Sorting an ObservableCollection after editing a property of an item

Question

I'm trying to bind an ObservableCollection<T> to a DataGrid in WPF. Below the DataGrid, there are fields to edit the currently selected item from the DataGridlike so:

So the generic T of the ObservableCollection<T> has the following properties: - Title (Überschrift) - Description (Beschreibung) - Path (Pfad)

and it also has a property Reihenfolge which means Order.

With the yellow arrows, I want to be able to modify the order of the entries.

Unfortunately, the ObservableCollection doesn't have an OrderBy-method...

I've tried the following:

In XAML I have defined a CollectionViewSource like this:

<CollectionViewSource Source="{Binding Bilder}" x:Key="Pictures">
    <CollectionViewSource.SortDescriptions>
        <scm:SortDescription PropertyName="Reihenfolge" />
    </CollectionViewSource.SortDescriptions>
</CollectionViewSource>

And I have binded the DataGrid to this CollectionViewSource

<DataGrid Grid.Column="0" Grid.Row="1"
          Name="PictureDataGrid"  
          ItemsSource="{Binding Source={StaticResource Pictures}}"
          AutoGenerateColumns="False" 
          IsReadOnly="True" 
          CanUserAddRows="false" 
          SelectedItem="{Binding SelectedBild}"  
          HorizontalAlignment="Stretch" 
          VerticalAlignment="Stretch">
 ...

In the ViewModel, I have these properties:

public ObservableCollection<BildNotifiableModel> Bilder { get; set; }
public BildNotifiableModel SelectedBild { get; set; }

and two methods which are called with DelegateCommands that update the order

 private void MoveSeiteUp()
 {
     const int smallestReihenfolge = 1;
     if (this.SelectedBild.Reihenfolge > smallestReihenfolge) {
            var bildToSwapReihenfolgeWith = this.Bilder.Single(b => b.Reihenfolge == this.SelectedBild.Reihenfolge - 1);
            this.SelectedBild.Reihenfolge--;
            bildToSwapReihenfolgeWith.Reihenfolge++;

            RaisePropertyChanged(nameof(this.Bilder));
        }
    }

    private void MoveSeiteDown()
    {
        if (this.SelectedBild.Reihenfolge < MaxAllowedImages) {
            var bildToSwapReihenfolgeWith = this.Bilder.Single(b => b.Reihenfolge == this.SelectedBild.Reihenfolge + 1);
            this.SelectedBild.Reihenfolge++;
            bildToSwapReihenfolgeWith.Reihenfolge--;

            RaisePropertyChanged(nameof(this.Bilder));
        }
    }

The order gets updated correctly, but unfortunately, the view doesn't reflect the changes... only after closing and reopening the view, the entries in the DataGrid are in the correct order.

What am I doing wrong here?
How can I make the DataGrid update, when changing the order?

Thanks in advance

Instead of providing a translation of all your code, why not post a translated version here? — ChristianMurschall, Sep 20 '18 at 11:37
To answer your question: [check this out](https://stackoverflow.com/a/5256827/4634044) — ChristianMurschall, Sep 20 '18 at 11:44
The `ObservableCollection` class has a [Move](https://learn.microsoft.com/en-us/dotnet/api/system.collections.objectmodel.observablecollection-1.move?view=netframework-4.7.2) method which you should be able to use here. — mm8, Sep 20 '18 at 12:25
@ChristianMurschall this helped, thank you! If you add this as an answer, I'll accept it :) — xeraphim, Sep 24 '18 at 06:58

Ackdari · Answer 1 · 2018-09-20T11:27:13.943

I think the problem is that the CollectionView doesn't listen for the PropertyChanged-Events from its elements and also RaisePropertyChanged(nameof(this.Bilder)); dosen't work because the CollectionView is not really changed.

I would recomend to create the CollectionView in code via CollectionViewSource.GetDefaultView(list). So you can control the CollectionView from your model and call ICollectionView.Refresh if needed.

score 0 · Answer 2 · answered Sep 20 '18 at 11:43

In your Methods, create a new Collection and add it to "Bilder". Just raising the PropertyChanged will execute an evaluation for referential equality. If it is the same - which it will be, if you just move items inside around - it will not update the DataGrid.

If you are not using the ObservableCollections attributes, like automatically updates, when items are added or removed, you might also change it to a "normal" List.

private void MoveSeiteUp()
{
 const int smallestReihenfolge = 1;
 if (this.SelectedBild.Reihenfolge > smallestReihenfolge) {
        var bildToSwapReihenfolgeWith = this.Bilder.Single(b => b.Reihenfolge == this.SelectedBild.Reihenfolge - 1);
        this.SelectedBild.Reihenfolge--;
        bildToSwapReihenfolgeWith.Reihenfolge++;

        this.Bilder = new ObservableCollection<BildNotifiableModel> (this.Bilder);

        RaisePropertyChanged(nameof(this.Bilder));
    }
}

private void MoveSeiteDown()
{
    if (this.SelectedBild.Reihenfolge < MaxAllowedImages) {
        var bildToSwapReihenfolgeWith = this.Bilder.Single(b => b.Reihenfolge == this.SelectedBild.Reihenfolge + 1);
        this.SelectedBild.Reihenfolge++;
        bildToSwapReihenfolgeWith.Reihenfolge--;

        this.Bilder = new ObservableCollection<BildNotifiableModel> (this.Bilder);

        RaisePropertyChanged(nameof(this.Bilder));
    }
}

Sorting an ObservableCollection after editing a property of an item

2 Answers2