Only allow material assignment if we have available materials to assign. See #1222.

src/ifcblenderexport/blenderbim/bim/module/material/data.py

@@ -31,25 +31,33 @@ class Data:
 
     @classmethod
     def load_materials(cls):
+        cls.materials = {}
         cls.load_element("IfcMaterial", cls.materials)
 
     @classmethod
     def load_constituents(cls):
+        cls.constituent_sets = {}
+        cls.constituents = {}
         cls.load_element("IfcMaterialConstituent", cls.constituents)
         cls.load_element("IfcMaterialConstituentSet", cls.constituent_sets)
 
     @classmethod
     def load_layers(cls):
+        cls.layer_sets = {}
+        cls.layers = {}
         cls.load_element("IfcMaterialLayer", cls.layers)
         cls.load_element("IfcMaterialLayerSet", cls.layer_sets)
 
     @classmethod
     def load_profiles(cls):
+        cls.profile_sets = {}
+        cls.profiles = {}
         cls.load_element("IfcMaterialProfile", cls.profiles)
         cls.load_element("IfcMaterialProfileSet", cls.profile_sets)
 
     @classmethod
     def load_lists(cls):
+        cls.lists = {}
         cls.load_element("IfcMaterialList", cls.lists)
 
     @classmethod

src/ifcblenderexport/blenderbim/bim/module/material/operator.py

@@ -25,6 +25,7 @@ class AddMaterial(bpy.types.Operator):
         self.file = IfcStore.get_file()
         result = add_material.Usecase(self.file, {"Name": obj.name}).execute()
         obj.BIMObjectProperties.ifc_definition_id = result.id()
+        Data.load()
         return {"FINISHED"}
 
 
@@ -40,6 +41,7 @@ class RemoveMaterial(bpy.types.Operator):
             self.file, {"material": self.file.by_id(obj.BIMObjectProperties.ifc_definition_id)}
         ).execute()
         obj.BIMObjectProperties.ifc_definition_id = 0
+        Data.load()
         return {"FINISHED"}
 
 

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

@@ -39,6 +39,11 @@ class BIM_PT_object_material(Panel):
             Data.load(self.oprops.ifc_definition_id)
         self.product_data = Data.products[self.oprops.ifc_definition_id]
 
+        if not Data.materials:
+            row = self.layout.row()
+            row.label(text="No Materials Available")
+            return
+
         if self.product_data:
             if self.product_data["type"] == "IfcMaterialConstituentSet":
                 self.material_set_data = Data.constituent_sets[self.product_data["id"]]