Create new MaterialManagementModel and move canMaterialBeRemoved

Just like the QualityManagementModel, this class is intended to be used as proxy for the material management page in the preferences. I'm intending to move all relevant pyqtSlots from the material manager into this one. The advantage of this switch is that the material manager had no well-bounded scope and so tended to become a big mess of all sorts of functions. This one has a clear scope: serve as a proxy for the buttons you can press in the preferences screen for materials.

Contributes to issue CURA-6600.

cura/CuraApplication.py

@@ -85,6 +85,7 @@ from cura.Machines.Models.FirstStartMachineActionsModel import FirstStartMachine
 from cura.Machines.Models.GenericMaterialsModel import GenericMaterialsModel
 from cura.Machines.Models.GlobalStacksModel import GlobalStacksModel
 from cura.Machines.Models.MaterialBrandsModel import MaterialBrandsModel
+from cura.Machines.Models.MaterialManagementModel import MaterialManagementModel
 from cura.Machines.Models.MultiBuildPlateModel import MultiBuildPlateModel
 from cura.Machines.Models.NozzleModel import NozzleModel
 from cura.Machines.Models.QualityManagementModel import QualityManagementModel
@@ -1054,6 +1055,7 @@ class CuraApplication(QtApplication):
         qmlRegisterType(GenericMaterialsModel, "Cura", 1, 0, "GenericMaterialsModel")
         qmlRegisterType(MaterialBrandsModel, "Cura", 1, 0, "MaterialBrandsModel")
         qmlRegisterType(QualityManagementModel, "Cura", 1, 0, "QualityManagementModel")
+        qmlRegisterType(MaterialManagementModel, "Cura", 1, 5, "MaterialManagementModel")
 
         qmlRegisterType(DiscoveredPrintersModel, "Cura", 1, 0, "DiscoveredPrintersModel")
 

cura/Machines/MaterialManager.py

@@ -1,5 +1,6 @@
 # Copyright (c) 2019 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
+
 from collections import defaultdict
 import copy
 import uuid
@@ -7,19 +8,16 @@ from typing import Dict, Optional, TYPE_CHECKING, Any, List, cast
 
 from PyQt5.Qt import QTimer, QObject, pyqtSignal, pyqtSlot
 
-from UM.ConfigurationErrorMessage import ConfigurationErrorMessage
 from UM.Decorators import deprecated
 from UM.Logger import Logger
 from UM.Settings.ContainerRegistry import ContainerRegistry
-from UM.Settings.SettingFunction import SettingFunction
 from UM.Util import parseBool
-import cura.CuraApplication #Imported like this to prevent circular imports.
+import cura.CuraApplication  # Imported like this to prevent circular imports.
 from cura.Machines.ContainerTree import ContainerTree
 from cura.Settings.CuraContainerRegistry import CuraContainerRegistry
 
 from .MaterialNode import MaterialNode
 from .MaterialGroup import MaterialGroup
-from .VariantType import VariantType
 
 if TYPE_CHECKING:
     from UM.Settings.DefinitionContainer import DefinitionContainer
@@ -260,8 +258,8 @@ class MaterialManager(QObject):
         # Check if the material is active in any extruder train. In that case, the material shouldn't be removed!
         # In the future we might enable this again, but right now, it's causing a ton of issues if we do (since it
         # corrupts the configuration)
-        root_material_id = material_node.container.getMetaDataEntry("base_file")
+        root_material_id = material_node.base_file
-        ids_to_remove = [metadata.get("id", "") for metadata in CuraContainerRegistry.getInstance().findInstanceContainersMetadata(base_file=root_material_id)]
+        ids_to_remove = {metadata.get("id", "") for metadata in CuraContainerRegistry.getInstance().findInstanceContainersMetadata(base_file = root_material_id)}
 
         for extruder_stack in CuraContainerRegistry.getInstance().findContainerStacks(type = "extruder_train"):
             if extruder_stack.material.getId() in ids_to_remove:

cura/Machines/Models/MaterialManagementModel.py

@@ -0,0 +1,33 @@
+# Copyright (c) 2019 Ultimaker B.V.
+# Cura is released under the terms of the LGPLv3 or higher.
+
+from PyQt5.QtCore import QObject, pyqtSlot  # To allow the preference page proxy to be used from the actual preferences page.
+from typing import TYPE_CHECKING
+
+from cura.Settings.CuraContainerRegistry import CuraContainerRegistry  # To find the sets of materials belonging to each other, and currently loaded extruder stacks.
+
+if TYPE_CHECKING:
+    from cura.Machines.MaterialNode import MaterialNode
+
+##  Proxy class to the materials page in the preferences.
+#
+#   This class handles the actions in that page, such as creating new materials,
+#   renaming them, etc.
+class MaterialManagementModel(QObject):
+    ##  Can a certain material be deleted, or is it still in use in one of the
+    #   container stacks anywhere?
+    #
+    #   We forbid the user from deleting a material if it's in use in any stack.
+    #   Deleting it while it's in use can lead to corrupted stacks. In the
+    #   future we might enable this functionality again (deleting the material
+    #   from those stacks) but for now it is easier to prevent the user from
+    #   doing this.
+    #   \return Whether or not the material can be removed.
+    @pyqtSlot("QVariant", result = bool)
+    def canMaterialBeRemoved(self, material_node: "MaterialNode"):
+        container_registry = CuraContainerRegistry.getInstance()
+        ids_to_remove = {metadata.get("id", "") for metadata in container_registry.findInstanceContainersMetadata(base_file = material_node.base_file)}
+        for extruder_stack in container_registry.findContainerStacks(type = "extruder_train"):
+            if extruder_stack.material.getId() in ids_to_remove:
+                return False
+        return True

resources/qml/Preferences/Materials/MaterialsPage.qml

@@ -7,7 +7,7 @@ import QtQuick.Layouts 1.3
 import QtQuick.Dialogs 1.2
 
 import UM 1.2 as UM
-import Cura 1.0 as Cura
+import Cura 1.5 as Cura
 
 Item
 {
@@ -42,6 +42,11 @@ Item
         name: "cura"
     }
 
+    Cura.MaterialManagementModel
+    {
+        id: materialManagement
+    }
+
     function resetExpandedActiveMaterial()
     {
         materialListView.expandActiveMaterial(active_root_material_id)
@@ -147,7 +152,7 @@ Item
             id: removeMenuButton
             text: catalog.i18nc("@action:button", "Remove")
             iconName: "list-remove"
-            enabled: base.hasCurrentItem && !base.currentItem.is_read_only && !base.isCurrentItemActivated && base.materialManager.canMaterialBeRemoved(base.currentItem.container_node)
+            enabled: base.hasCurrentItem && !base.currentItem.is_read_only && !base.isCurrentItemActivated && materialManagement.canMaterialBeRemoved(base.currentItem.container_node)
 
             onClicked:
             {