Swift:使用完成处理程序通知另一个视图控制器

I have 2 ViewControllers in my app. One of them named vcA is using a method (here viewDidLoad) to talk to my networking layer (a class in my app). After finishing the networking job (which will be inferred by a completion handler) I want to notify class vcB to call a method to get some data which is provided by networking layer. Please take a look at below sudo code :I have 2 ViewControllers in my app. One of them