WPF M-V-VM: получить выбранные элементы из ListCollectionView?

Эталонная реализация PRISM MVVM имеет поведение, называемое SynchronizeSelectedItems, используемое в Prism4\MVVM RI\MVVM.Клиент\Представления \ MultipleSelectionView.xaml, который синхронизирует проверяемые элементы со свойством ViewModel с именем Selections:

        <ListBox Grid.Column="0" Grid.Row="1" IsTabStop="False" SelectionMode="Multiple"
                 ItemsSource="{Binding Question.Range}" Margin="5">

            <ListBox.ItemContainerStyle>
                <!-- Custom style to show the multi-selection list box as a collection of check boxes -->
                <Style TargetType="ListBoxItem">
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="ListBoxItem">
                                <Grid Background="Transparent">
                                    <CheckBox IsChecked="{Binding IsSelected, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}" 
                                              IsHitTestVisible="False" IsTabStop="True"
                                              AutomationProperties.AutomationId="CheckBoxAutomationId">
                                        <ContentPresenter/>
                                    </CheckBox>
                                </Grid>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </ListBox.ItemContainerStyle>
            <i:Interaction.Behaviors>
                <!-- Custom behavior that synchronizes the selected items with the view models collection -->
                <Behaviors:SynchronizeSelectedItems Selections="{Binding Selections}"/>
            </i:Interaction.Behaviors>
        </ListBox>

Перейти к http://compositewpf.codeplex.com/ и захватить все это или использовать это:

//===================================================================================
// 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;
                }
            }
        }
    }
}