¿Cómo se vincula un CollectionContainer a una colección en un modelo de vista?

Question

Tengo un modelo de vista con una propiedad que expone una colección de cosas. Tengo un ComboBox cuya propiedad ItemsSource está vinculada a esta colección. Ahora el usuario puede seleccionar de la lista.

Quiero permitir que el usuario borre la selección, así que quiero agregar un elemento (que sea nulo) a ComboBox. Es bastante sencillo.

Decidí probar y usar CompositeCollection para ItemsSource para poder agregar los elementos en la lista existente al ComboBox así como también el elemento Null extra.

Después de luchar con esto por un tiempo, decidí volver a la documentación en el CompositeCollection Class. Copié su ejemplo y lo modifiqué para usar un modelo de vista en lugar de recursos estáticos.

Descubrí que no aparecen elementos en la lista cuando vinculo el CollectionContainer a la lista expuesta por ViewModel.

No estoy seguro de cómo solucionar este problema y estoy buscando algún consejo sobre este tema.

Aquí está mi código XAML:

<Window Background="CornflowerBlue" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:c="clr-namespace:TryingWPF" x:Class="CompositeCollections" Title="CompositeCollections" SizeToContent="WidthAndHeight"> 
<Window.Resources> 
    <c:CompositeCollectionVM x:Key="CompositeCollectionVM"/> 
    <XmlDataProvider x:Key="GreekHeroesData" XPath="GreekHeroes/Hero"> 
     <x:XData> 
      <GreekHeroes xmlns=""> 
       <Hero Name="Jason" /> 
       <Hero Name="Hercules" /> 
       <Hero Name="Bellerophon" /> 
       <Hero Name="Theseus" /> 
       <Hero Name="Odysseus" /> 
       <Hero Name="Perseus" /> 
      </GreekHeroes> 
     </x:XData> 
    </XmlDataProvider> 
    <DataTemplate DataType="{x:Type c:GreekGod}"> 
     <TextBlock Text="{Binding Path=Name}" Foreground="Gold"/> 
    </DataTemplate> 
    <DataTemplate DataType="Hero"> 
     <TextBlock Text="{Binding XPath=@Name}" Foreground="Cyan"/> 
    </DataTemplate> 
</Window.Resources> 

<StackPanel DataContext="{StaticResource CompositeCollectionVM}"> 
    <TextBlock FontSize="18" FontWeight="Bold" Margin="10" HorizontalAlignment="Center" Foreground="WhiteSmoke">Trying Composite Collections</TextBlock> 
    <DockPanel> 
     <ListBox Name="myListBox" Height="300" Background="#99333333"> 
      <ListBox.ItemsSource> 
       <CompositeCollection> 
        <CollectionContainer Collection="{Binding GreekGods}" /> 
        <CollectionContainer Collection="{Binding Source={StaticResource GreekHeroesData}}" /> 
        <ListBoxItem Foreground="Magenta">Other Listbox Item 1</ListBoxItem> 
        <ListBoxItem Foreground="Magenta">Other Listbox Item 2</ListBoxItem> 
       </CompositeCollection> 
      </ListBox.ItemsSource> 
     </ListBox> 
     <ListBox ItemsSource="{Binding GreekGods}" Background="#99333333" Margin="5,0" HorizontalAlignment="Right"> 
     </ListBox> 
    </DockPanel> 
</StackPanel> 
</Window> 

(Como se puede ver cuando me ato la ItemsSource del segundo cuadro de lista a la propiedad de lista ... los artículos aparecen)

Y aquí está mi código VB.NET que hace funcionar el código XAML:

Public Class CompositeCollections 
End Class 

Public Class GreekGod 
    Public Property GreekName 
    Public Property Name 
    Public Property Description 
    Public Sub New(ByVal greekName As String, ByVal englishName As String, ByVal description As String) 
     Me.GreekName = greekName 
     Me.Name = englishName 
     Me.Description = description 
    End Sub 
End Class 

