问WPF - CollectionView刷新在具有嵌套HierarchicalDataTemplate的TreeView中不丢失选择

EN

public interface INameable
{
    string Name { get; set; }
}

public class Quest : ViewModelBase, INameable
{
    private string _name;

    public string Name
    {
        get { return _name; }
        set
        {
            _name = value;

            RaisePropertyChanged();
        }
    }

    private ObservableCollection<Dialogue> _Dialogues;
    public ObservableCollection<Dialogue> Dialogues
    {
        get { return this._Dialogues; }
        set { this._Dialogues = value; RaisePropertyChanged(); }
    }

    private ICollectionView _SortedDialogues;
    public ICollectionView SortedDialogues
    {
        get { return this._SortedDialogues; }
        set { this._SortedDialogues = value; RaisePropertyChanged(); }
    }

    // this is actually a bit messy, I'll leave it to you to find a cleaner way of doing this
    public Func<object> GetSelected;
    public Action<object> SetSelected;

    public Quest()
    {
        Dialogues = new ObservableCollection<Dialogue>();

        this.SortedDialogues = CollectionViewSource.GetDefaultView(Dialogues);
        this.SortedDialogues.SortDescriptions.Add(new SortDescription("Name", ListSortDirection.Ascending));
    }

    public void AddDialogue(Dialogue dlg)
    {
        this.Dialogues.Add(dlg);
        dlg.PropertyChanged += Dlg_PropertyChanged;
        SortDialogues();
    }

    private void Dlg_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        SortDialogues();
    }

    private void SortDialogues()
    {
        var selected = GetSelected(); // get currently selected item
        this.SortedDialogues.Refresh(); // bam! treeviewitmes get destroyed.
        SetSelected(selected); // so reselect it immediately
    }
}

public class Dialogue : ViewModelBase, INameable
{
    private string _name;

    public string Name
    {
        get { return _name; }
        set
        {
            _name = value;
            RaisePropertyChanged();
        }
    }

}

public partial class MainWindow : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;


    private object _selectedObject = new object();
    public object SelectedObject
    {
        get
        {
            return _selectedObject;
        }
        set
        {
            _selectedObject = value;

            OnPropertyChanged();
        }
    }

    public ObservableCollection<Quest> Quests
    {
        get { return _quests; }
        set
        {
            _quests = value;
            OnPropertyChanged();
        }
    }

    private ObservableCollection<Quest> _quests;        

    public MainWindow()
    {
        Quests = new ObservableCollection<Quest>();

        InitializeComponent();
    }

    private void AddQuest(object sender, RoutedEventArgs e)
    {
        Quests.Add(new Quest
        {
            Name = "Quest",
            GetSelected = () => this.SelectedObject,
            SetSelected = (selected) => {
                ItemContainerGenerator gen = _treeView.ItemContainerGenerator;
                TreeViewItem item = ContainerFromItem(gen, selected);
                if (item != null)
                    item.IsSelected = true;
            }
            ,
        });
    }

    private void AddDialogue(object sender, RoutedEventArgs e)
    {
        if (_treeView.SelectedItem is Quest)
        {
            var dlg = new Dialogue
            {
                Name = "Dialogue"
            };
            (_treeView.SelectedItem as Quest).AddDialogue(dlg);
        }
    }

    // courtesy http://stackoverflow.com/questions/24859511/get-treeviewitem-for-treeview-logical-element
    private static TreeViewItem ContainerFromItem(ItemContainerGenerator containerGenerator, object item)
    {
        TreeViewItem container = (TreeViewItem)containerGenerator.ContainerFromItem(item);
        if (container != null)
            return container;

        foreach (object childItem in containerGenerator.Items)
        {
            TreeViewItem parent = containerGenerator.ContainerFromItem(childItem) as TreeViewItem;
            if (parent == null)
                continue;

            container = parent.ItemContainerGenerator.ContainerFromItem(item) as TreeViewItem;
            if (container != null)
                return container;

            container = ContainerFromItem(parent.ItemContainerGenerator, item);
            if (container != null)
                return container;
        }
        return null;
    }

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

}

    <TreeView x:Name="_treeView" behaviors:TreeViewHelper.SelectedItem="{Binding Path=SelectedObject, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">

        <TreeViewItem IsExpanded="True">

            <TreeViewItem.Header>
                <TextBlock Text="Project" Margin="5,0,0,0" />
            </TreeViewItem.Header>
            <TreeViewItem ItemsSource="{Binding Quests}" IsExpanded="True">
                <TreeViewItem.Header>
                    <TextBlock Text="Quests" Margin="5,0,0,0" />
                </TreeViewItem.Header>
                <TreeViewItem.Resources>
                    <HierarchicalDataTemplate DataType="{x:Type testApplication:Quest}" ItemsSource="{Binding SortedDialogues, UpdateSourceTrigger=PropertyChanged}">
                        <TextBlock Text="{Binding Name}" Margin="5,0,0,0" />
                    </HierarchicalDataTemplate>
                    <DataTemplate DataType="{x:Type testApplication:Dialogue}">
                        <TextBlock Text="{Binding Name}" Margin="5,0,0,0" />
                    </DataTemplate>
                </TreeViewItem.Resources>
            </TreeViewItem>
        </TreeViewItem>

    </TreeView>

public class TreeViewHelper
{
    private static Dictionary<DependencyObject, TreeViewSelectedItemBehavior> behaviors = new Dictionary<DependencyObject, TreeViewSelectedItemBehavior>();

    public static object GetSelectedItem(DependencyObject obj)
    {
        return (object)obj.GetValue(SelectedItemProperty);
    }

    public static void SetSelectedItem(DependencyObject obj, object value)
    {
        obj.SetValue(SelectedItemProperty, value);
    }

    // Using a DependencyProperty as the backing store for SelectedItem.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty SelectedItemProperty =
        DependencyProperty.RegisterAttached("SelectedItem", typeof(object), typeof(TreeViewHelper), new UIPropertyMetadata(null, SelectedItemChanged));

    private static void SelectedItemChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
    {
        if (!(obj is TreeView))
            return;

        if (!behaviors.ContainsKey(obj))
            behaviors.Add(obj, new TreeViewSelectedItemBehavior(obj as TreeView));

        TreeViewSelectedItemBehavior view = behaviors[obj];
        view.ChangeSelectedItem(e.NewValue);
    }

    private class TreeViewSelectedItemBehavior
    {
        TreeView view;
        public TreeViewSelectedItemBehavior(TreeView view)
        {
            this.view = view;
            view.SelectedItemChanged += (sender, e) => SetSelectedItem(view, e.NewValue);
        }

        internal void ChangeSelectedItem(object p)
        {
            TreeViewItem item = (TreeViewItem)view.ItemContainerGenerator.ContainerFromItem(p);
            // item will be null for HierarchicalDataTemplates
            if (item != null)
                item.IsSelected = true;
        }
    }
}