We are able to reproduce the reported issue "SfDiagram throws exeception while clicking on background", however it seems to be WinRT framework issue (Exception in VisualTreeHelper), but unable to predict the exact root cause or the scenario. However, we have considered this issue as a defect and we have logged an issue report to fix this. This fix will be available in our future WinRT service pack releases.
Please let us if you have any concerns,
I'm having the same problem, any workarounds?
To avoid the defect”SfDiagram throws exception while clicking on background”, Please set ManipulationMode of ScrollViewer inside SfDiagram to ‘None’. We have created a simple sample to resolve the reported issue. Please refer to the sample from the attachment.
This sample is just to avoid the exception. As an effect of this, zooming and panning operation cannot not be performed on SfDiagram with touch gesture.
We have fixed this reported issue by using alternative way to find the Parent of Dependency Object instead of using VisualTreeHelper.GetParent (dobj). This fix will be available in our future WinRT service pack releases.
Please let us know if you have any questions about this.