我正在尝试thistutorial代码有问题:classMPCManager:NSObject,MCSessionDelegate,MCNearbyServiceBrowserDelegate,MCNearbyServiceAdvertiserDelegate{我遇到了一个错误:Type'MPCManager'doesnotcomformtoprotocol'MCSessionDelegate'Type'MPCManager'doesnotcomformtoprotocol'MCNearbyServiceBrowserDelegate'Type'MPCManager'doesnotco