Is call of Dispatcher in SvgDrawingCanvas necessary?

I can’t reproduce it in isolated small project, but in big WPF-application some svg-icons crashes in SvgDrawingCanvas.UnloadDiagrams() on Dispatcher.Invoke with “Cannot perform this operation while dispatcher processing is suspended.” exception in Main (UI) Thread. This trouble reproduces every time. I suppose it relates from call stack.

This is call stack of this crash:

>	SharpVectors.Runtime.Wpf.dll!SharpVectors.Runtime.SvgDrawingCanvas.UnloadDiagrams() Line 267	C#
 	SharpVectors.Converters.Wpf.dll!SharpVectors.Converters.SvgViewbox.OnUnloadDiagram() Line 1202	C#
 	SharpVectors.Converters.Wpf.dll!SharpVectors.Converters.SvgViewbox.OnLoadDrawing(System.Windows.Media.DrawingGroup drawing) Line 1183	C#
 	SharpVectors.Converters.Wpf.dll!SharpVectors.Converters.SvgViewbox.OnSettingsChanged() Line 950	C#
 	SharpVectors.Converters.Wpf.dll!SharpVectors.Converters.SvgViewbox.OnSourceChanged(System.Windows.DependencyObject obj, System.Windows.DependencyPropertyChangedEventArgs args) Line 1330	C#
 	WindowsBase.dll!System.Windows.DependencyObject.OnPropertyChanged(System.Windows.DependencyPropertyChangedEventArgs e)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.OnPropertyChanged(System.Windows.DependencyPropertyChangedEventArgs e)	Unknown
 	WindowsBase.dll!System.Windows.DependencyObject.NotifyPropertyChange(System.Windows.DependencyPropertyChangedEventArgs args)	Unknown
 	WindowsBase.dll!System.Windows.DependencyObject.UpdateEffectiveValue(System.Windows.EntryIndex entryIndex, System.Windows.DependencyProperty dp, System.Windows.PropertyMetadata metadata, System.Windows.EffectiveValueEntry oldEntry, ref System.Windows.EffectiveValueEntry newEntry, bool coerceWithDeferredReference, bool coerceWithCurrentValue, System.Windows.OperationType operationType)	Unknown
 	PresentationFramework.dll!System.Windows.StyleHelper.ApplyTemplatedParentValue(System.Windows.DependencyObject container, MS.Internal.FrameworkObject child, int childIndex, ref MS.Utility.FrugalStructList<System.Windows.ChildRecord> childRecordFromChildIndex, System.Windows.DependencyProperty dp, System.Windows.FrameworkElementFactory templateRoot)	Unknown
 	PresentationFramework.dll!System.Windows.StyleHelper.InvalidatePropertiesOnTemplateNode(System.Windows.DependencyObject container, MS.Internal.FrameworkObject child, int childIndex, ref MS.Utility.FrugalStructList<System.Windows.ChildRecord> childRecordFromChildIndex, bool isDetach, System.Windows.FrameworkElementFactory templateRoot)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkTemplate.InvalidatePropertiesOnTemplate(System.Windows.DependencyObject container, object currentObject)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkTemplate.HandleBeforeProperties(object createdObject, ref System.Windows.DependencyObject rootObject, System.Windows.DependencyObject container, System.Windows.FrameworkElement feContainer, System.Windows.Markup.INameScope nameScope)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadOptimizedTemplateContent.AnonymousMethod__2(object sender, System.Xaml.XamlObjectEventArgs args)	Unknown
 	System.Xaml.dll!System.Xaml.XamlObjectWriter.OnBeforeProperties(object value)	Unknown
 	System.Xaml.dll!System.Xaml.XamlObjectWriter.Logic_CreateAndAssignToParentStart(MS.Internal.Xaml.Context.ObjectWriterContext ctx)	Unknown
 	System.Xaml.dll!System.Xaml.XamlObjectWriter.WriteEndObject()	Unknown
 	System.Xaml.dll!System.Xaml.XamlWriter.WriteNode(System.Xaml.XamlReader reader)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadTemplateXaml(System.Xaml.XamlReader templateReader, System.Xaml.XamlObjectWriter currentWriter)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadTemplateXaml(System.Xaml.XamlObjectWriter objectWriter)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadOptimizedTemplateContent(System.Windows.DependencyObject container, System.Windows.Markup.IComponentConnector componentConnector, System.Windows.Markup.IStyleConnector styleConnector, System.Collections.Generic.List<System.Windows.DependencyObject> affectedChildren, System.Windows.UncommonField<System.Collections.Hashtable> templatedNonFeChildrenField)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadContent(System.Windows.DependencyObject container, System.Collections.Generic.List<System.Windows.DependencyObject> affectedChildren)	Unknown
 	PresentationFramework.dll!System.Windows.StyleHelper.ApplyTemplateContent(System.Windows.UncommonField<System.Collections.Specialized.HybridDictionary[]> dataField, System.Windows.DependencyObject container, System.Windows.FrameworkElementFactory templateRoot, int lastChildIndex, System.Collections.Specialized.HybridDictionary childIndexFromChildID, System.Windows.FrameworkTemplate frameworkTemplate)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkTemplate.ApplyTemplateContent(System.Windows.UncommonField<System.Collections.Specialized.HybridDictionary[]> templateDataField, System.Windows.FrameworkElement container)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.ApplyTemplate()	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize)	Unknown
 	PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.Grid.MeasureOverride(System.Windows.Size constraint)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize)	Unknown
 	PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.Border.MeasureOverride(System.Windows.Size constraint)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize)	Unknown
 	PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.Border.MeasureOverride(System.Windows.Size constraint)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize)	Unknown
 	PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.Grid.MeasureCell(int cell, bool forceInfinityV)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.Grid.MeasureCellsGroup(int cellsHead, System.Windows.Size referenceSize, bool ignoreDesiredSizeU, bool forceInfinityV, out bool hasDesiredSizeUChanged)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.Grid.MeasureCellsGroup(int cellsHead, System.Windows.Size referenceSize, bool ignoreDesiredSizeU, bool forceInfinityV)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.Grid.MeasureOverride(System.Windows.Size constraint)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize)	Unknown
 	PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize)	Unknown
 	PresentationFramework.dll!MS.Internal.Helper.MeasureElementWithSingleChild(System.Windows.UIElement element, System.Windows.Size constraint)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.ContentPresenter.MeasureOverride(System.Windows.Size constraint)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize)	Unknown
 	PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.Border.MeasureOverride(System.Windows.Size constraint)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize)	Unknown
 	PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.Control.MeasureOverride(System.Windows.Size constraint)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize)	Unknown
 	PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize)	Unknown
 	PresentationFramework.dll!MS.Internal.Helper.MeasureElementWithSingleChild(System.Windows.UIElement element, System.Windows.Size constraint)	Unknown
 	PresentationFramework.dll!System.Windows.Controls.ContentPresenter.MeasureOverride(System.Windows.Size constraint)	Unknown
 	PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize)	Unknown
 	PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize)	Unknown
 	PresentationCore.dll!System.Windows.ContextLayoutManager.UpdateLayout()	Unknown
 	PresentationCore.dll!System.Windows.ContextLayoutManager.UpdateLayoutCallback(object arg)	Unknown
 	PresentationCore.dll!System.Windows.Media.MediaContext.InvokeOnRenderCallback.DoWork()	Unknown
 	PresentationCore.dll!System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks()	Unknown
 	PresentationCore.dll!System.Windows.Media.MediaContext.RenderMessageHandlerCore(object resizedCompositionTarget)	Unknown
 	PresentationCore.dll!System.Windows.Media.MediaContext.RenderMessageHandler(object resizedCompositionTarget)	Unknown
 	WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)	Unknown
 	WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, System.Delegate callback, object args, int numArgs, System.Delegate catchHandler)	Unknown
 	WindowsBase.dll!System.Windows.Threading.DispatcherOperation.InvokeImpl()	Unknown
 	WindowsBase.dll!System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(object state)	Unknown
 	WindowsBase.dll!MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(object obj)	Unknown
 	mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)	Unknown
 	mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)	Unknown
 	mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state)	Unknown
 	WindowsBase.dll!MS.Internal.CulturePreservingExecutionContext.Run(MS.Internal.CulturePreservingExecutionContext executionContext, System.Threading.ContextCallback callback, object state)	Unknown
 	WindowsBase.dll!System.Windows.Threading.DispatcherOperation.Invoke()	Unknown
 	WindowsBase.dll!System.Windows.Threading.Dispatcher.ProcessQueue()	Unknown
 	WindowsBase.dll!System.Windows.Threading.Dispatcher.WndProcHook(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled)	Unknown
 	WindowsBase.dll!MS.Win32.HwndWrapper.WndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled)	Unknown
 	WindowsBase.dll!MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o)	Unknown
 	WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)	Unknown
 	WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, System.Delegate callback, object args, int numArgs, System.Delegate catchHandler)	Unknown
 	WindowsBase.dll!System.Windows.Threading.Dispatcher.LegacyInvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs)	Unknown
 	WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam)	Unknown
 	[Native to Managed Transition]	
 	[Managed to Native Transition]	
 	WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame frame)	Unknown
 	WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrame(System.Windows.Threading.DispatcherFrame frame)	Unknown
 	PresentationFramework.dll!System.Windows.Application.RunDispatcher(object ignore)	Unknown
 	PresentationFramework.dll!System.Windows.Application.RunInternal(System.Windows.Window window)	Unknown
 	PresentationFramework.dll!System.Windows.Application.Run(System.Windows.Window window)	Unknown
 	PresentationFramework.dll!System.Windows.Application.Run()	Unknown
 	Integral.RailwayEditor.Shell.exe!Integral.RailwayEditor.Shell.App.Main()	Unknown

Probably it occurs in cases like this: http://apaers.com/wpf-error-cannot-perform-operation-while-dispatcher-processing-is-suspended/

If I just remove this Invoke with empty action all works fine and I can’t find any troubles with svg rendering. 😃 Is this invoke necessary? For what it needs?

[Kozinaka]

I’ve checked it. No exceptions and visible troubles in both cases. All my icons displays correct: from SvgImage directly in XAML and from static binding to result of SvgImage.CreateDrawing() as ImageSource.

        public void UnloadDiagrams()
        {
            _offsetX = 0;
            _offsetY = 0;
            _bounds  = new Rect(0, 0, 1, 1);

            _wholeDrawing = null;

            _displayTransform = Transform.Identity;

            this.ClearVisuals();
            this.ClearDrawings();

            this.InvalidateMeasure();
            this.UpdateLayout();

            //this.Dispatcher.BeginInvoke(System.Windows.Threading.DispatcherPriority.Render, EmptyDelegate);
        }

[Kozinaka]

Okay! I got it!