No longer spam the GUI with hasUserSettingsUpdates

The QML profiler showed me that it was causing a *lot* of issues
when switching between extruders. More than 10% of the time in QML
was spent on just updating ine property in the workspace summary dialog.
There were other properties that were also being updated without there being a point.

Contributes to #8250

cura/Settings/MachineManager.py

@@ -63,6 +63,7 @@ class MachineManager(QObject):
         self._current_root_material_id = {}  # type: Dict[str, str]
 
         self._default_extruder_position = "0"  # to be updated when extruders are switched on and off
+        self._num_user_settings = 0
 
         self._instance_container_timer = QTimer()  # type: QTimer
         self._instance_container_timer.setInterval(250)
@@ -126,6 +127,8 @@ class MachineManager(QObject):
         self.activeQualityGroupChanged.connect(self.activeQualityDisplayNameChanged)
         self.activeQualityChangesGroupChanged.connect(self.activeQualityDisplayNameChanged)
 
+        self.activeStackValueChanged.connect(self._reCalculateNumUserSettings)
+
     activeQualityDisplayNameChanged = pyqtSignal()
 
     activeQualityGroupChanged = pyqtSignal()
@@ -151,6 +154,22 @@ class MachineManager(QObject):
     printerConnectedStatusChanged = pyqtSignal() # Emitted every time the active machine change or the outputdevices change
 
     rootMaterialChanged = pyqtSignal()
+    numUserSettingsChanged = pyqtSignal()
+
+    def _reCalculateNumUserSettings(self):
+        if not self._global_container_stack:
+            if self._num_user_settings != 0:
+                self.numUserSettingsChanged.emit()
+                self._num_user_settings = 0
+            return
+        num_user_settings = self._global_container_stack.getTop().getNumInstances()
+        stacks = self._global_container_stack.extruderList
+        for stack in stacks:
+            num_user_settings += stack.getTop().getNumInstances()
+
+        if self._num_user_settings != num_user_settings:
+            self._num_user_settings = num_user_settings
+            self.numUserSettingsChanged.emit()
 
     def setInitialActiveMachine(self) -> None:
         active_machine_id = self._application.getPreferences().getValue("cura/active_machine")
@@ -415,31 +434,13 @@ class MachineManager(QObject):
         Logger.log("d", "Checking %s stacks for errors took %.2f s" % (count, time.time() - time_start))
         return False
 
-    @pyqtProperty(bool, notify = activeStackValueChanged)
+    @pyqtProperty(bool, notify = numUserSettingsChanged)
     def hasUserSettings(self) -> bool:
-        """Check if the global_container has instances in the user container"""
+        return self._num_user_settings != 0
 
-        if not self._global_container_stack:
+    @pyqtProperty(int, notify = numUserSettingsChanged)
-            return False
-
-        if self._global_container_stack.getTop().getNumInstances() != 0:
-            return True
-
-        for stack in self._global_container_stack.extruderList:
-            if stack.getTop().getNumInstances() != 0:
-                return True
-
-        return False
-
-    @pyqtProperty(int, notify = activeStackValueChanged)
     def numUserSettings(self) -> int:
-        if not self._global_container_stack:
+        return self._num_user_settings
-            return 0
-        num_user_settings = self._global_container_stack.getTop().getNumInstances()
-        stacks = self._global_container_stack.extruderList
-        for stack in stacks:
-            num_user_settings += stack.getTop().getNumInstances()
-        return num_user_settings
 
     @pyqtSlot(str)
     def clearUserSettingAllCurrentStacks(self, key: str) -> None: