向Apple Watch发送消息时，应用程序崩溃

我在iOS应用程序中有一个UIButton动作（ sendMessageToWatch ），在Apple Watch中有一个标签（ messageLabel ） . 我想要做的是点击iPhone中的按钮，然后在Apple Watch的标签中看到它 .

出于某种原因，当我点击按钮时，应用程序崩溃而不输出任何错误 .

我错过了什么？

这是代码 .

iOS ViewController

import UIKit
import WatchConnectivity

class ViewController: UIViewController, WCSessionDelegate {

    var session: WCSession!

    override func viewDidLoad() {
        super.viewDidLoad()
        if WCSession.isSupported() {
            let session = WCSession.default()
            session.delegate = self
            session.activate()
        }
    }

    func session(_ session: WCSession, activationDidCompleteWith activationState: WCSessionActivationState, error: Error?) {}
    func sessionDidDeactivate(_ session: WCSession) { }
    func sessionDidBecomeInactive(_ session: WCSession) { }

    @IBAction func sendMessageToWatch(_ sender: Any) {
        //Send Message to Watch
        let messageToSend:Dictionary = ["messageFromPhone":"Hello Watch."]

        session.sendMessage(messageToSend, replyHandler: { replyMessage in
            // some replay
        }, errorHandler: {error in
            // catch any errors here
        })
    }

}

Watch InterfaceController

import WatchKit
import Foundation
import WatchConnectivity

class InterfaceController: WKInterfaceController, WCSessionDelegate {

    var session: WCSession!
    @IBOutlet var messageLabel: WKInterfaceLabel!

    func session(_ session: WCSession, didReceiveMessage message: [String : Any], replyHandler: @escaping ([String : Any]) -> Void) {
        //handle received message
        let value = message["messageFromPhone"] as? String
        DispatchQueue.main.async {
            self.messageLabel.setText(value)
        }
    }

    override func awake(withContext context: Any?) {
        super.awake(withContext: context)
    }

    override func willActivate() {
        // This method is called when watch view controller is about to be visible to user
        super.willActivate()

        if (WCSession.isSupported()) {
            session = WCSession.default()
            session.delegate = self
            session.activate()
        }
    }

    override func didDeactivate() {
        // This method is called when watch view controller is no longer visible
        super.didDeactivate()
    }

    func session(_ session: WCSession, activationDidCompleteWith activationState: WCSessionActivationState, error: Error?) {}
}