calculate materials checksum in a common method

src/blenderbim/blenderbim/bim/export_ifc.py

@@ -139,7 +139,7 @@ class IfcExporter:
 
     def has_changed_materials(self, obj: bpy.types.Object) -> bool:
         checksum = obj.data.BIMMeshProperties.material_checksum
-        return checksum != str([s.id() for s in tool.Geometry.get_styles(obj) if s])
+        return checksum != tool.Geometry.get_material_checksum(obj)
 
     def sync_object_placement(self, obj: bpy.types.Object) -> Union[ifcopenshell.entity_instance, None]:
         element = self.file.by_id(obj.BIMObjectProperties.ifc_definition_id)

src/blenderbim/blenderbim/tool/geometry.py

@@ -405,6 +405,10 @@ class Geometry(blenderbim.core.tool.Geometry):
             return "IfcExtrudedAreaSolid/IfcCircleProfileDef"
         return "IfcExtrudedAreaSolid/IfcArbitraryProfileDefWithVoids"
 
+    @classmethod
+    def get_material_checksum(cls, obj: bpy.types.Object) -> str:
+        return str([s.id() for s in cls.get_styles(obj) if s])
+
     @classmethod
     def get_mesh_checksum(cls, mesh: Union[bpy.types.Mesh, bpy.types.Curve]) -> str:
         data_bytes = b""
@@ -659,7 +663,7 @@ class Geometry(blenderbim.core.tool.Geometry):
 
     @classmethod
     def record_object_materials(cls, obj: bpy.types.Object) -> None:
-        obj.data.BIMMeshProperties.material_checksum = str([s.id() for s in cls.get_styles(obj) if s])
+        obj.data.BIMMeshProperties.material_checksum = cls.get_material_checksum(obj)
 
     @classmethod
     def record_object_position(cls, obj: bpy.types.Object) -> None: