Why I can't use WhereElementIsElementType and WhereElementIsNotElementType in the same class

[duongphong29]

Hi!

I am trying to get FamilySymbols and FamilyInstances of the same category. Here is my code:

            ElementId targetCategoryId = elementList.ElementAt(0).Category.Id;
            FilteredElementCollector collection = new FilteredElementCollector(doc);
            ElementCategoryFilter filterCategory = new ElementCategoryFilter(targetCategoryId);
            IList<Element> allFamilyInstances = collection.WherePasses(filterCategory).WhereElementIsNotElementType().ToElements();
            IList<Element> targetFamilySymbols = collection.WherePasses(filterCategory).WhereElementIsElementType().ToElements();

The problem is the list allFamilyInstaces give me exactly what I want but targetFamilySymbols list gives me zero item.

When I move the line of code 

            IList<Element> targetFamilySymbols = collection.WherePasses(filterCategory).WhereElementIsElementType().ToElements();

to before the allFamilyInstances list. The result is vice versa, targetFamilySymbols gives all family symbols but allFamilyInstaces gives me none.

Can someone explain for me why? And how can I deal with this? Thank you

[jeremy_tammik · Accepted solution]

Every subsequent filter that you apply is added to all the previous filters as a logical AND.

So, if you apply two mutually exclusive filters, one after the other, the result will always be void.

https://thebuildingcoder.typepad.com/blog/2021/02/splits-persona-collector-region-tag-modification.h...

[duongphong29]

Oh, I understand, thank you