CollectionView only sorting first time (when create viewmodel again it doesnt)

Question

I have problems to understand the CollectionView. I implemented it with some sorting/grouping. But it is only sorting the first time the view is created.

View:

<DataGrid ItemsSource="{Binding varCollectionview}" Grid.Row="2" AutoGenerateColumns="False" SelectedItem="{Binding selVariable}" Grid.ColumnSpan="2">
        <DataGrid.GroupStyle>
            <GroupStyle>
                <GroupStyle.ContainerStyle>
                    <Style TargetType="{x:Type GroupItem}">
                        <Setter Property="Template">
                            <Setter.Value>
                                <ControlTemplate>
                                    <StackPanel Orientation="Vertical">
                                        <TextBlock Text="{Binding Name.value}" Foreground="White" Background="Gray" HorizontalAlignment="Stretch" TextAlignment="Left" Padding="10,0" />
                                        <ItemsPresenter></ItemsPresenter>
                                    </StackPanel>

                                </ControlTemplate>
                            </Setter.Value>
                        </Setter>

                    </Style>
                </GroupStyle.ContainerStyle></GroupStyle>
        </DataGrid.GroupStyle>
        <i:Interaction.Behaviors>
            <behavior:DataGridScrollIntoViewBehavior />
        </i:Interaction.Behaviors>
        <DataGrid.Columns>
        ...
        ...

the MainViewModel call:

variablenVm = new VariablenViewModel(cfg);

it is called everytime i load other values etc. for reloading the Tab.

the actual ViewModel for the TabItem:

public class VariablenViewModel : ViewModelBase
{
    private string _filterString;
    public string filterString 
    {
        get { return _filterString ; }
        set
        {
            _filterString = value.ToLower();
            RaisePropertyChanged("filterString ");
            varCollectionview.Refresh();
        }
    }
    private SimuVariable _selVariable;
    public SimuVariable selVariable
    {
        get { return _selVariable; }
        set
        {
            _selVariable = value;
            RaisePropertyChanged("selVariable");
        }
    }
    private Konfiguration _cfg;
    public Konfiguration cfg
    {
        get { return _cfg; }
        set
        {
            _cfg = value;
            RaisePropertyChanged("cfg");
        }
    }
    private ICollectionView _varCollectionview;
    public ICollectionView varCollectionview
    {
        get { return _varCollectionview; }
        set
        {
            _varCollectionview = value;
            RaisePropertyChanged("varCollectionview");
        }
    }

    public VariablenViewModel(Konfiguration _mainCfg)
    {
        cfg = _mainCfg;
        hasSomeValueChanged = false;
        _filterString = "";

        _neueVariableCommand = new RelayCommand(() =>
        {
...
        });
        _loescheVariableCommand = new RelayCommand(
...
        );
        varCollectionview = (CollectionView)CollectionViewSource.GetDefaultView(cfg.variablen);
        if (varCollectionview.GroupDescriptions.Count == 0)
        {
            varCollectionview.GroupDescriptions.Add(new PropertyGroupDescription("varType"));
        }
        if (varCollectionview.SortDescriptions.Count == 0)
        {
            varCollectionview.SortDescriptions.Add(new SortDescription("varType", ListSortDirection.Descending));
            varCollectionview.SortDescriptions.Add(new SortDescription("name", ListSortDirection.Ascending));
        }
        varCollectionview.Filter = new Predicate<object>(filter);
        varCollectionview.Refresh();
    }

    ...
    }

edit: When i first look at the view, the collection is sorted. If i create a new Viewmodel after that, sorting doesnt happen.

After some Debugging i found out that the Sortdescriptions get lost. In the Constructor i add 2 Sortdescription and 1 groupdescription. Some time later i have only the groupdescription left and the sorts are gone and i don't know why :(

https://i.stack.imgur.com/4HYp0.jpg -somewhere the SortDescriptions are lost/deleted

Another question, is it possible to add a SortDescription like varType.id?

@Default: not clear doesnt change the behavior, just tested ->if (varCollectionview.SortDescriptions.Count == 0) -> add — Michael Spannbauer, Jan 09 '15 at 10:14
@Aron: hmm this behavior seems to be gone. But someday, after calling GetDefaultView i had the sortdescriptions from the last viewmodel instance. But this doesn't change the fact that the sortdescription only has effect on first time creating this ViewModel. — Michael Spannbauer, Jan 09 '15 at 10:19
refresh doesn't help. I noticed that the sorting is correct the first time i "look" at the View, even if the viewmodel changed a few times. After the view is created, when i change the viewmodel it doesn't sort — Michael Spannbauer, Jan 09 '15 at 10:30
Could you provide some more code? Complete constructor code might be helpful. Maybe even the whole class - at least the members that are related to the CollectionView. — gehho, Jan 09 '15 at 10:48
Mmmh, the code seems to be correct. However, CollectionViews are sometimes strange. What happens if you replace `CollectionViewSource.GetDefaultView` with `new ListCollectionView`? Instead of getting the default view (which will always be the same if `cfg.variablen` is the same instance), this creates a new CollectionView every time. — gehho, Jan 09 '15 at 11:16
Another idea is to get rid of those `SortDescriptions` (which are pretty slow if you have lots of items due to reflection) and instead implement `IComparable` in your items, and then set `ListCollectionView.CustomSort = Comparer.Default`. Of course you could also implement your own custom `IComparer` if you prefer that. — gehho, Jan 09 '15 at 11:19
@gehho: varCollectionview = new ListCollectionView(cfg.variablen) has the same behavior :( .. Thanks for the tip with IComparable, i will notice it when creating a new project, but here i have ~50 items so i think its not worth. — Michael Spannbauer, Jan 09 '15 at 11:31
After some Debugging i found out that the Sortdescriptions get lost. In the Construktor i add 2 Sortdescription and 1 groupdescription Some time later i have only the groupdescription left and the sorts are gone :( — Michael Spannbauer, Jan 12 '15 at 09:28

score 0 · Accepted Answer · answered Jan 12 '15 at 09:58

Hell yeah, i found a Solution.

varCollectionview = new CollectionViewSource();
        varCollectionview.Source = cfg.variablen;
        Dispatcher.CurrentDispatcher.BeginInvoke(DispatcherPriority.Background, new Action(delegate()
            {
        varCollectionview.View.SortDescriptions.Add(new SortDescription("varType", ListSortDirection.Descending));
        varCollectionview.View.SortDescriptions.Add(new SortDescription("name", ListSortDirection.Ascending));
        varCollectionview.View.GroupDescriptions.Add(new PropertyGroupDescription("varType"));
        varCollectionview.View.Filter = new Predicate<object>(filter);
        varCollectionview.View.Refresh();
            }));

it seems that the View is noticed that the source is updated and deletes the sortdescriptions, but that happes delayed. All to do is add the sortdescription also delayed

CollectionView only sorting first time (when create viewmodel again it doesnt)

1 Answers1