It appears this is an issue with the way the multi-plot cursor updates the AxisValue property. While the data template is being constructed, the Window ancestor is not available, so the binding fails to evaluate. When the cursor updates the property value, the binding system discards the binding, rather than waiting until the ancestor can be resolved.
As a workaround, you can use a custom intermediary object to act as the target and the source for the ancestor and the cursor binding:
Code
public sealed class Intermediary : Control {
public static readonly DependencyProperty Sync1Property = DependencyProperty.Register( "Sync1", typeof( object ), typeof( Intermediary ), new PropertyMetadata( OnSyncPropertyChanged ) );
public static readonly DependencyProperty Sync2Property = DependencyProperty.Register( "Sync2", typeof( object ), typeof( Intermediary ), new PropertyMetadata( OnSyncPropertyChanged ) );
public Intermediary( ) { Visibility = Visibility.Collapsed; }
public object Sync1 {
get { return (object)GetValue( Sync1Property ); }
set { SetValue( Sync1Property, value ); }
}
public object Sync2 {
get { return (object)GetValue( Sync2Property ); }
set { SetValue( Sync2Property, value ); }
}
private static void OnSyncPropertyChanged( DependencyObject d, DependencyPropertyChangedEventArgs e ) {
DependencyProperty otherSyncProperty = e.Property == Sync2Property ? Sync1Property : Sync2Property;
d.SetValue( otherSyncProperty, e.NewValue );
}
}
XAML
<ni:Graph ...>
<ni:Graph.Children>
<ni:MultiPlotCursor x:Name="cursor" ... />
</ni:Graph.Children>
</ni:Graph>
<local:Intermediary x:Name="intermediary"
Sync1="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.MarkerXValue, Mode=TwoWay}"
Sync2="{Binding ElementName=cursor, Path=AxisValue, Mode=TwoWay}" />
Here, the binding from the cursor to the
~ Paul H
