我有一个视图模型，其中包含一个公开事物集合的属性。 我有一个ComboBox，其ItemsSource属性绑定到此集合。 现在，用户可以从列表中进行选择。
我想允许用户清除选择，因此我想向ComboBox添加一个项目（即Null）。这很简单。
我决定尝试对ItemsSource使用CompositeCollection，这样我就可以将现有列表中的项目添加到ComboBox以及额外的Null项目。
在与此斗争一段时间后，我决定回到CompositeCollection Class上的文档。我复制了他们的示例并将其修改为使用视图模型而不是静态资源。
我发现当我将CollectionContainer绑定到ViewModel公开的列表时，列表中不会显示任何项目。
我不确定如何解决这个问题，我正在寻找有关此主题的任何建议。
这是我的XAML代码：
<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>
（正如你所看到的那样，当我将第二个ListBox的ItemsSource绑定到list属性时......项目显示出来）
这是我的VB.NET代码，它使XAML代码工作：
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
感谢您的帮助！
修改
H.B.的回答完美无缺。这是更新的工作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 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>
答案 0 :(得分：64)
CompositeCollection没有DataContext，CollectionContainers中的绑定如果直接绑定到属性（隐式使用DataContext作为源），则无效。
您需要明确指定来源，我建议您使用DataContext为控件命名并使用x:Reference来获取它（ElementName将不工作）或你使用StaticResource，例如
<CollectionContainer Collection="{Binding DataContext.GreekGods, Source={x:Reference myStackPanel}}"/>
<CollectionContainer Collection="{Binding GreekGods, Source={StaticResource CompositeCollectionVM}}"/>
请注意，使用x:Reference时，编译器会轻易将您与周期性依赖性错误联系起来，以避免将CompositeCollection放在您引用的控件的资源中，然后将其插入到所属的任何位置使用StaticResource标记扩展名。
答案 1 :(得分：3)
IMultiValueConverter非常适合CompositeCollection，但不适合您在xaml中添加内容的特定情况。
转换器：
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");
}
}
用法：
<ListBox>
<ListBox.ItemsSource>
<MultiBinding Converter="{x:Static local:CompositeCollectionConverter.Default}">
<Binding Path="Col1" />
<Binding Path="Col2" />
...
</MultiBinding>
</ListBox.ItemsSource>
...
</ListBox>