Polygon and Polyline Points binding problem

[DannyVlasenko]

Avalonia 0.9.3

Xaml:

<Polygon Fill="Red" Points="{Binding DeltaPoints}"/>
<Polyline Stroke="Blue" Points="{Binding DeltaPoints}"/>

C#:

private readonly ReadOnlyObservableCollection<Avalonia.Point> _deltaPoints;
public ReadOnlyObservableCollection<Avalonia.Point> DeltaPoints => _deltaPoints;
private SourceList<Avalonia.Point> _pointsD;

_pointsD = new SourceList<Avalonia.Point>();
            _pointsD.Add(new Avalonia.Point(123, 45));
            _pointsD.Add(new Avalonia.Point(45, 45));
           ...
            _pointsD.Connect()
                .ObserveOn(RxApp.MainThreadScheduler)
                .Bind(out _deltaPoints)
                .Subscribe();

These bindings work only for the initial points collection. All dynamically added points change neither Polygon nor Polyline image. Binding of the same collection to a ListBox works well.

[Gillibald]

Had a quick look at the source and it looks like the geometries are not invalidated when the list of points changes. Should be easy to fix.

This will only update the rendering when the Points property changes and will not listen to collection changes.

[grokys]

Note that this is the same on WPF if I remember correctly: https://stackoverflow.com/questions/13643054/polyline-bound-to-observablelistpoint-doesnt-refresh

[DannyVlasenko]

        private void OnPointsChanged(Points newValue)
        {
            _pointsObserver?.Dispose();
            _pointsObserver = newValue?.ForEachItem(
                _ => InvalidateGeometry(),
                _ => InvalidateGeometry(),
                InvalidateGeometry,true);
        }

InvalidateGeometry isn't called for both add and remove operations on collection, still can't figure out why. Tried to switch to weak subscription, with no effect. _pointsD.Add only comes to OnEvent of WeakListener of ListBox

[TheSwerik]

So is this fixed? Or is there a workaround?

[Wally-Young]

Same problem，look forward to fix

[Wally-Young]

Is there any way to create a dynamic line

[Aperture-Electronic]

I rewrote an implementation of my own that uses the AvaloniaList to detect the event of an item update and update a Guid object. The Guid object is set to AffectsGeometry so that the Geometry can be updated automatically.

The code be like

public class VertexWire : Shape
{
    public static readonly DirectProperty<VertexWire, AvaloniaList<Point>> PointsProperty =
        AvaloniaProperty.RegisterDirect<VertexWire, AvaloniaList<Point>>(nameof(Points),
            (e) => e.Points);

    public static readonly DirectProperty<VertexWire, Guid> PointsGuidProperty =
        AvaloniaProperty.RegisterDirect<VertexWire, Guid>(nameof(PointsGuid),
            (e) => e.PointsGuid,
            (e, v) => e.PointsGuid = v);

    private AvaloniaList<Point> points = new();
    private Guid pointsGuid = Guid.Empty;

    public AvaloniaList<Point> Points
    {
        get => points;
    }

    public Guid PointsGuid
    {
        get => pointsGuid;
        set => SetAndRaise(PointsGuidProperty, ref pointsGuid, value);
    }

    static VertexWire()
    {
        StrokeThicknessProperty.OverrideDefaultValue<VertexWire>(1);
        AffectsGeometry<VertexWire>(PointsGuidProperty);
    }

    public VertexWire()
    {
        points.CollectionChanged += OnPointsChanged;
    }

    private void OnPointsChanged(object? sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        // Update the points guid to let the geometry renderer update
        PointsGuid = Guid.NewGuid();
    }

    protected override Geometry CreateDefiningGeometry()
        => new PolylineGeometry(Points, false);
}