HandyControl/Net40/HandyControl_Net40/Interactivity/Behavior.cs

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()
        {
        }
    }
}