Swift Notification error: unrecognized selector sent to instance

Question

For some reason this has just started happening. The only thing I did today was add the launch images.

I am getting this error:

2017-09-14 03:51:59.110379 GameTest[2671:668473] -[NSConcreteNotification length]: unrecognized selector sent to instance 0x1702503b0
2017-09-14 03:51:59.134158 GameTest[2671:668473] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSConcreteNotification length]: unrecognized selector sent to instance 0x1702503b0'
*** First throw call stack:
(0x1895581c0 0x187f9055c 0x18955f278 0x18955c278 0x18945659c 0x1010327ac 0x100ff8738 0x10145dcf8 0x1000711d0 0x1894f222c 0x1894f1930 0x1894f16ac 0x189560b9c 0x189433bf4 0x189f396bc 0x1000756f8 0x10004bc3c 0x10175525c 0x10175521c 0x10175a284 0x189505f2c 0x189503b18 0x189432048 0x18aeb3198 0x18f395bd0 0x18f390908 0x100078d68 0x1884145b8)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)

In my app delegate I have this code from

reachability.whenReachable = { reachability in
    // this is called on a background thread, but UI updates must
    // be on the main thread, like this:
    DispatchQueue.main.async {
        if reachability.isReachableViaWiFi {
            NotificationCenter.default.post(name: NSNotification.Name(rawValue: "hasInternet"), object: nil)
        } else {
            NotificationCenter.default.post(name: NSNotification.Name(rawValue: "hasInternet"), object: nil)
        }
    }
}
reachability.whenUnreachable = { reachability in
    // this is called on a background thread, but UI updates must
    // be on the main thread, like this:
    DispatchQueue.main.async {
        NotificationCenter.default.post(name: NSNotification.Name(rawValue: "noInternet"), object: nil)
    }
}

The error seems to be this line:

NotificationCenter.default.post(name: NSNotification.Name(rawValue: "noInternet"), object: nil)

Can someone help me fix this? The other questions do not seem to be related to notifications and I am not finding them useful.

Can you post the code of the things that observe the noInternet notification? My inclination is that the selector you pass to that method may be incorrect. — Fred Faust
I'm having this same issue (crash on calling post). Seems crazy to me since this is so basic and I've used NotificationCenter so many times before. — Brian Sachetta

pwc pwc · Accepted Answer · 2018-06-18T20:53:49

Check the parameter type of the selector you are passing to NotificationCenter.addObserver(_:selector:name:object). The selector must have one and only one argument, an instance of Notification.

I suspect you are calling (either directly or indirectly) length on the object being passed in to your selector. That is not defined on the Notification type, hence the exception.

Swift Notification error: unrecognized selector sent to instance

2 Answers