FAQ: How to call SciChartSurface.SuspendUpdates() in a ViewModel

We know this breaks MVVM, but we recommend in really high performance scenarios, passing the SciChartSurface directly to your viewmodel and calling SciChartSurface.SuspendUpdates().

The interface that has SuspendUpdates() is actually ISuspendable. SciChartSurface implements ISuspendable.

// SciChartSurface implements ISciChartSurface and ISuspendable interfaces
public class SciChartSurface : ISciChartSurface, ISuspendable 
{
    // ... 

In order to not break testability of your ViewModels, we recommend you cast to ISuspendable before passing your SciChartSurface to a ViewModel. Then, you can call SuspendUpdates directly (on any thread) and you can still unit test your ViewModels.

Worked Example – Create Multi Pane Stock Charts example

1. Create a property in your chart pane ViewModel to hold the ISuspendable

    public abstract class BaseChartPaneViewModel : BaseViewModel, IChildPane
    {
        private ISuspendable _scs; 
        public ISuspendable Suspendable
        {
            get { return _scs; } 
            set { _scs = value; }
        }
   

2. Create an Attached Property to inject the SciChartSurface as ISuspendable

   public class Injector
   {
       public static readonly DependencyProperty PassSurfaceToViewModelProperty = DependencyProperty.RegisterAttached(
          "PassSurfaceToViewModel", typeof(bool), typeof(Injector), new PropertyMetadata(default(bool), OnPassSurfaceToViewModelPropertyChanged));
   
       private static void OnPassSurfaceToViewModelPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
       {
           var scs = d as SciChartSurface;
           if (scs == null || ((bool)e.NewValue) == false) return;
   
           scs.DataContextChanged += (s, arg) => UpdateProperty(scs, scs.DataContext as BaseChartPaneViewModel);
   
           UpdateProperty(scs, scs.DataContext as BaseChartPaneViewModel);
       }
   
       private static void UpdateProperty(SciChartSurface scs, BaseChartPaneViewModel vm)
       {
           if (vm == null) return;
           vm.Suspendable = scs;
       }
   
       public static void SetPassSurfaceToViewModel(DependencyObject element, ISuspendable value)
       {
           element.SetValue(PassSurfaceToViewModelProperty, value);
       }
   
       public static bool GetPassSurfaceToViewModel(DependencyObject element)
       {
           return (bool)element.GetValue(PassSurfaceToViewModelProperty);
       }        
   }
   

3. Set the attached property in your view. This even works inside SciChartGroup

   <s:SciChartGroup ItemsSource="{Binding ChartPaneViewModels}">
               <s:SciChartGroup.ItemTemplate>
                   <DataTemplate>
   
                       <!-- A lot has been omitted for brevity here. Just set the property on the SciChartSurface -->          
   
                       <s:SciStockChart multiPane:Injector.PassSurfaceToViewModel="True">
   

4. When the application starts, the SciChartSurface (or SciStockChart) will be passed to the ViewModel, cast to ISuspendable.

You can now call SuspendUpdates() directly 🙂