TreeDataGrid does not update when model properties change

[SuperJMN]

Describe the bug Given an underlying model that implements INotifyPropertyChanged, the TreeDataGrid doesn't update when the model is updated.

To Reproduce

• For convenience, I've created a repo ready to test the issue:

https://github.com/SuperJMN-Tutorials/TreeDataGrid-Out-Of-Sync

If you want to do it yourself:

1. Create a new MVVM application.
2. Add the TreeDataGrid package.
3. Add this code to MainViewModel.

public class MainWindowViewModel : ViewModelBase
{
    public MainWindowViewModel()
    {
        var collection = new ObservableCollection<Model>();
        var model = new Model("Hello!");
        collection.Add(model);
        Source = new FlatTreeDataGridSource<Model>(collection)
        {
            Columns =
            {
                new TextColumn<Model, string>("Text", x => x.Text),
            }
        };

        Observable.Timer(TimeSpan.FromSeconds(2))
            .ObserveOn(RxApp.MainThreadScheduler)
            .Subscribe(_ => model.Text = "How are you?");
    }

    public FlatTreeDataGridSource<Model> Source { get; }
}

public class Model : ViewModelBase
{
    private string text;

    public Model(string text)
    {
        Text = text;
    }

    public string Text
    {
        get => text;
        set => this.RaiseAndSetIfChanged(ref text, value);
    }
}

4. Add this code to MainWindow.axaml:

 <TreeDataGrid Source="{Binding Source}" />

5. Run the project.

Expected behavior After 2 seconds, the data in the DataGrid should display "How are you?". However, it shows the initial text "Hello".

NOTES Interestingly enough, the TreeDataGrid starts to behave correctly when you click the column header. It seems that sorting a column makes it update.

Desktop (please complete the following information):

• OS: Windows 11

Additional context Avalonia 0.10.18.

[maxkatz6]

@grokys @Takoooooo

[CShark]

For anyone looking for a workaround - some reflection magic on private methods does allow to refresh the cells - namely calling CollectionChanged on the HierarchicalRows-Instance. You'll have to adjust the type though to match your HierarchicalTreeDataGridSource. In my case it was enough to call it every time the selection changes.

var rows = (HierarchicalRows<Entry>)EntriesTree.GetType()
    .GetMethod("GetOrCreateRows", BindingFlags.NonPublic | BindingFlags.Instance)
    .Invoke(EntriesTree, null);
var evt = (NotifyCollectionChangedEventHandler)rows.GetType().GetField("CollectionChanged",
    BindingFlags.NonPublic | BindingFlags.Instance)
    .GetValue(rows);

if (evt != null) {
    foreach (var handler in evt.GetInvocationList()) {
        handler.Method.Invoke(handler.Target,
            new object[]
                { rows, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset) });
    }
}

[boomer41]

Any update on this one? This makes the grid unusable when relying on INotifyPropertyChanged for the data.

[boomer41]

@SuperJMN

So, I went on and went to debug the missing IPropertyChanged subscription. Turns out, in v10, the TreeDataGridCell does indeed not subscribe.

However, this issue is already fixed in the latest master branch for v11 by commit 58394adb346e3472aae114053002d8b0639ae755 "Implement cell editing for text cells."

When adding the following code to the sample project on v11 to the Country model's constructor, we can observe the desired effect. I also made the model a ReactiveObject for convenience.

The columns refresh as expected. Now just to wait until v11 :)

            Task.Run(async () =>
            {
                while (true)
                {
                    await Task.Delay(TimeSpan.FromSeconds(1));

                    Dispatcher.UIThread.Post(() =>
                    {
                        Name += "1";
                        this.RaisePropertyChanged(nameof(Name));
                    });
                }
            });

[boomer41]

~~Okay, there STILL is a bug in the latest v11... The changed value only gets rendered every second property changed event. :(~~

EDIT: Was my fault. Works as intended.

[alexandrehtrb]

This problem still happens for me with a TextColumn; my workaround was to use a TemplatedColumn...