Public Class CompositeCollectionVM 
    Public Property GreekGods As System.Collections.ObjectModel.ObservableCollection(Of GreekGod) 
    Public Sub New() 
     GreekGods = New System.Collections.ObjectModel.ObservableCollection(Of GreekGod) 

     GreekGods.Add(New GreekGod("Ἀφροδίτη (Venus)", "Aphrodite", "Goddess of love and beauty. Although married to Hephaestus she had many lovers, most notably Ares. She was depicted as a beautiful woman usually accompanied by her son Eros. Her symbols include the rose, scallop shell, and myrtle wreath. Her sacred animal is the dove.")) 
     GreekGods.Add(New GreekGod("Ἀπόλλων (Apóllō)", "Apollo", "God of music, healing, plague, prophecies, poetry, and archery; associated with light, truth and the sun. He is Artemis's twin brother and Hermes elder brother, and son of Zeus and Leto. He was depicted as a handsome, beardless youth with long hair and various attributes including a laurel wreath, bow and quiver, raven, and lyre. Apollo's sacred animal are red cattle.")) 
     GreekGods.Add(New GreekGod("Ἄρης (Mars)", "Ares", "God of war, bloodlust, violence, manly courage, and civil order. The son of Zeus and Hera, he was depicted as either a mature, bearded warrior dressed in battle arms, or a nude beardless youth with helm and spear. His attributes are golden armour and a bronze-tipped spear. His sacred animals are the vulture, venomous snakes, alligators, and dogs.")) 
     GreekGods.Add(New GreekGod("Ἄρτεμις (Diana)", "Artemis", "Virgin goddess of the hunt, wilderness, wild animals, childbirth and plague. In later times she became associated with the moon. She is the daughter of Zeus and Leto, and twin sister of Apollo. In art she was usually depicted as a young woman dressed in a short knee-length chiton and equipped with a hunting bow and a quiver of arrows. In addition to the bow, her attributes include hunting spears, animal pelts, deer and other wild animals. Her sacred animals are deer, bears, and wild boars.")) 
     GreekGods.Add(New GreekGod("Ἀθηνᾶ (Minerva)", "Athena", "Goddess of wisdom, warfare, battle strategy, heroic endeavour, handicrafts and reason. According to most traditions she was born from Zeus's head. She was depicted crowned with a crested helm, armed with shield (Aegis), which holds medusa's head to paralyze her enemies who looked at it and a spear. Her symbols include the aegis and the olive tree. She is commonly shown accompanied by her sacred animal, the snowy owl.")) 
     GreekGods.Add(New GreekGod("Δημήτηρ (Ceres)", "Demeter", "Goddess of agriculture, horticulture, grain and harvest. Demeter is a daughter of Cronus and Rhea and sister of Zeus, by whom she bore Persephone. She was depicted as a mature woman, often crowned and holding sheafs of wheat and a torch. Her symbols are the Cornucopia (horn of plenty), wheat-ears, the winged serpent and the lotus staff. Her sacred animals are pigs and snakes.")) 
     GreekGods.Add(New GreekGod("Διόνυσος (Bacchus)", "Dionysos", "God of wine, parties and festivals, madness, civilization, drunkenness and pleasure at forever young. He was depicted in art as either an older bearded god or a pretty effeminate, long-haired youth. His attributes include the thyrsus (a pinecone-tipped staff), drinking cup, grape vine, and a crown of ivy. Animals sacred to him include dolphins, serpents, tigers, panthers, and donkeys. A later addition to the Olympians, in some accounts he replaced Hestia.")) 
     GreekGods.Add(New GreekGod("ᾍδης (Hádēs) or Πλούτων (Ploútón)", "Hades or Pluto", "King of the Underworld and god of the dead and the hidden wealth of the Earth. His consort is Persephone and his attributes are the key of Hades, the Helm of Darkness, and the three-headed dog, Cerberus. The screech owl was sacred to him. Despite being the son of Cronus and Rhea and the elder brother of Zeus, as a chthonic god he is only rarely listed among the Olympians. The name Pluto became more common in the Classical period with the mystery religions and Athenian literature.")) 
     GreekGods.Add(New GreekGod("Ἥφαιστος (Hḗphaistos)", "Hephaestus or Vulcan", "Crippled god of fire, metalworking, stonemasonry, sculpture and volcanism. The son of Hera alone, he is the smith of the gods and the husband of the adulterous Aphrodite. He was usually depicted as a bearded man holding hammer and tongs—the tools of a smith—and riding a donkey. His symbols are the hammer, tongs, and anvil. His sacred animals are the donkey, the guard dog and the crane. When he was born, he was thrown off of Mount Olympus by Hera as he was considered ugly.")) 
     GreekGods.Add(New GreekGod("Ἥρα (Juno)", "Hera", "Queen of marriage, women, childbirth, heirs, kings and empires. She is daughter of Cronus and Rhea. She was usually depicted as a beautiful woman wearing a crown and veil and holding a royal, lotus-tipped staff. Her sacred animals are the cow, the peacock. She is the eternal wife of Zeus.")) 
     GreekGods.Add(New GreekGod("Ἡρμῆς (Mercury)", "Hermes", "God of travel, messengers, trade, thievery, cunning wiles, language, writing, diplomacy, athletics, and animal husbandry. He is the messenger of the gods, a psychopomp who leads the souls of the dead into Hades' realm, and the son of Zeus and Maia. He was depicted either as a handsome and athletic beardless youth, or as an older bearded man. His attributes include the herald's wand or caduceus, winged sandals, and a traveler's cap. His sacred animals are the tortoise, the ram, and the hawk.")) 
     GreekGods.Add(New GreekGod("Ἑστία (Vesta)", "Hestia", "Virgin goddess of the hearth, home and cooking. She is a daughter of Rhea and Cronus and sister of Zeus. She was depicted as a modestly veiled woman, whose symbols are the hearth and kettle. In some accounts, she gave up her seat as one of the Twelve Olympians to tend to the sacred flame on Mount Olympus for Dionysus.")) 
     GreekGods.Add(New GreekGod("Ποσειδῶν (Neptune)", "Poseidon", "God of the sea, rivers, floods, droughts, storms, earthquakes, and the creator of horses; known as the 'Earth Shaker' or 'Storm Bringer'. He is a son of Cronus and Rhea and brother to Zeus and Hades. In classical artwork, he was depicted as a mature man of sturdy build with a dark beard, and holding a trident. The horse and the dolphin are sacred to him.")) 
     GreekGods.Add(New GreekGod("Ζεύς (Jupiter)", "Zeus", "The king of the gods, the ruler of Mount Olympus and the god of the sky, weather, thunder, law, order, and fate. He is the youngest son of Cronus and Rhea, whom he overthrew after Cronus swallowed his brothers and sisters and he is brother-husband to Hera. In artwork, he was depicted as a regal, mature man with a sturdy figure and dark beard. His usual attributes are the royal sceptre and the lightning bolt. His main attribute was his master bolt. His sacred animals are the eagle and the bull.")) 


