为什么这个swift代码错了？

问题描述：

出于某种原因，因为我更新我碰到下面的错误与MultiPeer connectivty工作时，我似乎无法弄清楚：为什么这个swift代码错了？

“类型MessageServiceManager不符合协议MCSession”

一切都过去完美，但现在出于某种原因，一切都破裂了，我不知道为什么。这是它让所有调动起来代码：

extension MessageServiceManager : MCSessionDelegate { 
    func session(_ session: MCSession, peer peerID: MCPeerID, didChange state: MCSessionState) { 
    NSLog("%@", "peer \(peerID) didChangeState: \(state.stringValue())") 
    self.delegate?.connectedDevicesChanged(self, connectedDevices: session.connectedPeers.map({$0.displayName})) 
    } 

    func session(_ session: MCSession, didReceive data: Data, fromPeer peerID: MCPeerID) { 
    NSLog("%@", "didReceiveData: \(data)") 
    let str = NSString(data: data, encoding: String.Encoding.utf8.rawValue) as! String 
    self.delegate?.messageChanged(self, messageString: str) 
    } 

    func session(_ session: MCSession, didReceive stream: InputStream, withName streamName: String, fromPeer peerID: MCPeerID) { 
    NSLog("%@", "didReceiveStream") 
    } 

    func session(_ session: MCSession, didFinishReceivingResourceWithName resourceName: String, fromPeer peerID: MCPeerID, at localURL: URL??, withError error: Error?) { 
    NSLog("%@", "didFinishReceivingResourceWithName") 
} 

    func session(_ session: MCSession, didStartReceivingResourceWithName resourceName: String, fromPeer peerID: MCPeerID, with progress: Progress) { 
    NSLog("%@", "didStartReceivingResourceWithName") 
    } 
}

好吧，错误消息告诉你所有你需要知道的：你的类不符合'MCSessionDelegate' - 要么使用自动完成，要么手动检查'MessageServiceManager'从协议中错过了什么 –

没有错过那个问题 – SemAllush

答

当提的是：

类型MessageServiceManager不符合协议MCSession

这意味着，你是不您班上的所有必需方法均符合MCSessionDelegate。

要解决这个问题，您可以按指令并点击MCSessionDelegate，然后选择“Jump to Definition”。应该引导你：

// Delegate methods for MCSession. 
public protocol MCSessionDelegate : NSObjectProtocol { 


    // Remote peer changed state. 
    @available(iOS 7.0, *) 
    public func session(_ session: MCSession, peer peerID: MCPeerID, didChange state: MCSessionState) 


    // Received data from remote peer. 
    @available(iOS 7.0, *) 
    public func session(_ session: MCSession, didReceive data: Data, fromPeer peerID: MCPeerID) 


    // Received a byte stream from remote peer. 
    @available(iOS 7.0, *) 
    public func session(_ session: MCSession, didReceive stream: InputStream, withName streamName: String, fromPeer peerID: MCPeerID) 


    // Start receiving a resource from remote peer. 
    @available(iOS 7.0, *) 
    public func session(_ session: MCSession, didStartReceivingResourceWithName resourceName: String, fromPeer peerID: MCPeerID, with progress: Progress) 


    // Finished receiving a resource from remote peer and saved the content 
    // in a temporary location - the app is responsible for moving the file 
    // to a permanent location within its sandbox. 
    @available(iOS 7.0, *) 
    public func session(_ session: MCSession, didFinishReceivingResourceWithName resourceName: String, fromPeer peerID: MCPeerID, at localURL: URL?, withError error: Error?) 


    // Made first contact with peer and have identity information about the 
    // remote peer (certificate may be nil). 
    @available(iOS 7.0, *) 
    optional public func session(_ session: MCSession, didReceiveCertificate certificate: [Any]?, fromPeer peerID: MCPeerID, certificateHandler: @escaping (Bool) -> Swift.Void) 
}

这是协议的声明。

现在您可以识别您必须实现的方法（所有非可选方法）或方法签名是否匹配;你会注意到：

session(_:didFinishReceivingResourceWithName:fromPeer:at:withError:)

是不，因为它应该是让来抱怨的编译器的原因，实现明明所有你需要做的就是实现它为：

func session(_ session: MCSession, didFinishReceivingResourceWithName resourceName: String, fromPeer peerID: MCPeerID, at localURL: URL?, withError error: Error?) { 
    // your logic goes here... 
}

答

你有一个双重问号'??'在其中一种方法中。

所以更改此设置：

func session(_ session: MCSession, didFinishReceivingResourceWithName resourceName: String, fromPeer peerID: MCPeerID, at localURL: URL??, withError error: Error?) { 
    NSLog("%@", "didFinishReceivingResourceWithName") 
}

这样：

func session(_ session: MCSession, didFinishReceivingResourceWithName resourceName: String, fromPeer peerID: MCPeerID, at localURL: URL?, withError error: Error?) { 
    NSLog("%@", "didFinishReceivingResourceWithName") 
}

注意去除的 '？' URL之后的字符。

为什么这个swift代码错了？

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