UIA notification event: add the handler if IUIAutomation5 is in use. Re

nvaccess#7984.

If IUIAutomation5 is in use, add notificaiton event handler, otherwise COM error is thrown.
Also, instead of relying solely on Python MRO to retrieve UIA interface, save the string somewhere for reference purposes and for future use.

source/_UIAHandler.py

@@ -211,11 +211,14 @@ def MTAThreadFunc(self):
 			except (COMError,WindowsError,NameError):
 				self.clientObject=CoCreateInstance(CUIAutomation._reg_clsid_,interface=IUIAutomation,clsctx=CLSCTX_INPROC_SERVER)
 			if isUIA8:
+				# #8009: use appropriate interface based on highest supported interface, and if not, fall back to IUIAutomation2 (Windows 8).
 				try:
-					self.clientObject=self.clientObject.QueryInterface(IUIAutomation5)
+					self.clientObject=self.clientObject.QueryInterface(_getIUIAInterface10())
 				except COMError:
-					self.clientObject=self.clientObject.QueryInterface(IUIAutomation4)
-			log.info("UIAutomation: %s"%self.clientObject.__class__.__mro__[1].__name__)
+					self.clientObject=self.clientObject.QueryInterface(IUIAutomation2)
+			# Have this handy because we want to add things corresponding to the interface version.
+			IUIAVersion = self.clientObject.__class__.__mro__[1].__name__
+			log.info("UIAutomation: %s"%IUIAVersion)
 			self.windowTreeWalker=self.clientObject.createTreeWalker(self.clientObject.CreateNotCondition(self.clientObject.CreatePropertyCondition(UIA_NativeWindowHandlePropertyId,0)))
 			self.windowCacheRequest=self.clientObject.CreateCacheRequest()
 			self.windowCacheRequest.AddProperty(UIA_NativeWindowHandlePropertyId)
@@ -235,7 +238,9 @@ def MTAThreadFunc(self):
 			self.clientObject.AddPropertyChangedEventHandler(self.rootElement,TreeScope_Subtree,self.baseCacheRequest,self,UIAPropertyIdsToNVDAEventNames.keys())
 			for x in UIAEventIdsToNVDAEventNames.iterkeys():  
 				self.clientObject.addAutomationEventHandler(x,self.rootElement,TreeScope_Subtree,self.baseCacheRequest,self)
-			self.clientObject.AddNotificationEventHandler(self.rootElement,TreeScope_Subtree,self.baseCacheRequest,self)
+			# #8009: add support for notification event (IUIAutomation5, part of Windows 10 build 16299 and later).
+			if IUIAVersion >= "IUIAutomation5":
+				self.clientObject.AddNotificationEventHandler(self.rootElement,TreeScope_Subtree,self.baseCacheRequest,self)
 		except Exception as e:
 			self.MTAThreadInitException=e
 		finally: