Fast delete of many nodes causes an exception

Hi Jason,

I have a bug that was reported from my customers test team. They put 20 or more nodes on a diagram in a small region, so that they overlap each other. Than they start clicking and pressing the delete key very fast. After a while they get the following exception:

System.NullReferenceException: Object reference not set to an instance of an object. at Mindscape.WpfDiagramming.DiagramSurface.<>cDisplayClass2.b0() in c:\Experiment\WpfDiagrammingSource\Src\WpfDiagramming.Foundation\DiagramSurface.cs:line 479 at Mindscape.WpfDiagramming.DiagramSurface.SmartScrollTimer_Tick(Object sender, EventArgs e) in c:\Experiment\WpfDiagrammingSource\Src\WpfDiagramming.Foundation\DiagramSurface.cs:line 186 at System.Windows.Threading.DispatcherTimer.FireTick(Object unused) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)

Steps to reproduce:

1.) Take the QuickStart.FlowDiagrams solution 2.) Edit the diagram properties:

SnapLineDrawing="{StaticResource SnapLineDrawing}" />

3.) Start the sample and drop 20 nodes on the diagram so that they overlap 4.) Start clicking and pressing delete very fast

Thanks Markus

        <ms:DiagramSurface Name="ds" BorderThickness="0,1,1,1"
        Formatter="{StaticResource {x:Static ms:FlowDiagramStyles.GradientStyleFormatterKey}}"
        HorizontalSnapSpecifier="{ms:SnapToInterval 10}"
        VerticalSnapSpecifier="{ms:SnapToInterval 10}"
        ZoomMode="ControlMouseWheel"
        **DragAction="Pan"
        IsSmartScrollingEnabled="True"**
        SnapsToDevicePixels="True"
        CanModifyConnectionContent="False"
        CanRotateNodes="False"
        SelectionMode="Single"
        AllowNodeCollisions="True"
        AllowSegmentToNodeCollisions="True"
        VerticalScrollBarVisibility="Visible"
        HorizontalScrollBarVisibility="Visible"                       
        SnapLineDrawing="{StaticResource SnapLineDrawing}"
        />

Hello Markus

Thanks for pointing this out, this will be resolved in the next nightly build.

-Jason Fauchelle