Notify WatchKit app of an update without the watch app requesting it

Question

I\'m aware of the capabilities of WKInterfaceController openParentApplication and handleWatchKitExtensionRequest methods for the watch app to open

Answer 1

With WatchOS 2, you can sendMessage method like that;

Parent App

import WatchConnectivity then;

Add this to didFinishLaunchingWithOptions method in AppDelegate;

if #available(iOS 9.0, *) {
    if WCSession.isSupported() {
        let session = WCSession.defaultSession()
        session.delegate = self
        session.activateSession()

        if !session.paired {
            print("Apple Watch is not paired")
        }
        if !session.watchAppInstalled {
            print("WatchKit app is not installed")
        }
    } else {
        print("WatchConnectivity is not supported on this device")
    }
} else {
     // Fallback on earlier versions
}

Then in your notification function;

func colorChange(notification: NSNotification) {
     if #available(iOS 9.0, *) {
        if WCSession.defaultSession().reachable {
           let requestValues = ["color" : UIColor.redColor()]
           let session = WCSession.defaultSession()

           session.sendMessage(requestValues, replyHandler: { _ in
                    }, errorHandler: { error in
                        print("Error with sending message: \(error)")
                })
            } else {
                print("WCSession is not reachable to send data Watch App from iOS")
            }
     } else {
         print("Not available for iOS 9.0")
     }
 }

Watch App

Do not forget to import WatchConnectivity and add WCSessionDelegate to your InterfaceController

override func awakeWithContext(context: AnyObject?) {
    super.awakeWithContext(context)

    // Create a session, set delegate and activate it
    if (WCSession.isSupported()) {
        let session = WCSession.defaultSession()
        session.delegate = self
        session.activateSession()
    } else {
        print("Watch is not supported!")
    }
}

func session(session: WCSession, didReceiveMessage message: [String : AnyObject], replyHandler: ([String : AnyObject]) -> Void) { 
    if let deviceColor = message["color"] as? UIColor {
        // do whatever you want with color
    }
}

To do this, your Watch App need to work on foreground.