WIP you can now start a fresh project with partial editing support. See #1222.

src/ifcblenderexport/blenderbim/bim/module/root/ui.py

@@ -1,6 +1,7 @@
 import bpy
 from bpy.types import Panel
 from blenderbim.bim.module.root.data import Data
+from blenderbim.bim.ifc import IfcStore
 
 class BIM_PT_class(Panel):
     bl_label = "IFC Class"
@@ -9,6 +10,10 @@ class BIM_PT_class(Panel):
     bl_region_type = "WINDOW"
     bl_context = "object"
 
+    @classmethod
+    def poll(cls, context):
+        return IfcStore.get_file()
+
     def draw(self, context):
         props = context.active_object.BIMObjectProperties
         if props.ifc_definition_id:
@@ -35,7 +40,10 @@ class BIM_PT_class(Panel):
             self.draw_class_dropdowns()
             row = self.layout.row(align=True)
             op = row.operator("bim.assign_class")
-            op.object_name = context.active_object.name
+            op.obj = context.active_object.name
+            op.ifc_class = bpy.context.scene.BIMProperties.ifc_class
+            op.predefined_type = bpy.context.scene.BIMProperties.ifc_predefined_type
+            op.userdefined_type = bpy.context.scene.BIMProperties.ifc_userdefined_type
 
     def draw_class_dropdowns(self):
         props = bpy.context.scene.BIMProperties