What is this error with logging out a user with NSUserdefaults? - ios

Question

I do not understand why I get this error:
On logout I call this:
-(void)logoutUser {
NSLog(#"Logging out user");
NSString *appDomain = [[NSBundle mainBundle] bundleIdentifier];
[[NSUserDefaults standardUserDefaults] removePersistentDomainForName:appDomain];
}
And before loading the HomeCollectionViewController I call this to check if NSUserDefaults exist in the Navigation controller wrapping it:
-(void)viewDidAppear:(BOOL)animated {
// Get the stored data before the view loads
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
//if values exist then already logged in else take to login screen
if([[[defaults dictionaryRepresentation] allKeys] containsObject:#"userId"]){
NSLog(#"userId found");
} else {
NSLog(#"userId NOT found");
StarterViewController *hc=[[UIStoryboard storyboardWithName:#"Main" bundle:nil] instantiateViewControllerWithIdentifier:#"Starter"];
[self presentViewController:hc animated:YES completion:nil];
}
}
This is the error:
2014-04-28 10:19:38.431 App[2675:60b] Warning: Attempt to present <HomeCollectionViewController: 0xba9dd10> on <SlidingMenuViewController: 0xba94200> whose view is not in the window hierarchy!
2014-04-28 10:19:38.443 App[2675:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** +[NSJSONSerialization dataWithJSONObject:options:error:]: value parameter is nil'
*** First throw call stack:
(
0 CoreFoundation 0x01dff1e4 __exceptionPreprocess + 180
1 libobjc.A.dylib 0x01b7e8e5 objc_exception_throw + 44
2 CoreFoundation 0x01dfefbb +[NSException raise:format:] + 139
3 Foundation 0x018c4a42 +[NSJSONSerialization dataWithJSONObject:options:error:] + 92
4 Stand 0x00008769 -[HomeCollectionViewController getHomeData] + 297
5 Stand 0x000084a8 -[HomeCollectionViewController viewDidLoad] + 744
6 UIKit 0x0095d33d -[UIViewController loadViewIfRequired] + 696
7 UIKit 0x0095d5d9 -[UIViewController view] + 35
8 UIKit 0x00988509 -[UINavigationController rotatingSnapshotViewForWindow:] + 52
9 UIKit 0x00ccfe3c -[UIClientRotationContext initWithClient:toOrientation:duration:andWindow:] + 420
10 UIKit 0x00884c22 -[UIWindow _setRotatableClient:toOrientation:updateStatusBar:duration:force:isRotating:] + 1495
11 UIKit 0x00884646 -[UIWindow _setRotatableClient:toOrientation:updateStatusBar:duration:force:] + 82
12 UIKit 0x00884518 -[UIWindow _setRotatableViewOrientation:updateStatusBar:duration:force:] + 117
13 UIKit 0x008845a0 -[UIWindow _setRotatableViewOrientation:duration:force:] + 67
14 UIKit 0x0088363a __57-[UIWindow _updateToInterfaceOrientation:duration:force:]_block_invoke + 120
15 UIKit 0x0088359c -[UIWindow _updateToInterfaceOrientation:duration:force:] + 400
16 UIKit 0x008842f3 -[UIWindow setAutorotates:forceUpdateInterfaceOrientation:] + 870
17 UIKit 0x008878e6 -[UIWindow setDelegate:] + 449
18 UIKit 0x00961b77 -[UIViewController _tryBecomeRootViewControllerInWindow:] + 180
19 UIKit 0x0087d474 -[UIWindow addRootViewControllerViewIfPossible] + 591
20 UIKit 0x0087d5ef -[UIWindow _setHidden:forced:] + 312
21 UIKit 0x0087d86b -[UIWindow _orderFrontWithoutMakingKey] + 49
22 UIKit 0x008883c8 -[UIWindow makeKeyAndVisible] + 65
23 UIKit 0x00838bc0 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 2097
24 UIKit 0x0083d667 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 824
25 UIKit 0x00851f92 -[UIApplication handleEvent:withNewEvent:] + 3517
26 UIKit 0x00852555 -[UIApplication sendEvent:] + 85
27 UIKit 0x0083f250 _UIApplicationHandleEvent + 683
28 GraphicsServices 0x03bbff02 _PurpleEventCallback + 776
29 GraphicsServices 0x03bbfa0d PurpleEventCallback + 46
30 CoreFoundation 0x01d7aca5 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 53
31 CoreFoundation 0x01d7a9db __CFRunLoopDoSource1 + 523
32 CoreFoundation 0x01da568c __CFRunLoopRun + 2156
33 CoreFoundation 0x01da49d3 CFRunLoopRunSpecific + 467
34 CoreFoundation 0x01da47eb CFRunLoopRunInMode + 123
35 UIKit 0x0083cd9c -[UIApplication _run] + 840
36 UIKit 0x0083ef9b UIApplicationMain + 1225
37 Stand 0x0000948d main + 141
38 libdyld.dylib 0x0254b701 start + 1
39 ??? 0x00000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

I think you have made an incorrect assumption as to the cause of the problem. Your HomeCollectionViewController is being loaded, so your user defaults isn't the problem. You can see from the stack trace that this view controller is calling a method getHomeData in its viewDidLoad method. It seems that getHomeData is attempting to retrieve some JSON data but the JSON string is nil - as per the exception message.
You need to investigate this method and work out what is going wrong with your JSON.