Replaced hack for setting extruders with more robust setter

CURA-1263

cura/Settings/ExtruderManager.py

@@ -150,6 +150,18 @@ class ExtruderManager(QObject):
         if changed:
             self.extrudersChanged.emit(machine_id)
 
+    def registerExtruder(self, extruder_train, machine_id):
+        changed = False
+
+        if machine_id not in self._extruder_trains:
+            self._extruder_trains[machine_id] = {}
+            changed = True
+        if extruder_train:
+            self._extruder_trains[machine_id][extruder_train.getMetaDataEntry("position")] = extruder_train
+            changed = True
+        if changed:
+            self.extrudersChanged.emit(machine_id)
+
     ##  Creates a container stack for an extruder train.
     #
     #   The container stack has an extruder definition at the bottom, which is

plugins/3MFReader/ThreeMFWorkspaceReader.py

@@ -301,11 +301,11 @@ class ThreeMFWorkspaceReader(WorkspaceReader):
                         quality_changes_index = stack.getContainerIndex(old_container)
                         stack.replaceContainer(quality_changes_index, container)
 
-        # TODO: This is nasty hack; this should be made way more robust (setter?)
-        if global_stack.getId() not in ExtruderManager.getInstance()._extruder_trains:
-            ExtruderManager.getInstance()._extruder_trains[global_stack.getId()] = {}
         for stack in extruder_stacks:
-            ExtruderManager.getInstance()._extruder_trains[global_stack.getId()][stack.getMetaDataEntry("position")] = stack
+            ExtruderManager.getInstance().registerExtruder(stack, global_stack.getId())
+        else:
+            # Machine has no extruders, but it needs to be registered with the extruder manager.
+            ExtruderManager.getInstance().registerExtruder(None, global_stack.getId())
 
         Logger.log("d", "Workspace loading is notifying rest of the code of changes...")
         # Notify everything/one that is to notify about changes.

plugins/3MFReader/WorkspaceDialog.qml

@@ -128,7 +128,7 @@ UM.Dialog
                 width: parent.width
                 height: visible ? 25 : 0
                 text: catalog.i18nc("@info:tooltip", "How should the conflict in the material(s) be resolved?")
-                visible: false #manager.materialConflict
+                visible: false //manager.materialConflict
                 Row
                 {
                     width: parent.width