Datagrid with ICollectionView SortDescription got lost - Bug?

Question

here is what i want: if i bind a ICollectionview to a DataGrid, i dont wanna loose the SortDescription in my Viewmodel.

i create a small sample project to see what i mean. In my projects i simply use a Usercontrol to show my data in a DataGrid. If i do this the SortDescritpion is gone when the UserControl Unload, because the ItemsSource is set to null. If i use a TemplateSelector to show my UserControl, the SortDescription is not gone and the ItemsSource ist not set to null on Unload. the question is, why are these different behaviors? Is one on the 2 behaviors a bug?

btw. I use .Net 4.5.1 but 4.6.1 is installed and system.Windows.Interactivity 4.0.0.0

MainWindow.xaml

MainWindow.xaml.cs

namespace DataGridICollectionView
{
/// 
/// Interaktionslogik für MainWindow.xaml
/// 
public partial class MainWindow : Window, INotifyPropertyChanged
{
    private object _workspace;

    public MainWindow()
    {
        InitializeComponent();
        MyViewVm = new ViewmodelListe();

        DataContext = this;
    }

    public ViewmodelListe MyViewVm { get; set; }

    public object Workspace
    {
        get { return _workspace; }
        set
        {
            _workspace = value;
            OnPropertyChanged();
        }
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        Workspace = MyViewVm;
    }

    private void Button_Click_1(object sender, RoutedEventArgs e)
    {
        Workspace = "Other";
    }

    public event PropertyChangedEventHandler PropertyChanged;

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

public class ViewmodelListe : INotifyPropertyChanged
{
    public ViewmodelListe()
    {
        Persons = new ObservableCollection();
        MyView = CollectionViewSource.GetDefaultView(Persons);

        Persons.Add(new Person() {FirstName = "P1", LastName = "L1"});
        Persons.Add(new Person() {FirstName = "P2", LastName = "L2"});
        Persons.Add(new Person() {FirstName = "P3", LastName = "L3"});
    }

    public ObservableCollection Persons { get; private set; }

    public ICollectionView MyView { get; private set; } 

    public event PropertyChangedEventHandler PropertyChanged;

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

public class Person : INotifyPropertyChanged
{
    private string _firstName;
    private string _lastName;

    public string FirstName
    {
        get { return _firstName; }
        set
        {
            _firstName = value; 
            OnPropertyChanged();
        }
    }

    public string LastName
    {
        get { return _lastName; }
        set
        {
            _lastName = value;
            OnPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

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

public class TestBehavior : Behavior
{
    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.Unloaded += AssociatedObjectUnloaded;
    }

    private void AssociatedObjectUnloaded(object sender, RoutedEventArgs e)
    {
        //look at this in Debug Mode, its NULL if you dont use the TemplateSelector
        var itemssource = AssociatedObject.ItemsSource;


    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.Unloaded -= AssociatedObjectUnloaded;
    }
}
}

MyGridControl.xaml

MyViewUc.xaml

MyViewUc.xaml.cs

namespace DataGridICollectionView
{
/// 
/// Interaktionslogik für MyViewUc.xaml
/// 
public partial class MyViewUc : UserControl
{
    public MyViewUc()
    {
        InitializeComponent();
    }
}

public class MyTemplateSelector : DataTemplateSelector
{
    public DataTemplate GridView { get; set; }


    public override DataTemplate SelectTemplate(object item, System.Windows.DependencyObject container)
    {
        var chooser = item as ViewmodelListe;
        if (chooser == null)
        {
            return base.SelectTemplate(item, container);
        }

        return GridView;
    }
}
}

EDIT: i end up using this

public class MyDataGrid : DataGrid
{

    static MyDataGrid ()
    {
        ItemsSourceProperty.OverrideMetadata(typeof(MyDataGrid ),new FrameworkPropertyMetadata(null, OnPropertyChangedCallBack, OnCoerceItemsSourceProperty));
    }

    private ICollectionView _defaultView;
    protected override void OnItemsSourceChanged(IEnumerable oldValue, IEnumerable newValue)
    {
        if(_defaultView != null)
            _defaultView.CollectionChanged -= LiveSortingPropertiesOnCollectionChanged;

        base.OnItemsSourceChanged(oldValue, newValue);

        _defaultView = newValue as ICollectionView;
        if(_defaultView != null)
            _defaultView.CollectionChanged += LiveSortingPropertiesOnCollectionChanged;
    }

    private void LiveSortingPropertiesOnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Reset)
        {
            foreach (var dataGridColumn in this.Columns)
            {
                var isSortDirectionSetFromCollectionView = false;
                foreach (var sortDescription in _defaultView.SortDescriptions)
                {
                    if (dataGridColumn.SortMemberPath == sortDescription.PropertyName)
                    {
                        dataGridColumn.SortDirection = sortDescription.Direction;
                        isSortDirectionSetFromCollectionView = true;
                        break;
                    }
                }

                if (!isSortDirectionSetFromCollectionView)
                {
                    dataGridColumn.SortDirection = null;
                }
            }
        }
    }

    private static void OnPropertyChangedCallBack(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var grd = d as MyDataGrid ;
        var view = e.NewValue as ICollectionView;

        if (grd == null || view == null)
            return;

        foreach (var dataGridColumn in grd.Columns)
        {
            var isSortDirectionSetFromCollectionView = false;
            foreach (var sortDescription in view.SortDescriptions)
            {
                if (dataGridColumn.SortMemberPath == sortDescription.PropertyName)
                {
                    dataGridColumn.SortDirection = sortDescription.Direction;
                    isSortDirectionSetFromCollectionView = true;
                    break;
                }
            }
            //wenn die View nicht sortiert war, auch die column nicht Sortieren
            if (!isSortDirectionSetFromCollectionView)
            {
                dataGridColumn.SortDirection = null;
            }
        }
    }


    private static object OnCoerceItemsSourceProperty(DependencyObject d, object baseValue)
    {
        // do nothing here - we just want to override parent behaviour.
        // The _only_ thing DataGrid does here is clearing sort descriptors
        return baseValue;
    }


}

Datagrid with ICollectionView SortDescription got lost - Bug?

1 Answers