/V4/PrismLibrary/Phone/Prism.Interactivity/DependencyPropertyListener.cs

//===================================================================================

// Microsoft patterns & practices

// Composite Application Guidance for Windows Presentation Foundation and Silverlight

//===================================================================================

// Copyright (c) Microsoft Corporation.  All rights reserved.

// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY

// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT

// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND

// FITNESS FOR A PARTICULAR PURPOSE.

//===================================================================================

// The example companies, organizations, products, domain names,

// e-mail addresses, logos, people, places, and events depicted

// herein are fictitious.  No association with any real company,

// organization, product, domain name, email address, logo, person,

// places, or events is intended or should be inferred.

//===================================================================================

using System;

using System.Windows;

using System.Windows.Data;



namespace Microsoft.Practices.Prism.Interactivity

{

    /// <summary>

    /// Registers a new dependency property for tracking data and provides

    /// notification on data changes.

    /// </summary>

    public class DependencyPropertyListener

    {

        private readonly DependencyProperty property;

        private static int index;

        private FrameworkElement target;



        /// <summary>

        /// Instantiates a new <see cref="DependencyPropertyListener"/>.

        /// </summary>

        /// <remarks>

        /// This registers creates an attached property with the name starting DependencyPropertyListener.  This

        /// attached property set on a <see cref="FrameworkElement"/> when <see cref="Attach"/> is called.</remarks>

        public DependencyPropertyListener()

        {

            this.property = 

                DependencyProperty.RegisterAttached(

                    "DependencyPropertyListener" + index++, 

                    typeof(object), 

                    typeof(DependencyPropertyListener), 

                    new PropertyMetadata(null, this.HandleValueChanged));

        }



        /// <summary>

        /// This event is raised when the attached property value changes.

        /// </summary>

        public event EventHandler<BindingChangedEventArgs> Changed;



        /// <summary>

        /// Attaches a <see cref="DependencyProperty"/> to a framework element with

        /// the provided <see cref="Binding"/>.

        /// </summary>

        /// <param name="element">The <see cref="FrameworkElement"/> to attach the monitoring dependency property to.</param>

        /// <param name="binding">The binding to use with the attached property.</param>

        public void Attach(FrameworkElement element, Binding binding)

        {

            if (element == null)

            {

                throw new ArgumentNullException("element");

            }

            

            if (this.target != null)

            {

                throw new InvalidOperationException("Cannot attach an already attached listener");

            }



            this.target = element;



            this.target.SetBinding(this.property, binding);

        }



        ///<summary>

        /// Detaches binding listener from target.

        ///</summary>

        public void Detach()

        {

            this.target.ClearValue(this.property);

            this.target = null;

        }



        private void HandleValueChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)

        {

            if (this.Changed != null)

            {

                this.Changed(this, new BindingChangedEventArgs(e));

            }

        }

    }

}