I want to make independent point selections on multiple charts.

Hi there,

There’s nothing static in DataPointSelectionModifier or SciChartSurface that would share selected points between chart instances.

You do however declare a DependencyProperty in your custom class like this:

public class DataPointSelectionModifierExtention : DataPointSelectionModifier
{
    public ObservableCollection<DataPointInfo> SelectedPointMarkers2
    {
        get => (ObservableCollection<DataPointInfo>)GetValue(SelectedPointMakers2Property);
        set => SetValue(SelectedPointMakers2Property, value);
    }
    public static readonly DependencyProperty SelectedPointMakers2Property =
        DependencyProperty.Register(
            nameof(SelectedPointMarkers2),
            typeof(ObservableCollection<DataPointInfo>),
            typeof(DataPointSelectionModifierExtention),
            new PropertyMetadata(new ObservableCollection<DataPointInfo>())); // HERE

This unknowingly creates a single instance of ObservableCollection<DataPointInfo> and assigns it as the default value of DataPointSelectionModifierExtention.SelectedPointMarkers2. So if you are getting points shared between charts this could be the reason.

What I suggest:

• Never set an instance of a reference type as the default value in a dependency property (see here for more info)
• Instead, use this.SetCurrentValue(SelectedPointMakers2Property, new ObservableCollection<DataPointInfo>()); to set the value of the dependency property to a new ObservableCollection. The best place to do this would be your DataPointSelectionModifierExtention constructor

Try that. Remove the default value and set it later in the ctor so you have one ObservableCollection instance per DataPointSelectionModifierExtention instance

Best regards,
andrew