/V4/MVVM RI/MVVM.Client/Infrastructure/Behaviors/SynchronizeSelectedItems.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.Collections;

using System.Collections.Specialized;

using System.Diagnostics.CodeAnalysis;

using System.Windows;

using System.Windows.Controls;

using System.Windows.Interactivity;



namespace MVVM.Client.Infrastructure.Behaviors

{

    /// <summary>

    /// Custom behavior that synchronizes the list in <see cref="ListBox.SelectedItems"/> with a collection.

    /// </summary>

    /// <remarks>

    /// This behavior uses a weak event handler to listen for changes on the synchronized collection.

    /// </remarks>

    public class SynchronizeSelectedItems : Behavior<ListBox>

    {

        public static readonly DependencyProperty SelectionsProperty =

            DependencyProperty.Register(

                "Selections",

                typeof(IList),

                typeof(SynchronizeSelectedItems),

                new PropertyMetadata(null, OnSelectionsPropertyChanged));



        private bool updating;

        private WeakEventHandler<SynchronizeSelectedItems, object, NotifyCollectionChangedEventArgs> currentWeakHandler;



        [SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly",

            Justification = "Dependency property")]

        public IList Selections

        {

            get { return (IList)this.GetValue(SelectionsProperty); }

            set { this.SetValue(SelectionsProperty, value); }

        }



        protected override void OnAttached()

        {

            base.OnAttached();



            this.AssociatedObject.SelectionChanged += this.OnSelectedItemsChanged;

            this.UpdateSelectedItems();

        }



        protected override void OnDetaching()

        {

            this.AssociatedObject.SelectionChanged += this.OnSelectedItemsChanged;



            base.OnDetaching();

        }



        private static void OnSelectionsPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)

        {

            var behavior = d as SynchronizeSelectedItems;



            if (behavior != null)

            {

                if (behavior.currentWeakHandler != null)

                {

                    behavior.currentWeakHandler.Detach();

                    behavior.currentWeakHandler = null;

                }



                if (e.NewValue != null)

                {

                    var notifyCollectionChanged = e.NewValue as INotifyCollectionChanged;

                    if (notifyCollectionChanged != null)

                    {

                        behavior.currentWeakHandler =

                            new WeakEventHandler<SynchronizeSelectedItems, object, NotifyCollectionChangedEventArgs>(

                                behavior,

                                (instance, sender, args) => instance.OnSelectionsCollectionChanged(sender, args),

                                (listener) => notifyCollectionChanged.CollectionChanged -= listener.OnEvent);

                        notifyCollectionChanged.CollectionChanged += behavior.currentWeakHandler.OnEvent;

                    }



                    behavior.UpdateSelectedItems();

                }

            }

        }



        private void OnSelectedItemsChanged(object sender, SelectionChangedEventArgs e)

        {

            this.UpdateSelections(e);

        }



        private void UpdateSelections(SelectionChangedEventArgs e)

        {

            this.ExecuteIfNotUpdating(

                () =>

                {

                    if (this.Selections != null)

                    {

                        foreach (var item in e.AddedItems)

                        {

                            this.Selections.Add(item);

                        }



                        foreach (var item in e.RemovedItems)

                        {

                            this.Selections.Remove(item);

                        }

                    }

                });

        }



        private void OnSelectionsCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)

        {

            this.UpdateSelectedItems();

        }



        private void UpdateSelectedItems()

        {

            this.ExecuteIfNotUpdating(

                () =>

                {

                    if (this.AssociatedObject != null)

                    {

                        this.AssociatedObject.SelectedItems.Clear();

                        foreach (var item in this.Selections ?? new object[0])

                        {

                            this.AssociatedObject.SelectedItems.Add(item);

                        }

                    }

                });

        }



        private void ExecuteIfNotUpdating(Action execute)

        {

            if (!this.updating)

            {

                try

                {

                    this.updating = true;

                    execute();

                }

                finally

                {

                    this.updating = false;

                }

            }

        }

    }

}