    End Sub 
End Class 

Gracias por su ayuda!

EDIT:

respuesta de H. B. funcionó a la perfección. Aquí está el XAML actualizado de trabajo:

<Window Background="CornflowerBlue" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:c="clr-namespace:TryingWPF" 
    x:Class="CompositeCollections" 
    Title="CompositeCollections" 
    SizeToContent="WidthAndHeight"> 
    <Window.Resources> 
     <c:CompositeCollectionVM x:Key="CompositeCollectionVM"/> 
     <XmlDataProvider x:Key="GreekHeroesData" XPath="GreekHeroes/Hero"> 
      <x:XData> 
       <GreekHeroes xmlns=""> 
        <Hero Name="Jason" /> 
        <Hero Name="Hercules" /> 
        <Hero Name="Bellerophon" /> 
        <Hero Name="Theseus" /> 
        <Hero Name="Odysseus" /> 
        <Hero Name="Perseus" /> 
       </GreekHeroes> 
      </x:XData> 
     </XmlDataProvider> 
     <DataTemplate DataType="{x:Type c:GreekGod}"> 
      <TextBlock Text="{Binding Path=Name}" Foreground="Gold"/> 
     </DataTemplate> 
     <DataTemplate DataType="Hero"> 
      <TextBlock Text="{Binding XPath=@Name}" Foreground="Cyan"/> 
     </DataTemplate> 
    </Window.Resources> 

