Swift app crashes with `unrecognized selector sent to instance` on CLLocationManager

Question

Similar to many, many other questions on StackOverflow, I get a unrecognized selector sent to instance fault, when running my app. What makes my case different (I think) is that it is written in Swift and that the common reason is not the reason here.

In this question the solution is to set the "Custom Class" in the Identity Inspector for that view to the responding class. I checked this and this is the case (note that I did rename the class at some point, but it now is definitely set to "ViewController").

I include the stack trace below as well as the code for ViewController.swift. You can also find all of the code here. I managed to avoid this problem by starting fresh, which enabled me to solve my earlier question. This new trial can be found in this branch. But, I want to know what is wrong and solve this.

Some thought

One question that I couldn't answer successfully is whether CLLocationManagerDelegate needs some required methods? But because I got it to work in the other branch, I suspect it's not necessary.

2014-07-03 21:50:26.056 RowingTracker2[11416:60b] -[CLLocationManager requestWhenInUseAuthorization]: unrecognized selector sent to instance 0xa10c4a0
2014-07-03 21:50:26.059 RowingTracker2[11416:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[CLLocationManager     requestWhenInUseAuthorization]: unrecognized selector sent to instance 0xa10c4a0'
*** First throw call stack:
(
    0   CoreFoundation                      0x008831e4 __exceptionPreprocess + 180
1   libobjc.A.dylib                     0x01e2a8e5 objc_exception_throw + 44
2   CoreFoundation                      0x00920243 -[NSObject(NSObject) doesNotRecognizeSelector:] + 275
3   CoreFoundation                      0x0087350b ___forwarding___ + 1019
4   CoreFoundation                      0x008730ee _CF_forwarding_prep_0 + 14
5   RowingTracker2                      0x00003352 _TFC14RowingTracker214ViewController11viewDidLoadfS0_FT_T_ + 738
6   RowingTracker2                      0x000033a2 _TToFC14RowingTracker214ViewController11viewDidLoadfS0_FT_T_ + 34
7   UIKit                               0x0102f33d -[UIViewController loadViewIfRequired] + 696
8   UIKit                               0x0102f5d9 -[UIViewController view] + 35
9   UIKit                               0x00f4f267 -[UIWindow addRootViewControllerViewIfPossible] + 66
10  UIKit                               0x00f4f5ef -[UIWindow _setHidden:forced:] + 312
11  UIKit                               0x00f4f86b -[UIWindow _orderFrontWithoutMakingKey] + 49
12  UIKit                               0x00f5a3c8 -[UIWindow makeKeyAndVisible] + 65
13  UIKit                               0x00f0abc0 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 2097
14  UIKit                               0x00f0f667 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 824
15  UIKit                               0x00f23f92 -[UIApplication handleEvent:withNewEvent:] + 3517
16  UIKit                               0x00f24555 -[UIApplication sendEvent:] + 85
17  UIKit                               0x00f11250 _UIApplicationHandleEvent + 683
18  GraphicsServices                    0x031fff02 _PurpleEventCallback + 776
19  GraphicsServices                    0x031ffa0d PurpleEventCallback + 46
20  CoreFoundation                      0x007feca5 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 53
21  CoreFoundation                      0x007fe9db __CFRunLoopDoSource1 + 523
22  CoreFoundation                      0x0082968c __CFRunLoopRun + 2156
23  CoreFoundation                      0x008289d3 CFRunLoopRunSpecific + 467
24  CoreFoundation                      0x008287eb CFRunLoopRunInMode + 123
25  UIKit                               0x00f0ed9c -[UIApplication _run] + 840
26  UIKit                               0x00f10f9b UIApplicationMain + 1225
27  RowingTracker2                      0x00008021 top_level_code + 97
28  RowingTracker2                      0x0000805b main + 43
29  libdyld.dylib                       0x024ff701 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

ViewController.swift

import UIKit
import MapKit
import CoreLocation

class ViewController: UIViewController, MKMapViewDelegate, CLLocationManagerDelegate {
    @IBOutlet var mapview: MKMapView = nil
    var locationmgr : CLLocationManager!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        locationmgr = CLLocationManager()
        locationmgr.delegate = self
        locationmgr.requestWhenInUseAuthorization() ///< Offending line.
//        mapview.showsUserLocation = true
    }


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

Answer 1

As requestWhenInUseAuthorization method is only available on iOS 8 (according to Apple Documentation) you have to wrap it:

Swift code:

if (locationmgr.respondsToSelector(Selector("requestWhenInUseAuthorization"))) {
  locationmgr.requestWhenInUseAuthorization()
}

And the same for Objective-C:

if ([locationmgr respondsToSelector:@selector(requestWhenInUseAuthorization)]) {
    [locationmgr requestWhenInUseAuthorization];
}

Answer 2

This code won't run on iOS 7 and below - according the docs, requestWhenInUseAuthorization is only available on iOS 8:

Availability:

Available in iOS 8.0 and later.