New answers tagged add-in
Instead of using a Timer (which runs on a separate thread) how about using the inbuilt events: IActiveViewEvents.ViewRefreshed (start refresh) and then IActiveViewEvents.AfterDraw (finished refresh). If you listen for the AfterDraw with the drawphase esriViewDrawPhase.esriViewForeground or esriViewDrawPhase.esriViewAll (you might need to experiment a bit to ...
If you are using System.Timers.Timer or System.Threading.Timer, your code that is triggered by the timer occurs on a worker thread. This thread will not be marked STAThread and so can't use the SaveFileDialog. You could either use System.Windows.Forms.Timer, which is synchronous and on the main UI thread, or use Control.Invoke to run your code on the main ...
I think I have cracked it, after the delete statement I added mxDoc.UpdateContents(); which seems to have worked,
ArcGIS Pro currently does not support Python add-ins. There were no plans for a Python Add-in support in ArcGIS Pro. ArcGIS Pro has arcpy site package shipped though (you can author Python script tools). Your only option is ArcGIS Pro .NET SDK which is going to be released soon (it is in beta now).
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