Estoy creando un cuadro combinado de selección múltiple en Windows 8 como se muestra en la siguiente imagen:

Para ello, he creado un código de control personalizado para el que se menciona a continuación: El problema con el siguiente código es que 1. al seleccionar todos los elementos no están seleccionados 2. Los elementos seleccionados no se muestran en el cuadro de texto

Cómo puedo arreglar eso. ¿Necesita ayuda lo antes posible por favor

XAML:

<UserControl
    x:Class="App5.MultiSelectComboBox"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App5"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300"
    x:Name="thisUC"
    d:DesignWidth="400">

        <ComboBox
        x:Name="MultiSelectCombo"  
        ScrollViewer.HorizontalScrollBarVisibility="Auto"
        ScrollViewer.VerticalScrollBarVisibility="Auto"
Width="400" Height="20" 
                           >
        <ComboBox.ItemTemplate>
            <DataTemplate>
                <CheckBox Content="{Binding Title}" Foreground="Black"
                          IsChecked="{Binding ElementName=thisUC, Path=IsSelected, Mode=TwoWay}"
                           Click="CheckBox_Click" />
            </DataTemplate>
        </ComboBox.ItemTemplate>
        <ControlTemplate TargetType="ComboBox">
            <Grid >
                <ToggleButton 
                        x:Name="ToggleButton" 
                       Grid.Column="2" IsChecked="{TemplateBinding IsDropDownOpen}"

                        ClickMode="Press" HorizontalContentAlignment="Left" >
                    <ToggleButton.Template>
                        <ControlTemplate>
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="*"/>
                                    <ColumnDefinition Width="18"/>
                                </Grid.ColumnDefinitions>
                                <Border
                  x:Name="Border" 
                  Grid.ColumnSpan="2"
                  CornerRadius="2"
                  Background="White"
                  BorderBrush="Black"
                  BorderThickness="1,1,1,1" />
                                <Border 
                    x:Name="BorderComp" 
                  Grid.Column="0"
                  CornerRadius="2" 
                  Margin="1" 
                 Background="White"
                  BorderBrush="Black"
                  BorderThickness="0,0,0,0" >
                                    <TextBlock Foreground="Black" Text="{TemplateBinding TextValue}" 
                            Padding="3" />
                                </Border>
                                <Path 
                  x:Name="Arrow"
                  Grid.Column="1"     
                  Fill="Black"
                  HorizontalAlignment="Center"
                  VerticalAlignment="Center"
                  Data="M 0 0 L 4 4 L 8 0 Z"/>
                            </Grid>
                        </ControlTemplate>
                    </ToggleButton.Template>
                </ToggleButton>
                <Popup 
                        Name="Popup"
                         IsOpen="{TemplateBinding IsDropDownOpen}"
                        >
                    <Grid 
                        Name="DropDown"
                        MinWidth="{TemplateBinding ActualWidth}"
                        MaxHeight="{TemplateBinding MaxDropDownHeight}">
                        <Border x:Name="DropDownBorder"
                                   BorderThickness="1" Background="White"
                                    BorderBrush="Black"/>
                        <ScrollViewer Margin="4,6,4,6" DataContext="{Binding}">
                            <StackPanel  />
                        </ScrollViewer>
                    </Grid>
                </Popup>
            </Grid>
            <!--<ControlTemplate.Triggers>
                    <Trigger Property="HasItems" Value="false">
                        <Setter TargetName="DropDownBorder" Property="MinHeight" Value="95"/>
                    </Trigger>
                    <Trigger SourceName="Popup" Property="Popup.AllowsTransparency" Value="true">
                        <Setter TargetName="DropDownBorder" Property="CornerRadius" Value="4"/>
                        <Setter TargetName="DropDownBorder" Property="Margin" Value="0,2,0,0"/>
                    </Trigger>
                </ControlTemplate.Triggers>-->
        </ControlTemplate>

    </ComboBox>
</UserControl>

DO#

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.IO;
using System.Linq;
using System.Text;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

// The User Control item template is documented at http://go.microsoft.com/fwlink/?LinkId=234236

namespace App5
{
    public sealed partial class MultiSelectComboBox : UserControl
    {
        private ObservableCollection<Node> _nodeList;
        public MultiSelectComboBox()
        {
            InitializeComponent();
            _nodeList = new ObservableCollection<Node>();
        }

