Remove double call of _onGlobalContainerChanged and activeExtruderChanged on switching

When switching printers, it would first emit the global container changed signal which connects to _onGlobalContainerChanged, then update stuff in the extruder manager, then manually call _onGlobalContainerChanged again to update some other stuff with the new data from the extruder manager. This was prohibitively expensive, so this prevents that.
Another double or triple emit of the activeExtruderChanged was removed in the extruder manager when creating the extruders for a printer: It would first set the extruder number to 0, possibly emitting the signal, then emit the signal just to be sure since the extruder itself changed (rather than just the number), and then change the extruder number to the preferred extruder, possibly again emitting a signal. Now it just sets the extruder number to the preferred extruder and always emits the signal once (either through setting the extruder number or manually afterwards).

Contributes to issue CURA-6793.

cura/Settings/ExtruderManager.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2018 Ultimaker B.V.
+# Copyright (c) 2019 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
 
 from PyQt5.QtCore import pyqtSignal, pyqtProperty, QObject, QVariant  # For communicating data and events to Qt.
@@ -320,12 +320,8 @@ class ExtruderManager(QObject):
 
         self.resetSelectedObjectExtruders()
 
-    ##  Adds the extruders of the currently active machine.
+    ##  Adds the extruders to the selected machine.
-    def _addCurrentMachineExtruders(self) -> None:
+    def addMachineExtruders(self, global_stack: GlobalStack) -> None:
-        global_stack = self._application.getGlobalContainerStack()
-        if not global_stack:
-            return
-
         extruders_changed = False
         container_registry = ContainerRegistry.getInstance()
         global_stack_id = global_stack.getId()
@@ -351,8 +347,6 @@ class ExtruderManager(QObject):
         self.fixSingleExtrusionMachineExtruderDefinition(global_stack)
         if extruders_changed:
             self.extrudersChanged.emit(global_stack_id)
-            self.setActiveExtruderIndex(0)
-            self.activeExtruderChanged.emit()
 
     # After 3.4, all single-extrusion machines have their own extruder definition files instead of reusing
     # "fdmextruder". We need to check a machine here so its extruder definition is correct according to this.

cura/Settings/MachineManager.py

@@ -219,7 +219,10 @@ class MachineManager(QObject):
             return 0
         return len(general_definition_containers[0].getAllKeys())
 
+    ##  Triggered when the global container stack is changed in CuraApplication.
     def _onGlobalContainerChanged(self) -> None:
+        import traceback
+        traceback.print_stack()
         if self._global_container_stack:
             try:
                 self._global_container_stack.containersChanged.disconnect(self._onContainersChanged)
@@ -298,7 +301,6 @@ class MachineManager(QObject):
         self.blurSettings.emit()  # Ensure no-one has focus.
 
         container_registry = CuraContainerRegistry.getInstance()
-
         containers = container_registry.findContainerStacks(id = stack_id)
         if not containers:
             return
@@ -308,21 +310,25 @@ class MachineManager(QObject):
         # Make sure that the default machine actions for this machine have been added
         self._application.getMachineActionManager().addDefaultMachineActions(global_stack)
 
-        ExtruderManager.getInstance().fixSingleExtrusionMachineExtruderDefinition(global_stack)
+        extruder_manager = ExtruderManager.getInstance()
+        extruder_manager.fixSingleExtrusionMachineExtruderDefinition(global_stack)
         if not global_stack.isValid():
             # Mark global stack as invalid
             ConfigurationErrorMessage.getInstance().addFaultyContainers(global_stack.getId())
             return  # We're done here
 
         self._global_container_stack = global_stack
+        extruder_manager.addMachineExtruders(global_stack)
         self._application.setGlobalContainerStack(global_stack)
-        ExtruderManager.getInstance()._globalContainerStackChanged()
-        self._onGlobalContainerChanged()
 
         # Switch to the first enabled extruder
         self.updateDefaultExtruder()
         default_extruder_position = int(self.defaultExtruderPosition)
-        ExtruderManager.getInstance().setActiveExtruderIndex(default_extruder_position)
+        old_active_extruder_index = extruder_manager.activeExtruderIndex
+        extruder_manager.setActiveExtruderIndex(default_extruder_position)
+        if old_active_extruder_index == default_extruder_position:
+            # This signal might not have been emitted yet (if it didn't change) but we still want the models to update that depend on it because we changed the contents of the containers too.
+            extruder_manager.activeExtruderChanged.emit()
 
         self.__emitChangedSignals()