/V4/PrismLibrary/Phone/Prism.Interactivity/BindingListener.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.Collections.Generic;

using System.Windows;

using System.Windows.Data;



namespace Microsoft.Practices.Prism.Interactivity

{

    /// <summary>

    /// The delegate to invoke when the value monitored by the <see cref="BindingListener"/> changes.

    /// </summary>

    /// <param name="sender">The sender of the event.</param>

    /// <param name="e">The binding changed information.</param>

    [System.Diagnostics.CodeAnalysis.SuppressMessage ("Microsoft.Design", "CA1003:UseGenericEventHandlerInstances")]

    public delegate void ChangedHandler(object sender, BindingChangedEventArgs e);



    /// <summary>

    /// Attaches a binding lister to a <see cref="FrameworkElement"/> to enable the use

    /// of binding expressions from items that don't support <see cref="Binding"/> expressions (e.g. Expression Blend

    /// Silverlight 3 Behaviors).

    /// </summary>

    /// <remarks>

    /// This was taken, with permission, from Peter Blois (http://blois.us/blog/2009/04/datatrigger-bindings-on-non.html)

    /// </remarks>

    public class BindingListener

    {

        private static readonly List<DependencyPropertyListener> freeListeners = new List<DependencyPropertyListener>();



        private readonly ChangedHandler changedHandler;

        private Binding binding;

        private DependencyPropertyListener listener;

        private FrameworkElement target;

        private object value;



        ///<summary>

        /// Intantiates a new instance of the BindingListener.

        ///</summary>

        ///<param name="changedHandler"></param>

        public BindingListener(ChangedHandler changedHandler)

        {

            this.changedHandler = changedHandler;

        }



        /// <summary>

        /// Gets or sets the <see cref="Binding"/> to when attaching the dependency property.

        /// </summary>

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Maintainability", "CA1500:VariableNamesShouldNotMatchFieldNames", MessageId = "value")]

        public Binding Binding

        {

            get { return this.binding; }

            set

            {

                this.binding = value;

                this.Attach();

            }

        }



        /// <summary>

        /// Gets or sets the framework element to attach the listener to.

        /// </summary>

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Maintainability", "CA1500:VariableNamesShouldNotMatchFieldNames", MessageId = "value")]

        public FrameworkElement Element

        {

            get { return this.target; }

            set

            {

                this.target = value;

                this.Attach();

            }

        }



        /// <summary>

        /// The value of the underlying monitored object.

        /// </summary>

        public object Value

        {

            get { return this.value; }

        }



        private void Attach()

        {

            this.Detach();



            if (this.target != null && this.binding != null)

            {

                this.listener = this.GetListener();

                this.listener.Attach(this.target, this.binding);

            }

        }



        private void Detach()

        {

            if (this.listener != null)

            {

                this.ReturnListener();

            }

        }



        private DependencyPropertyListener GetListener()

        {

            DependencyPropertyListener dependencyPropertyListener;



            if (freeListeners.Count != 0)

            {

                dependencyPropertyListener = freeListeners[freeListeners.Count - 1];

                freeListeners.RemoveAt(freeListeners.Count - 1);



                return dependencyPropertyListener;

            }

            else

            {

                dependencyPropertyListener = new DependencyPropertyListener();

            }



            dependencyPropertyListener.Changed += this.HandleValueChanged;



            return dependencyPropertyListener;

        }



        private void HandleValueChanged(object sender, BindingChangedEventArgs e)

        {

            this.value = e.EventArgs.NewValue;



            this.changedHandler(this, e);

        }



        private void ReturnListener()

        {

            this.listener.Changed -= this.HandleValueChanged;



            freeListeners.Add(this.listener);



            this.listener = null;

        }

    }

}