WPF:列表框项上下文菜单/菜单项上的命令不起作用，即使它在按钮上也不起作用

参考我的代码。它对我来说工作正常。

<UserControl x:Class="DragDrop_Learning.UserControl1"
         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" 
         mc:Ignorable="d" 
         xmlns:local="clr-namespace:DragDrop_Learning"
         d:DesignHeight="300" d:DesignWidth="300">
<UserControl.CommandBindings>
    <CommandBinding Command="local:CrawlCommands.AddCredit" Executed="ExecutedAddCredit" CanExecute="CanExecuteAddCredit"/>
    <CommandBinding Command="local:CrawlCommands.AddCreditBlock" Executed="ExecutedAddCreditBlock" CanExecute="CanExecuteAddCreditBlock"/>
</UserControl.CommandBindings>
<Grid>
    <Grid.Resources>
    </Grid.Resources>
    <Grid.Background>
        <SolidColorBrush Color="DarkGray"/>
    </Grid.Background>
    <Grid.RowDefinitions>
        <RowDefinition Height="7*"/>
        <RowDefinition Height="3*"/>
    </Grid.RowDefinitions>
    <!-- A button with a command, this one works! -->
    <Button x:Name="button" Command="local:CrawlCommands.AddCredit" Content="Add Credit" Margin="10" Grid.Row="1" Width="177"/>
    <ListBox x:Name="listBox" Margin="10" Background="LightBlue" >
        <ListBox.Resources>
            <!-- Define a context menu -->
            <ContextMenu x:Key="ItemMenu">
                <MenuItem Command="local:CrawlCommands.AddCreditBlock"/>
            </ContextMenu>
            <!-- Sets a context menu for each ListBoxItem in the current ListBox -->
            <Style TargetType="{x:Type ListBoxItem}">
                <!-- This menu item will not function even though the button verison above does -->
                <Setter Property="ContextMenu" Value="{StaticResource ItemMenu}"></Setter>
            </Style>
        </ListBox.Resources>
        <ListBox.ItemTemplate>
            <DataTemplate>
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="{Binding FirstName}"/>
                </StackPanel>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>
</Grid>

 public partial class UserControl1 : UserControl
{
    public UserControl1()
    {
        InitializeComponent();
        List<Person> lst = new List<Person>();
        listBox.ItemsSource = lst;
        lst.Add(new Person() { FirstName="Test"});
    }
    private void CanExecuteAddCredit(object sender, CanExecuteRoutedEventArgs e)
    {
        e.CanExecute = true;
    }
    private void ExecutedAddCredit(object sender, ExecutedRoutedEventArgs e)
    {
    }
    private void CanExecuteAddCreditBlock(object sender, CanExecuteRoutedEventArgs e)
    {
        e.CanExecute = true;
    }
    private void ExecutedAddCreditBlock(object sender, ExecutedRoutedEventArgs e)
    {
    }
}
public static class CrawlCommands
{
    public static readonly RoutedUICommand AddCredit = new RoutedUICommand
            (
                    "AddCredit",
                    "AddCredit",
                    typeof(CrawlCommands)
            );
    public static readonly RoutedUICommand AddCreditBlock = new RoutedUICommand
            (
                    "AddCreditBlock",
                    "AddCreditBlock",
                    typeof(CrawlCommands)
            );
}
class Person
{
    private string myVar;
    public string FirstName
    {
        get { return myVar; }
        set { myVar = value; }
    }
}