FilteredElementCollector only works sporadically when collecting ViewSheet

[Anonymous]

I have a plugin that contains the following code snippet

var document = commandData.Application.ActiveUIDocument.Document;
var collector = new FilteredElementCollector(document);
var views = collector.OfClass(typeof(ViewSheet)).ToElements().Cast<ViewSheet>();

Testing against the rac_basic_sample_revit project that comes supplied with Revit 2018.2, I sometimes get six valid ViewSheets returned, as expected, and other times I just get six nulls.  I get similar unpredictable results querying other types.

Can anybody shed any light on to what I may be doing wrongly?

[jeremytammik]

Nope.

Never heard of such a problem.

The filtered element collectors seem to be completely reliable in all cases, as far as I can tell.

By the way, you can eliminate the call to `ToElements`, it does absolutely nothing except waste time and effort.

Cheers,

Jeremy

[Anonymous]

Thanks.

I've tried refactoring the code as so:

var collector = new FilteredElementCollector(document);

var views = collector.OfClass(typeof(ViewSheet));

foreach (var element in views)
{
    var view = element as ViewSheet;
    ...
}           

But iterating the views result gives an immediate exception:

Autodesk.Revit.Exceptions.InternalException
  HResult=0x80131500
  Message=A managed exception was thrown by Revit or by one of its external applications.
  Source=RevitAPI
  StackTrace:
   at Autodesk.Revit.DB.FilteredElementCollector.GetFilteredElementCollectorIterator()
   at Autodesk.Revit.DB.DocumentExtensions.GetViewSheets(Document _document) 

[jeremytammik]

Your code is presumably running outside a valid Revit API context:

http://thebuildingcoder.typepad.com/blog/2015/12/external-event-and-10-year-forum-anniversary.html#2

Cheers,

Jeremy

[Anonymous]

Thanks,

I did think it was something like that, but it still failed even when that was the entirety of an ExternalCommand Execute method.

After a bit more headscratching, I eventually tracked down the culprit to a bit of UI code that had been introduced that defined a custom AssemblyResolve function - removing that seems to have everything working consistently - I can only assume it was causing Revit to fail to resolve one of its own assemblies under certain circumstances