
+        protected override Freezable CreateInstanceCore()
+        {
+            return (Freezable) Activator.CreateInstance(GetType());
+        }
+
+        private void OnAssociatedObjectChanged()
+        {
+            AssociatedObjectChanged?.Invoke(this, new EventArgs());
+        }
+
+        protected virtual void OnAttached()
+        {
+        }
+
+        protected virtual void OnDetaching()
+        {
+        }
+    }
+}