PropertyGrid in ItemsControl ItemTemplate is always empty

No repository files or tests are named. Start by reproducing the supplied WPF ListBox and PropertyGrid XAML with the Company and ViewModel example, then trace the PropertyDefinitions binding inside the DataTemplate. Done means each PropertyGrid receives the collection and displays the Task and HeadNote properties.

I bind PropertyGrid(in ListBox ItemTemplate) PropertyDefinitions to a PropertyDefinitionCollection in my viewmodel, but I find the binding does not work, the PropertyDefinitionCollection of all PropertyGrid is empty, and all PropertyGrid are empty. Here is my code:

<ListBox ItemsSource="{Binding  ManufacturerList}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <xctk:PropertyGrid
                SelectedObject="{Binding }"
                AutoGenerateProperties="False"
                PropertyDefinitions="{Binding DataContext.PropertyDefinitionCollection, ElementName=window}">
            </xctk:PropertyGrid>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

public class Company
{
    public string Task { get; set; }
    public string HeadNote { get; set; }
}

public class ViewModel
{
    public PropertyDefinitionCollection PropertyDefinitionCollection { get; set; } =
        new PropertyDefinitionCollection()
        {
            new PropertyDefinition()
            {
                TargetProperties = new[] { "Task" }
            },
            new PropertyDefinition()
            {
                TargetProperties = new[] { "HeadNote" }
            }
        };

    public List<Company> ManufacturerList { get; set; }

    public ViewModel()
    {
        List<Company> list = new List<Company>();

        list.Add(new Company()
        {
            Task = "Coding",
            HeadNote = "Coding Task",
                
        });


        list.Add(new Company()
        {
            Task = "Communicate",
            HeadNote = "Communicate Task",
        });

        ManufacturerList = list;
    }
}