        #region Dependency Properties

        public static readonly DependencyProperty ItemsSourceProperty =
             DependencyProperty.Register("ItemsSource", typeof(Dictionary<string, object>), typeof(MultiSelectComboBox), new PropertyMetadata(null,
        new PropertyChangedCallback(MultiSelectComboBox.OnItemsSourceChanged)));

        public static readonly DependencyProperty SelectedItemsProperty =
         DependencyProperty.Register("SelectedItems", typeof(Dictionary<string, object>), typeof(MultiSelectComboBox), new PropertyMetadata(null,
     new PropertyChangedCallback(MultiSelectComboBox.OnSelectedItemsChanged)));

        public static readonly DependencyProperty TextProperty =
           DependencyProperty.Register("TextValue", typeof(string), typeof(MultiSelectComboBox), new PropertyMetadata(null));

        public static readonly DependencyProperty DefaultTextProperty =
            DependencyProperty.Register("DefaultText", typeof(string), typeof(MultiSelectComboBox), new PropertyMetadata(null));



        public Dictionary<string, object> ItemsSource
        {
            get { return (Dictionary<string, object>)GetValue(ItemsSourceProperty); }
            set
            {
                SetValue(ItemsSourceProperty, value);
            }
        }

        public Dictionary<string, object> SelectedItems
        {
            get { return (Dictionary<string, object>)GetValue(SelectedItemsProperty); }
            set
            {
                SetValue(SelectedItemsProperty, value);
            }
        }

        public string TextValue
        {
            get { return (string)GetValue(TextProperty); }
            set { SetValue(TextProperty, value); }
        }

        public string DefaultText
        {
            get { return (string)GetValue(DefaultTextProperty); }
            set { SetValue(DefaultTextProperty, value); }
        }
        #endregion

        #region Events
        private static void OnItemsSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            MultiSelectComboBox control = (MultiSelectComboBox)d;
            control.DisplayInControl();
        }

        private static void OnSelectedItemsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            MultiSelectComboBox control = (MultiSelectComboBox)d;
            control.SelectNodes();
            control.SetText();
        }

        private void CheckBox_Click(object sender, RoutedEventArgs e)
        {
            CheckBox clickedBox = (CheckBox)sender;

            if (clickedBox.Content == "All")
            {
                if (clickedBox.IsChecked.Value)
                {
                    foreach (Node node in _nodeList)
                    {
                        node.IsSelected = true;
                    }
                }
                else
                {
                    foreach (Node node in _nodeList)
                    {
                        node.IsSelected = false;
                    }
                }

            }
            else
            {
                int _selectedCount = 0;
                foreach (Node s in _nodeList)
                {
                    if (s.IsSelected && s.Title != "All")
                        _selectedCount++;
                }
                if (_selectedCount == _nodeList.Count - 1)
                    _nodeList.FirstOrDefault(i => i.Title == "All").IsSelected = true;
                else
                    _nodeList.FirstOrDefault(i => i.Title == "All").IsSelected = false;
            }
            SetSelectedItems();
            SetText();

        }
        #endregion


        #region Methods
        private void SelectNodes()
        {
            foreach (KeyValuePair<string, object> keyValue in SelectedItems)
            {
                Node node = _nodeList.FirstOrDefault(i => i.Title == keyValue.Key);
                if (node != null)
                    node.IsSelected = true;
            }
        }

        private void SetSelectedItems()
        {
            if (SelectedItems == null)
                SelectedItems = new Dictionary<string, object>();
            SelectedItems.Clear();
            foreach (Node node in _nodeList)
            {
                if (node.IsSelected && node.Title != "All")
                {
                    if (this.ItemsSource.Count > 0)

                        SelectedItems.Add(node.Title, this.ItemsSource[node.Title]);
                }
            }
        }

        private void DisplayInControl()
        {
            _nodeList.Clear();
            if (this.ItemsSource.Count > 0)
                _nodeList.Add(new Node("All"));
            foreach (KeyValuePair<string, object> keyValue in this.ItemsSource)
            {
                Node node = new Node(keyValue.Key);
                _nodeList.Add(node);
            }

            MultiSelectCombo.ItemsSource = _nodeList;
        }

        private void SetText()
        {
            if (this.SelectedItems != null)
            {
                StringBuilder displayText = new StringBuilder();
                foreach (Node s in _nodeList)
                {
                    if (s.IsSelected == true && s.Title == "All")
                    {
                        displayText = new StringBuilder();
                        displayText.Append("All");
                        break;
                    }
                    else if (s.IsSelected == true && s.Title != "All")
                    {
                        displayText.Append(s.Title);
                        displayText.Append(',');
                    }
                }
                this.TextValue = displayText.ToString().TrimEnd(new char[] { ',' });
            }
            // set DefaultText if nothing else selected
            if (string.IsNullOrEmpty(this.TextValue))
            {
                this.TextValue = this.DefaultText;
            }
        }


        #endregion
    }

    public class Node : INotifyPropertyChanged
    {

        private string _title;
        private bool _isSelected;
        #region ctor
        public Node(string title)
        {
            Title = title;
        }
        #endregion

        #region Properties
        public string Title
        {
            get
            {
                return _title;
            }
            set
            {
                _title = value;
                NotifyPropertyChanged("Title");
            }
        }
        public bool IsSelected
        {
            get
            {
                return _isSelected;
            }
            set
            {
                _isSelected = value;
                NotifyPropertyChanged("IsSelected");
            }
        }
        #endregion

        public event PropertyChangedEventHandler PropertyChanged;
        protected void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

    }
}