Listen to extruder-stack changes for extruder_prime_pos*

CURA-1944

cura/BuildVolume.py

@@ -78,6 +78,10 @@ class BuildVolume(SceneNode):
         Application.getInstance().globalContainerStackChanged.connect(self._onGlobalContainerStackChanged)
         self._onGlobalContainerStackChanged()
 
+        self._active_extruder_stack = None
+        ExtruderManager.getInstance().activeExtruderChanged.connect(self._onActiveExtruderStackChanged)
+        self._onActiveExtruderStackChanged()
+
     def setWidth(self, width):
         if width: self._width = width
 
@@ -254,6 +258,13 @@ class BuildVolume(SceneNode):
 
             self.rebuild()
 
+    def _onActiveExtruderStackChanged(self):
+        if self._active_extruder_stack:
+            self._active_extruder_stack.propertyChanged.disconnect(self._onSettingPropertyChanged)
+        self._active_extruder_stack = ExtruderManager.getInstance().getActiveExtruderStack()
+        if self._active_extruder_stack:
+            self._active_extruder_stack.propertyChanged.connect(self._onSettingPropertyChanged)
+
     def _onSettingPropertyChanged(self, setting_key, property_name):
         if property_name != "value":
             return