Semantic Zoom - Show letters containing no items

Question

How can I show letters of the alphabet, which contain no items beginning with that letter (in gray) within the ZoomedOutView view of my semantic zoom control?
I want to achieve something like this (excluding 'Social', 'Favorites' and '#'): 
but I end up with this:
MetropolitanDataSource.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace EELL
using System;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Media;
// To significantly reduce the sample data footprint in your production application, you can set
// the DISABLE_SAMPLE_DATA conditional compilation constant and disable sample data at runtime.
#if DISABLE_SAMPLE_DATA
internal class SampleDataSource { }
#else
public class Item : System.ComponentModel.INotifyPropertyChanged
public event System.ComponentModel.PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
if (this.PropertyChanged != null)
this.PropertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs(propertyName));
private string _Station = string.Empty;
public string Station
get
return this._Station;
set
if (this._Station != value)
this._Station = value;
this.OnPropertyChanged("Station");
private string _Zone = string.Empty;
public string Zone
get
return this._Zone;
set
if (this._Zone != value)
this._Zone = value;
this.OnPropertyChanged("Zone");
private string _Link = string.Empty;
public string Link
get
return this._Link;
set
if (this._Link != value)
this._Link = value;
this.OnPropertyChanged("Link");
public class GroupInfoList<T> : List<object>
public object Key { get; set; }
public new IEnumerator<object> GetEnumerator()
return (System.Collections.Generic.IEnumerator<object>)base.GetEnumerator();
public class StoreData
public StoreData()
Item item;
item = new Item();
item.Station = "Aldgate";
item.Link = "/Lines and Stations/Metropolitan/Aldgate_(Metropolitan).xaml";
Collection.Add(item);
item = new Item();
item.Station = "Moorgate";
item.Link = "/Lines and Stations/Metropolitan/MOG_(Metropolitan).xaml";
Collection.Add(item);
private ItemCollection _Collection = new ItemCollection();
public ItemCollection Collection
get
return this._Collection;
internal List<GroupInfoList<object>> GetGroupsByCategory()
List<GroupInfoList<object>> groups = new List<GroupInfoList<object>>();
var query = from item in Collection
orderby ((Item)item).Zone
group item by ((Item)item).Zone into g
select new { GroupName = g.Key, Items = g };
foreach (var g in query)
GroupInfoList<object> info = new GroupInfoList<object>();
info.Key = g.GroupName;
foreach (var item in g.Items)
info.Add(item);
groups.Add(info);
return groups;
internal List<GroupInfoList<object>> GetGroupsByLetter()
List<GroupInfoList<object>> groups = new List<GroupInfoList<object>>();
var query = from item in Collection
orderby ((Item)item).Station
group item by ((Item)item).Station[0] into g
select new { GroupName = g.Key, Items = g };
foreach (var g in query)
GroupInfoList<object> info = new GroupInfoList<object>();
info.Key = g.GroupName;
foreach (var item in g.Items)
info.Add(item);
groups.Add(info);
return groups;
// Workaround: data binding works best with an enumeration of objects that does not implement IList
public class ItemCollection : IEnumerable<Object>
private System.Collections.ObjectModel.ObservableCollection<Item> itemCollection = new System.Collections.ObjectModel.ObservableCollection<Item>();
public IEnumerator<Object> GetEnumerator()
return itemCollection.GetEnumerator();
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
return GetEnumerator();
public void Add(Item item)
itemCollection.Add(item);
#endif
Metropolitan_line.xaml.cs
using Exits_Expert_London_Lite.Common;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
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 Basic Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234237
namespace Exits_Expert_London_Lite.Lines_and_Stations.Metropolitan
/// <summary>
/// An empty page that can be used on its own or navigated to within a Frame.
/// </summary>
public sealed partial class Metropolitan_line : Page
public Metropolitan_line()
this.InitializeComponent();
StoreData _storeData = null;
// creates a new instance of the sample data
_storeData = new StoreData();
// sets the list of categories to the groups from the sample data
List<GroupInfoList<object>> dataLetter = _storeData.GetGroupsByLetter();
// sets the CollectionViewSource in the XAML page resources to the data groups
cvs2.Source = dataLetter;
// sets the items source for the zoomed out view to the group data as well
(semanticZoom.ZoomedOutView as ListViewBase).ItemsSource = cvs2.View.CollectionGroups;
#region Data Visualization
/// <summary>
/// We will visualize the data item in asynchronously in multiple phases for improved panning user experience
/// of large lists. In this sample scneario, we will visualize different parts of the data item
/// in the following order:
/// 1) Placeholders (visualized synchronously - Phase 0)
/// 2) Tilte (visualized asynchronously - Phase 1)
/// 3) Image (visualized asynchronously - Phase 2)
/// </summary>
/// <param name="sender"></param>
/// <param name="args"></param>
void ItemsGridView_ContainerContentChanging(ListViewBase sender, ContainerContentChangingEventArgs args)
ItemViewer iv = args.ItemContainer.ContentTemplateRoot as ItemViewer;
if (args.InRecycleQueue == true)
iv.ClearData();
else if (args.Phase == 0)
iv.ShowPlaceholder(args.Item as Item);
// Register for async callback to visualize Title asynchronously
args.RegisterUpdateCallback(ContainerContentChangingDelegate);
else if (args.Phase == 1)
iv.ShowStation();
args.RegisterUpdateCallback(ContainerContentChangingDelegate);
else if (args.Phase == 2)
iv.ShowZone();
// For imporved performance, set Handled to true since app is visualizing the data item
args.Handled = true;
/// <summary>
/// Managing delegate creation to ensure we instantiate a single instance for
/// optimal performance.
/// </summary>
private TypedEventHandler<ListViewBase, ContainerContentChangingEventArgs> ContainerContentChangingDelegate
get
if (_delegate == null)
_delegate = new TypedEventHandler<ListViewBase, ContainerContentChangingEventArgs>(ItemsGridView_ContainerContentChanging);
return _delegate;
private TypedEventHandler<ListViewBase, ContainerContentChangingEventArgs> _delegate;
#endregion //Data Visualization

Answer 1

Yes, it only shows the letters that contain children items.
Please have a look at my code snippet below and tell me what needs to change:
internal List<GroupInfoList<object>> GetGroupsByLetter()
var letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToList();
var groupByAlphabets = from letter in letters
select new
Key = letter,
Items = (from item in Collection
where ((Item)item).Station.StartsWith(letter.ToString(), StringComparison.CurrentCultureIgnoreCase)
orderby ((Item)item).Station
group item by ((Item)item).Station[0] into g
select g)
List<GroupInfoList<object>> groups = new List<GroupInfoList<object>>();
foreach (var g in groupByAlphabets)
GroupInfoList<object> info = new GroupInfoList<object>();
info.Key = g.Key;
foreach (var item in g.Items)
info.Add(item);
groups.Add(info);
return groups;