从子xaml检索treeviewitem的datacontext

我有一个DataBound树视图，可从中创建/显示treeviewitems并具有上下文菜单。这工作正常。然后，我尝试使用自定义menuitem类，以便可以通过从contextmenu菜单中触发的命令来检索treeviewitem的datacontext。抱歉，这令人困惑。我这样做可能走错了路。

这是我的xaml。

<UserControl x:Class="Pipeline_General.Custom_Controls.ProjectTree"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:pm="clr-namespace:Pipeline_General"
         mc:Ignorable="d" 
         DataContext = "{Binding RelativeSource={RelativeSource Self}}"
         d:DesignHeight="300" d:DesignWidth="300">
<Grid>
    <TreeView Name="StructureTree" Background="{x:Static pm:myBrushes.defaultBG}" ItemsSource="{Binding ProjectList}">
        <TreeView.ItemContainerStyle>
            <Style TargetType="{x:Type TreeViewItem}">
                <Setter Property="IsExpanded" Value="True"/>
                <Setter Property="Margin" Value="5,5,5,5" />
                <Setter Property="ContextMenu">
                    <Setter.Value>
                        <ContextMenu Background="{x:Static pm:myBrushes.defaultBG}" Foreground="{x:Static pm:myBrushes.gray}">
                            <pm:ProjectTreeMenuItem Header="Add Episode.." 
                                    Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                      Command="{x:Static pm:MyCommands.AddEpCommand}" 
                                      CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                      Margin="20,0"/>
                            <pm:ProjectTreeMenuItem Header="Add Sequence.." 
                                      Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                      Command="{x:Static pm:MyCommands.AddSeqCommand}" 
                                      CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                      Margin="20,0"/>
                            <pm:ProjectTreeMenuItem Header="Add Scene.." 
                                        Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                      Command="{x:Static pm:MyCommands.AddScCommand}" 
                                      CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                      Margin="20,0"/>
                        </ContextMenu>
                    </Setter.Value>
                </Setter>
            </Style>
        </TreeView.ItemContainerStyle>
        <TreeView.ItemTemplate>
            <HierarchicalDataTemplate DataType="{x:Type pm:ProjectRoot}" ItemsSource="{Binding Episodes}">
                <TextBlock Text="{Binding Path=Title}" Foreground="{x:Static pm:myBrushes.pink}"
                           FontFamily="Calibri" FontSize="18"/>
                <HierarchicalDataTemplate.ItemContainerStyle>
                    <Style TargetType="{x:Type TreeViewItem}">
                        <Setter Property="IsExpanded" Value="True"/>
                        <Setter Property="Margin" Value="5,5,5,5" />
                        <Setter Property="ContextMenu">
                            <Setter.Value>
                                <ContextMenu Background="{x:Static pm:myBrushes.defaultBG}" Foreground="{x:Static pm:myBrushes.gray}">
                                    <pm:ProjectTreeMenuItem Header="Add Sequence.."  
                                     Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                     Command="{x:Static pm:MyCommands.AddSeqCommand}" 
                                      CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                      Margin="20,0"/>
                                    <pm:ProjectTreeMenuItem Header="Add Scene.."
                                      Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                      Command="{x:Static pm:MyCommands.AddScCommand}" 
                                      CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                      Margin="20,0"/>
                                    <Separator Height="15" Margin="20,0"/>
                                    <pm:ProjectTreeMenuItem Header="Cut" 
                                    Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                    Command="{x:Static pm:MyCommands.CutCommand}" 
                                      CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                      Margin="20,0"/>
                                    <pm:ProjectTreeMenuItem Header="Un-Cut" 
                                    Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                    Command="{x:Static pm:MyCommands.UnCutCommand}" 
                                      CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                      Margin="20,0"/>
                                </ContextMenu>
                            </Setter.Value>
                        </Setter>
                    </Style>
                </HierarchicalDataTemplate.ItemContainerStyle>


                <HierarchicalDataTemplate.ItemTemplate>
                    <HierarchicalDataTemplate DataType="{x:Type pm:Episode}" ItemsSource="{Binding Sequences}">
                        <TextBlock Text="{Binding Path=Key}" Foreground="{x:Static pm:myBrushes.yellow}"
                                           FontFamily="Calibri" FontSize="14"/>
                        <HierarchicalDataTemplate.ItemContainerStyle>
                            <Style TargetType="{x:Type TreeViewItem}">
                                <Setter Property="IsExpanded" Value="True"/>
                                <Setter Property="Margin" Value="5,5,5,5" />
                                <Setter Property="ContextMenu">
                                    <Setter.Value>
                                        <ContextMenu Background="{x:Static pm:myBrushes.defaultBG}" Foreground="{x:Static pm:myBrushes.gray}">
                                            <pm:ProjectTreeMenuItem Header="Add Scene.." 
                                             Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                             Command="{x:Static pm:MyCommands.AddScCommand}" 
                                            CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                            Margin="20,0"/>
                                            <Separator Height="15" Margin="20,0"/>
                                            <pm:ProjectTreeMenuItem Header="Cut" 
                                            Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                            Command="{x:Static pm:MyCommands.CutCommand}" 
                                            CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                            Margin="20,0"/>
                                            <pm:ProjectTreeMenuItem Header="Un-Cut" 
                                             Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                            Command="{x:Static pm:MyCommands.UnCutCommand}" 
                                            CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                             Margin="20,0"/>
                                        </ContextMenu>
                                    </Setter.Value>
                                </Setter>
                            </Style>
                        </HierarchicalDataTemplate.ItemContainerStyle>

