Binding to an ObservableCollection to show the first X number of C # WPF elements

Question

Background designation

Ok that's why i bind ContextMenu ItemsSourceto ObservableCollectionfrom letTypeA

The following code is inside a singleton DataStore class

private ObservableCollection<TypeA> TypeACollection = new ObservableCollection<TypeA>();

public ObservableCollection<TypeA> GetTypeACollection
{
    get { return TypeACollection; }
}
public ObservableCollection<TypeA> GetFirstFiveTypeACollection
{
    get 
    {
        return TypeACollection.Take(5);
    }
}

Now I have successfully linked ItemsControlto GetTypeACollectionwith the following XAML code:

The following code is inside MainWindow.xaml

<ItemsControl x:Name="TypeAList" ItemsSource="{Binding GetTypeACollection, Source={StaticResource DataStore}, UpdateSourceTrigger=PropertyChanged}" >
<ItemsControl.ItemsPanel>
    <ItemsPanelTemplate>
        <VirtualizingStackPanel />
    </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <User_Controls:TypeAUserControl Type="{Binding }"/>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

This works as expected, showing TypeAUserControlcorrectly formatted, as expected, data fromTypeA

Now, when I try to repeat this on ContextMenu MenuItem, binding ItemsSourceto GetFirstFiveTypeACollection, I first see the expected results, however, when the object TypeAis deleted, MainWindow is updated ItemsControl, where ContextMenuthere is none.

, , ContextMenu "" ObservableCollection<TypeA> ( GetFirstFiveTypeAColletion).

IValueConverter

ValueConverters

public class ObservableCollectionTypeAResizeConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        ObservableCollection<TypeA> TypeACollection = value as ObservableCollection<TypeA>;

        return TypeACollection.Take(System.Convert.ToInt32(parameter));
    }
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return null;
    }
}

XAML, .

IValueConverter

<MenuItem Header="First 5 Type A" Name="MI_FirstFiveTypeA" 
    ItemsSource="{Binding DATA_STORE.GetTypeACollection, ConverterParameter=5,
            Converter={StaticResource ObservableCollectionTypeAResizeConverter}, 
            Source={StaticResource DataStore}}" 
/>

GetFirstFiveTypeACollection

<MenuItem Header="First 5 Type A" Name="MI_FirstFiveTypeA" 
    ItemsSource="{Binding DATA_STORE.RecentTimers, Source={StaticResource DataStore}, 
            UpdateSourceTrigger=PropertyChanged}"
/>

, , !

,

DataStore.cs

private ObservableCollection<TimerType> TimerTypes = new ObservableCollection<TimerType>();

public ObservableCollection<TimerType> getTimerTypes
{
    get 
    { 
        return new ObservableCollection<TimerType>(TimerTypes.OrderByDescending(t => t.LastUsed)); 
    }
}
public ObservableCollection<TimerType> RecentTimers
{
    get 
    { 
        return new ObservableCollection<TimerType>(TimerTypes.OrderByDescending(t => t.LastUsed).Take(5)); 
    }
}

public event PropertyChangedEventHandler PropertyChanged;

// Create the OnPropertyChanged method to raise the event
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
    if (PropertyChanged != null)
    {
        PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}
//THIS IS IN THE ADD METHOD
TimerTypes.Add(timer);
NotifyPropertyChanged("getTimerTypes");
NotifyPropertyChanged("RecentTimers");
NotifyPropertyChanged("TimerTypes");

//THIS IS IN THE REMOVE METHOD
TimerTypes.Remove(Timer);
NotifyPropertyChanged("getTimerTypes");
NotifyPropertyChanged("RecentTimers");
NotifyPropertyChanged("TimerTypes");

MainWindow.xaml

<ItemsControl x:Name="TimersList" ItemsSource="{Binding Path=getTimerTypes, UpdateSourceTrigger=PropertyChanged}" >

MainWindow.xaml.cs

//Lists are populated in DataStore.cs before this.
DataContext = DataStore.DATA_STORE;
InitializeComponent();

NotifyIcon.xaml

<MenuItem Header="Recent Timers" Name="MIRecent" ItemsSource="{Binding RecentTimers, UpdateSourceTrigger=PropertyChanged}"/>

NotifyIcon.xaml.cs

DataContext = DataStore.DATA_STORE;
InitializeComponent();

, , a TimerType , PropertyChangedEventHandler NULL. , DataContext, , DataContext Bindings?

Singleton

private static readonly DataStore Instance = new DataStore();

private DataStore() { }

public static DataStore DATA_STORE
{
    get { return Instance; }
    set { }
}

Answer 1

, Take ( LINQ), IEnumerable . , INotifyCollectionChanged, .

- INotifyCollectionChanged. PropertyChanged "", / , IEnumerable.

Answer 2

, CollectionView

public class MyViewModel
{
    CollectionView _mostRecentDocuments;

    public MyViewModel()
    {
        Documents = new ObservableCollection<Document>();
        _mostRecentDocuments = new CollectionView(Documents);
        _mostRecentDocuments .Filter = x => Documents.Take(5).Contains(x);
    }

    public ObservableCollection<Document> Documents { get; private set; }    

    public CollectionView MostRecentDocuments
    {
        get 
        {
            return _mostRecentDocuments;
        }
    }
}