Fix the usage of protected variables in material models

cura/Machines/Models/BaseMaterialsModel.py

@@ -12,10 +12,9 @@ def getAvailableMaterials(extruder_position: Optional[int] = None):
     from cura.CuraApplication import CuraApplication
     machine_manager = CuraApplication.getInstance().getMachineManager()
     extruder_manager = CuraApplication.getInstance().getExtruderManager()
+    material_manager = CuraApplication.getInstance().getMaterialManager()
 
-    material_manager = CuraApplication.getInstance()._material_manager
-
-    active_global_stack = machine_manager._global_container_stack
+    active_global_stack = machine_manager.activeMachine
     extruder_stack = extruder_manager.getActiveExtruderStack()
     if extruder_position is not None:
         if active_global_stack is not None:

cura/Machines/Models/BrandMaterialsModel.py

@@ -37,7 +37,7 @@ class BrandMaterialsModel(ListModel):
         from cura.CuraApplication import CuraApplication
         self._machine_manager = CuraApplication.getInstance().getMachineManager()
         extruder_manager = CuraApplication.getInstance().getExtruderManager()
-        material_manager = CuraApplication.getInstance()._material_manager
+        material_manager = CuraApplication.getInstance().getMaterialManager()
 
         self._machine_manager.globalContainerChanged.connect(self._update)
         extruder_manager.activeExtruderChanged.connect(self._update)

cura/Machines/Models/GenericMaterialsModel.py

@@ -12,7 +12,7 @@ class GenericMaterialsModel(BaseMaterialsModel):
         from cura.CuraApplication import CuraApplication
         self._machine_manager = CuraApplication.getInstance().getMachineManager()
         self._extruder_manager = CuraApplication.getInstance().getExtruderManager()
-        self._material_manager = CuraApplication.getInstance()._material_manager
+        self._material_manager = CuraApplication.getInstance().getMaterialManager()
 
         self._machine_manager.globalContainerChanged.connect(self._update)
         self._extruder_manager.activeExtruderChanged.connect(self._update)

cura/Machines/Models/MaterialManagementModel.py

@@ -53,7 +53,7 @@ class MaterialManagementModel(ListModel):
         self._container_registry = CuraApplication.getInstance().getContainerRegistry()
         self._machine_manager = CuraApplication.getInstance().getMachineManager()
         extruder_manager = CuraApplication.getInstance().getExtruderManager()
-        material_manager = CuraApplication.getInstance()._material_manager
+        material_manager = CuraApplication.getInstance().getMaterialManager()
 
         self._machine_manager.globalContainerChanged.connect(self._update)
         extruder_manager.activeExtruderChanged.connect(self._update)