                        <HierarchicalDataTemplate.ItemTemplate>
                            <HierarchicalDataTemplate DataType="{x:Type pm:Sequence}" ItemsSource="{Binding Scenes}">
                                <TextBlock Text="{Binding Path=Key}" Foreground="{x:Static pm:myBrushes.yellow}"
                                           FontFamily="Calibri" FontSize="14"/>
                                <HierarchicalDataTemplate.ItemContainerStyle>
                                    <Style TargetType="{x:Type TreeViewItem}">
                                        <Setter Property="ContextMenu">
                                            <Setter.Value>
                                                <ContextMenu Background="{x:Static pm:myBrushes.defaultBG}" Foreground="{x:Static pm:myBrushes.gray}">
                                                    <pm:ProjectTreeMenuItem Header="Cut" 
                                                        Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                                        Command="{x:Static pm:MyCommands.CutCommand}" 
                                                        CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                                        Margin="20,0"/>
                                                    <pm:ProjectTreeMenuItem Header="Un-Cut" 
                                                         Element="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}"
                                                        Command="{x:Static pm:MyCommands.UnCutCommand}" 
                                                        CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
                                                         Margin="20,0"/>
                                                </ContextMenu>
                                            </Setter.Value>
                                        </Setter>
                                    </Style>
                                </HierarchicalDataTemplate.ItemContainerStyle>
                            </HierarchicalDataTemplate>
                        </HierarchicalDataTemplate.ItemTemplate>
                    </HierarchicalDataTemplate>
                </HierarchicalDataTemplate.ItemTemplate>
            </HierarchicalDataTemplate>
        </TreeView.ItemTemplate>
    </TreeView>
</Grid>

以及我的自定义菜单项类和命令。

public static class MyCommands
{
    static MyCommands()
    {
        AddEpCommand = new SimpleDelegateCommand(p =>
        {
            var menuItem = p as ProjectTreeMenuItem;
            var Element = menuItem.Element as ProjectElement;
            Console.WriteLine(Element.Key);
            Console.WriteLine("EP");
        });

        AddSeqCommand = new SimpleDelegateCommand(p =>
        {
            var menuItem = p as ProjectTreeMenuItem;
            var Element = menuItem.Element as ProjectElement;
            Console.WriteLine(Element.Key);
            Console.WriteLine("SEQ");
        });

        AddScCommand = new SimpleDelegateCommand(p =>
        {
            var menuItem = p as ProjectTreeMenuItem;
            var Element = menuItem.Element as ProjectElement;
            Console.WriteLine(Element.Key);
            Console.WriteLine("SC");
        });

        CutCommand = new SimpleDelegateCommand(p =>
        {
            var menuItem = p as ProjectTreeMenuItem;
            var Element = menuItem.Element as ProjectElement;
            Console.WriteLine(Element.Key);
            Console.WriteLine("SC");
        });

        UnCutCommand = new SimpleDelegateCommand(p =>
        {
            var menuItem = p as ProjectTreeMenuItem;
            var Element = menuItem.Element as ProjectElement;
            Console.WriteLine(Element.Key);
            Console.WriteLine("SC");
        });
    }

    public static ICommand AddEpCommand { get; set; }
    public static ICommand AddSeqCommand { get; set; }
    public static ICommand AddScCommand { get; set; }
    public static ICommand CutCommand { get; set; }
    public static ICommand UnCutCommand { get; set; }
}

public class SimpleDelegateCommand : ICommand
{
    public SimpleDelegateCommand(Action<object> executeAction)
    {
        _executeAction = executeAction;
    }

    private Action<object> _executeAction;

    public bool CanExecute(object parameter)
    {
        return true;
    }

    public event EventHandler CanExecuteChanged;

    public void Execute(object parameter)
    {
        _executeAction(parameter);
    }
}

public class ProjectTreeMenuItem : MenuItem
{
    #region Element (DependencyProperty)
    public ProjectElement Element
    {
        get { return (ProjectElement)GetValue(ElementProperty); }
        set { SetValue(ElementProperty, value); }
    }
    public static readonly DependencyProperty ElementProperty =
        DependencyProperty.Register("Element", typeof(ProjectElement), typeof(ProjectTreeMenuItem),
          new PropertyMetadata { PropertyChangedCallback = ElementChanged });
    private static void ElementChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        ProjectTreeMenuItem so = d as ProjectTreeMenuItem;
        if (so != null && e.NewValue != null)
        {
            so.Element = (ProjectElement)e.NewValue;
            Console.WriteLine("HERE " + so.Element.Title);
        }
    }
    #endregion

    public ProjectTreeMenuItem()
        :base()
    {

    }
}

projectElement类（在项目中的其他数百个地方都使用过）具有String Key，String Title属性，该属性在其他地方也可以正常使用。我很确定我的问题在于通过datacontext通过xaml设置Element属性。