    <StackPanel x:Name="myStackPanel" DataContext="{StaticResource CompositeCollectionVM}"> 
     <StackPanel.Resources> 
      <CompositeCollection x:Key="compCollection"> 
       <CollectionContainer Collection="{Binding DataContext.GreekGods, Source={x:Reference myStackPanel}}" /> 
       <CollectionContainer Collection="{Binding Source={StaticResource GreekHeroesData}}" /> 
       <ListBoxItem Foreground="Magenta">Other Listbox Item 1</ListBoxItem> 
       <ListBoxItem Foreground="Magenta">Other Listbox Item 2</ListBoxItem> 
      </CompositeCollection> 
     </StackPanel.Resources> 
     <TextBlock FontSize="18" FontWeight="Bold" Margin="10" HorizontalAlignment="Center" Foreground="WhiteSmoke">Trying Composite Collections</TextBlock> 
     <DockPanel> 

      <ListBox Name="compositeListBox" ItemsSource="{Binding Source={StaticResource compCollection}}" Height="300" Background="#99333333" > 
      </ListBox> 
      <ListBox Name="greekGodsListBox" ItemsSource="{Binding GreekGods}" Background="#99333333" Margin="5,0" HorizontalAlignment="Right"> 
      </ListBox> 
     </DockPanel> 
    </StackPanel> 

</Window> 

Answer 1

El CompositeCollection no tiene DataContext, los enlaces en el CollectionContainers no funcionarán si se unen directamente a una propiedad (que utiliza implícitamente el DataContext como fuente).

Es necesario especificar explícitamente una fuente, yo sugeriría que un nombre al control con su DataContext y utilizar x:Reference conseguirlo (ElementName se no trabajo) o que utilice un StaticResource, por ejemplo,

<CollectionContainer Collection="{Binding DataContext.GreekGods, Source={x:Reference myStackPanel}}"/> 

<CollectionContainer Collection="{Binding GreekGods, Source={StaticResource CompositeCollectionVM}}"/> 

Tenga en cuenta que cuando se utiliza x:Reference el compilador fácilmente le hace tropezar con errores de dependencias cíclicas, para evitar los lugar su CompositeCollection en los recursos del control se hace referencia, a continuación, insertar dondequiera que pertenece utilizando la extensión de marcado StaticResource.

Answer 2

Un IMultiValueConverter es un buen complemento para CompositeCollection pero no para su caso específico donde agrega cosas en xaml.

Convertidor:

using System; 
using System.Collections; 
using System.Globalization; 
using System.Windows.Data; 

public class CompositeCollectionConverter : IMultiValueConverter 
{ 
    public static readonly CompositeCollectionConverter Default = new CompositeCollectionConverter(); 

    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture) 
    { 
     var compositeCollection = new CompositeCollection(); 
     foreach (var value in values) 
     { 
      var enumerable = value as IEnumerable; 
      if (enumerable != null) 
      { 
       compositeCollection.Add(new CollectionContainer { Collection = enumerable }); 
      } 
      else 
      { 
       compositeCollection.Add(value); 
      } 
     } 

     return compositeCollection; 
    } 

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture) 
    { 
     throw new NotSupportedException("CompositeCollectionConverter ony supports oneway bindings"); 
    } 
} 

Uso:

<ListBox> 
    <ListBox.ItemsSource> 
     <MultiBinding Converter="{x:Static local:CompositeCollectionConverter.Default}"> 
      <Binding Path="Col1" /> 
      <Binding Path="Col2" /> 
      ... 
     </MultiBinding> 
    </ListBox.ItemsSource> 
    ... 
</ListBox>