附加的属性仅附加在第一个用户控件实例上

按照Josh Smith关于mvvm工作区（客户视图）的示例，我有一个主窗口和一个主视图模型，其中包含"ChatTabViewModel"的ObservableCollection：

internal class FriendsListViewModel : ObservableObject
{
    #region bound properties
    private ICollectionView viewfriends;
    private ObservableCollection<ChatTabViewModel> _chatTab; 
    ...
    #endregion
}

我在xaml中有一个专门用于此集合的区域，如下所示：

<ContentControl Grid.Column="0" Grid.Row="0" Grid.RowSpan="2" Content="{Binding Path=ChatTabs}" ContentTemplate="{StaticResource ChatTabsTemplate}" />

在我的资源字典中：

<DataTemplate DataType="{x:Type vm:ChatTabViewModel}">
    <View:ChatTabView />
</DataTemplate>
<DataTemplate x:Key="ClosableTabItemTemplate">
    <DockPanel>
      <Button
        Command="{Binding Path=CloseCommand}"
        Content="X"
        Cursor="Hand"
        DockPanel.Dock="Right"
        Focusable="False"
        FontFamily="Courier"
        FontSize="9"
        FontWeight="Bold"
        Margin="0,1,0,0"
        Padding="0"
        VerticalContentAlignment="Bottom"
        Width="16" Height="16"
        />
      <ContentPresenter
        Content="{Binding Path=Caption, Mode=OneWay}"
        VerticalAlignment="Center">
      </ContentPresenter>
    </DockPanel>
</DataTemplate>
<DataTemplate x:Key="ChatTabsTemplate">
    <TabControl
      IsSynchronizedWithCurrentItem="True"
      ItemsSource="{Binding}"
      ItemTemplate="{StaticResource ClosableTabItemTemplate}"
      Margin="4"/>
</DataTemplate>

在用户事件中，我在集合中添加了一个新的ChattabViewModel，与它相关的视图显示在主窗口中。

但是，当我尝试在ChattabView的滚动条上添加附加的属性时，该属性将仅附加在第一个ChattabViewModel实例上，其他选项卡将不会绑定到附加的属性。这是ChattabView XAML：

 <ScrollViewer VerticalScrollBarVisibility="Auto" Grid.Row="0">
  <ItemsControl ItemsSource="{Binding Messages}" View:ItemsControlBehavior.ScrollOnNewItem="True">
  <ItemsControl.ItemTemplate>
    <DataTemplate>
        <TextBox IsReadOnly="True" TextWrapping="Wrap" Text="{Binding Path=DataContext, RelativeSource={RelativeSource Self}}" />
    </DataTemplate>
  </ItemsControl.ItemTemplate>    
</ItemsControl>
</ScrollViewer>

以及所附财产的代码：

namespace GtalkOntre.View
{
    /// <summary>
    /// Util class to scroll down when a new message is added.
    /// </summary>
    /// <remarks>attached property called ScrollOnNewItem that when set to true hooks into the INotifyCollectionChanged events of the itemscontrol items source and upon detecting a new item, scrolls the scrollbar to it.</remarks>
    public class ItemsControlBehavior
    {
        static Dictionary<ItemsControl, Capture> Associations = new Dictionary<ItemsControl, Capture>();
        public static bool GetScrollOnNewItem(DependencyObject obj)
        {
            return (bool)obj.GetValue(ScrollOnNewItemProperty);
        }
        public static void SetScrollOnNewItem(DependencyObject obj, bool value)
        {
            obj.SetValue(ScrollOnNewItemProperty, value);
        }          
        public static DependencyProperty ScrollOnNewItemProperty =
            DependencyProperty .RegisterAttached(
                "ScrollOnNewItem",
                typeof(bool),
                typeof(ItemsControlBehavior),
                new UIPropertyMetadata(false, OnScrollOnNewItemChanged));
        public static void OnScrollOnNewItemChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var mycontrol = d as ItemsControl;
            if (mycontrol == null) return;
            bool newValue = (bool)e.NewValue;
            if (newValue)
            {
                mycontrol.Loaded += MyControl_Loaded;
                mycontrol.Unloaded += MyControl_Unloaded;
            }
            else
            {
                mycontrol.Loaded -= MyControl_Loaded;
                mycontrol.Unloaded -= MyControl_Unloaded;
                if (Associations.ContainsKey(mycontrol))
                    Associations[mycontrol].Dispose();
            }
        }
        static void MyControl_Unloaded(object sender, RoutedEventArgs e)
        {
            var mycontrol = (ItemsControl)sender;
            Associations[mycontrol].Dispose();
            mycontrol.Unloaded -= MyControl_Unloaded;
        }
        static void MyControl_Loaded(object sender, RoutedEventArgs e)
        {
            var mycontrol = (ItemsControl)sender;
            var incc = mycontrol.Items as INotifyCollectionChanged;
            if (incc == null) return;
            mycontrol.Loaded -= MyControl_Loaded;
            Associations[mycontrol] = new Capture(mycontrol);
        }
        class Capture : IDisposable
        {
            public ItemsControl mycontrol { get; set; }
            public INotifyCollectionChanged incc { get; set; }
            public Capture(ItemsControl mycontrol)
            {
                this.mycontrol = mycontrol;
                incc = mycontrol.ItemsSource as INotifyCollectionChanged;
                incc.CollectionChanged +=incc_CollectionChanged;
            }
            void incc_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
            {                
                if (e.Action == NotifyCollectionChangedAction.Add)
                {
                    ScrollViewer sv = mycontrol.Parent as ScrollViewer;
                    sv.ScrollToBottom();
                }
            }
            public void Dispose()
            {
                incc.CollectionChanged -= incc_CollectionChanged;
            }
        }
    }
}

那么，为什么在chattableviewmodel集合的第一次"chattableview"出现时，附加的属性只绑定一次呢？因此，只在第一个聊天表视图模型上工作。当我关闭它们时，附加的属性将在chattableviewmodel的最后一个实例上解除绑定，当我添加新的第一个chattableview模型时，该属性将正确绑定。因此，它只在mainwindowviewmodel的"chattableviewmodel"集合的第一个实例和最后一个实例上触发。

经过一周的寻找，我现在有点绝望了。。。

到目前为止，我的假设是：这个问题可能与我在字典资源中为视图模型设置视图的方式有关。视图可能是共享的，并且第一个滚动条可能只会做出反应。我试图在DataTemplate标记上添加一个x:Shared = false属性，但它没有改变任何内容。