Deleting DWG Imports and their categories

Recent posts have looked at how to delete ImportInstance elements. This led to the question about how to get rid of those categories that are left behind and visible in the Visibility/Graphics and Object Styles dialog.

In some ways, import instances and family instances are quite similar. Revit stores a single definition of the family/import and then places one or more instances of the family/import in the model.

With the FamilyInstance class in the API we can get the FamilySymbol and from the FamilySymbol we can get the Family. ImportInstance has no such properties. But we can see from the status prompt & tooltip when these elements are selected that there is a similar hierarchy in both FamilyInstance and ImportInstance elements.

The solution is that if you want to delete both the import instances and the associated import categories, then the thing do do is delete the category, not just the instance.

This code builds a unique list of element id’s that represent the categories of imported elements.  Deleting the import category also deletes all instances of that import.

public void deleteImportCategories()
{
    Document doc = this.ActiveUIDocument.Document;   

    IList<ElementId> categoryIds = new List<ElementId>();

    foreach (ImportInstance ii in  new FilteredElementCollector(doc)
        .OfClass(typeof(ImportInstance))
        .Cast<ImportInstance>()
        .Where(i => i.IsLinked == false))
    {
        ElementId catId = ii.Category.Id;
        if (!categoryIds.Contains(catId))
            categoryIds.Add(catId);
    }

    using (Transaction t = new Transaction(doc,"Delete Import Categories"))
       {
        t.Start();
        doc.Delete(categoryIds);
        t.Commit();
    }
}