Core Data error message - ios

Question

I created a Core Data Entity named: "Athlete".
Here is the error that I am getting:
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name 'Athlete''
This is the line at where it breaks:
Athlete *detail = [NSEntityDescription insertNewObjectForEntityForName:#"Athlete" inManagedObjectContext:context];
delegate.h
#property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
#property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
#property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;
delegate.m
-(void)createData{
NSManagedObjectContext *context = [self managedObjectContext];
Athlete *detail = [NSEntityDescription insertNewObjectForEntityForName:#"Athlete" inManagedObjectContext:context];
detail.first = #"Joe";
detail.last = #"Pastrami";
detail.phone = #"[phone]";
NSError *error;
if(![context save:&error]){
NSLog(#"Error :(");
}
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Athlete" inManagedObjectContext:context];
[request setEntity:entity];
NSArray *arr = [context executeFetchRequest:request error:&error];
for (Athlete *ath in arr){
NSLog(#"Name %#", ath.first);
}
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
[self createData];
}

Answer 1

The error says it all: your managedObjectContext is nil.

Answer 2

Have you correctly passed your managedObjectContext object from AppDelegate to your UIViewController? If not, 2 ways to do this:
From AppDelegate (example app with UINavigationController at root):
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
NSManagedObjectContext *context = [self managedObjectContext];
UINavigationController *navigationController = (UINavigationController *)self.window.rootViewController.navigationController;
YourViewController *yourViewController = (SearchViewController *)navigationController.topViewController;
yourViewController.managedObjectContext = self.managedObjectContext;
...
}
From YourViewController:
#import AppDelegate.h
...
#synthesize managedObjectContext;
- (void)viewDidLoad
AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication]delegate];
managedObjectContext = [appDelegate managedObjectContext];
...
}