WPF用户控制MVVM

在网站上搜索了很多并阅读了很多类似的问题，但似乎没有解决我用户控件无法理解的问题 .

我有一个用MVVM实现的用户控件 . 基本上是一个文件夹网格，其中每个文件夹都是一个复选框和一个路径 . 用户可以选中任何检查复选框的文件夹 . User Control xaml 是：

<UserControl x:Class="TestDP.Views.ViewCTRL" [...]>
        <DataGrid Name="GridMain" ItemsSource="{Binding Folders}">
        <DataGrid.Columns>
            <DataGridCheckBoxColumn Header="Cked" Binding="{Binding Cked,  UpdateSourceTrigger=PropertyChanged}" />
            <DataGridTextColumn Header="Path" Binding="{Binding Path}"/>
        </DataGrid.Columns>
    </DataGrid>
</UserControl>

User control code behind 是：

public partial class ViewCTRL : UserControld
{
    public static DependencyProperty SelectedFoldersProperty =
        DependencyProperty.Register("SelectedFolders", typeof(ObservableCollection<Folder>), typeof(ViewCTRL),
        new FrameworkPropertyMetadata() { BindsTwoWayByDefault = true });

    public ObservableCollection<Folder> SelectedFolders
    {
        get{return (ObservableCollection<Folder>)GetValue(SelectedFoldersProperty);}
        set{SetValue(SelectedFoldersProperty, value);}}

    public ViewCTRL()
    {
        var vm = new ViewCTRLModel();
        InitializeComponent();
        GridMain.DataContext = vm;

        // bindings
        SetBinding(SelectedFoldersProperty, new Binding()
        {
            Source = GridMain.DataContext,
            Path = new PropertyPath("SelectedFoldersV"),
            UpdateSourceTrigger =   System.Windows.Data.UpdateSourceTrigger.PropertyChanged,
            Mode = BindingMode.TwoWay
        });
    }

User Control ViewModel 是：

public class ViewCTRLModel : INotifyPropertyChanged
{
    [...]

    public void Folder_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        SelectedFoldersV = new ObservableCollection<Folder>(Folders.Where(x => x.Cked));
    }

    private ObservableCollection<Folder> folders;
    public ObservableCollection<Folder> Folders
    {
        get{return folders;}
        set{folders = value;OnPropertyChanged("Folders");}
    }

    private ObservableCollection<Folder> selectedFoldersV;
    public ObservableCollection<Folder> SelectedFoldersV
    {
        get{return selectedFoldersV;}
        set{selectedFoldersV = value;OnPropertyChanged("SelectedFoldersV");}
    }
    [...]
}

然后我使用WPF应用程序，我放置了我的用户控件 . 如果我将用户控件DP SelectedFolders绑定到 ItemSource ，则一切正常 . 如果我检查用户控件的文件夹复选框，则选择项目源上的SelectedFolder .

<Window x:Class="TestDPWPF.Views.ViewWPF" [...]>
<uc:ViewCTRL Name="ViewCTRL" />
<ListBox ItemsSource="{Binding ElementName=ViewCTRL, Path=SelectedFolders}" DisplayMemberPath="Path"/>

If I Bind the SelectedFolders Propery to a Property of the Window view model like ：

<uc:ViewCTRL Name="ViewCTRL" SelectedFolders="{Binding SelectedFoldersVMWPF,  Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />

the usercontrol get the initial values passed by the window viewmodel but then binding seems broken and selecting any folder does not update the SelectedFoldersVMWPF binding.

Viewmodel of the windows 是：

class ViewWPFModel : INotifyPropertyChanged
{
    public ViewWPFModel()
    {
        SelectedFoldersVMWPF = new ObservableCollection<Folder>();
        SelectedFoldersVMWPF.Add(new Folder() { Path = "uuu" });
    }

    private ObservableCollection<Folder> selectedFoldersVMWPF;
    public ObservableCollection<Folder> SelectedFoldersVMWPF
    {
        get {return selectedFoldersVMWPF;}
        set {selectedFoldersVMWPF = value; OnPropertyChanged("SelectedFoldersVMWPF");}
    }
}

我在输出窗口中没有关于绑定的任何消息，因此所有绑定路径都应该没问题 . 我认为窗口视图模型和控件的DP之间的绑定是由用户控件和用户控件视图模型之间的绑定决定的 . 但我不知道为什么以及如何解决这个问题 . 我尝试以多种方式更改用户控件的DataContex，但结果始终相同 . 任何人都可以带领我朝着正确的方向前进