assembly: use new API canAddToSceneGraph()

assembly.py

@@ -90,7 +90,8 @@ class ViewProviderAsmBase(object):
         vobj.Proxy = self
         self.attach(vobj)
 
-    _addToSceneGraph = False
+    def canAddToSceneGraph(self):
+        return False
 
     def attach(self,vobj):
         if hasattr(self,'ViewObject'):
@@ -98,8 +99,6 @@ class ViewProviderAsmBase(object):
         self.ViewObject = vobj
         vobj.signalChangeIcon()
         vobj.setPropertyStatus('Visibility','Hidden')
-        if not self._addToSceneGraph:
-            vobj.Document.ActiveView.getSceneGraph().removeChild(vobj.RootNode)
 
     def __getstate__(self):
         return None
@@ -2358,7 +2357,6 @@ class Assembly(AsmGroup):
 
 class ViewProviderAssembly(ViewProviderAsmGroup):
     _iconName = 'Assembly_Assembly_Frozen_Tree.svg'
-    _addToSceneGraph = True
 
     def __init__(self,vobj):
         self._movingPart = None
@@ -2369,6 +2367,9 @@ class ViewProviderAssembly(ViewProviderAsmGroup):
         if not hasattr(vobj,'ShowParts'):
             vobj.addProperty("App::PropertyBool","ShowParts"," Link")
 
+    def canAddToSceneGraph(self):
+        return True
+
     def onDelete(self,vobj,_subs):
         assembly = vobj.Object.Proxy
         for o in assembly.getPartGroup().Group: