Application tried to push a nil view controller on target <UINavigationController> mapkit disclosure button

Question

I am trying to add a disclosure button into the callouts of annotations at locations which are parsed in json. I have implemented the disclosure button and everything seems to be working fine until the disclosure button is pushed and I receive this error Application tried to push a nil view controller on target

here is my code for the first viewController

#import "ViewController.h"
#import "DetailViewController.h"
#import "Annotation.h"

#import "City.h"

@interface ViewController ()
@property (nonatomic, strong) IBOutlet DetailViewController *detailViewController;


@end
#define getDatalURL @"http://www.club-hop.com/apptest.php"

@implementation ViewController

@synthesize mapView,jsonArray,citiesArray;


- (void)viewDidLoad
{
[super viewDidLoad];
[self retrieveData];

/* Zoom the map to current location.
[self.mapView setShowsUserLocation:YES];
[self.mapView setUserInteractionEnabled:YES];
[self.mapView setUserTrackingMode:MKUserTrackingModeFollow];*/
City * cityObject;

// load external page into UIWebView
NSMutableArray * locations= [[NSMutableArray alloc]init];
CLLocationCoordinate2D location;
Annotation * myAnn;

for(int u=0; u<citiesArray.count;u++){
cityObject=[citiesArray objectAtIndex:u];

myAnn=[[Annotation alloc]init];
NSNumber *aLat= cityObject.Latitude;
NSNumber *aLon= cityObject.Longitude;

double lat = [aLat doubleValue];
double lon = [aLon doubleValue];

location.latitude= lat;
location.longitude=lon;
myAnn.coordinate = location;
myAnn.title=cityObject.clubName;
myAnn.subtitle=cityObject.cityName;
[locations addObject:myAnn];}

[self.mapView addAnnotations:locations];


}

- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}



//class methods
-(void) retrieveData{
NSURL * url= [NSURL URLWithString:getDatalURL];
NSData * data= [NSData dataWithContentsOfURL:url];
jsonArray= [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];

//setup cities array
citiesArray=[[NSMutableArray alloc]init];

for(int i=0; i<jsonArray.count;i++){
    NSString * cID= [[jsonArray objectAtIndex:i] objectForKey:@"id"];
    NSString * cName= [[jsonArray objectAtIndex:i] objectForKey:@"cityName"];
    NSString * cCountry= [[jsonArray objectAtIndex:i] objectForKey:@"cityCountry"];
    NSString * cLine= [[jsonArray objectAtIndex:i] objectForKey:@"clubLine"];
    NSString * clName= [[jsonArray objectAtIndex:i] objectForKey:@"clubName"];
    NSNumber * cLatitude= [[jsonArray objectAtIndex:i] objectForKey:@"Latitude"];
    NSNumber * cLongitude= [[jsonArray objectAtIndex:i] objectForKey:@"Longitude"];

    [citiesArray addObject:[[City alloc]initWithCityName:cName andCityCountry:cCountry     andClubName:clName andClubLine:cLine andLatitude:cLatitude andLongitude:cLongitude andCityId:cID]];

} 

}

#pragma mark - MKMapViewDelegate

// user tapped the disclosure button in the callout
//
- (void)mapView:(MKMapView *)mapView annotationView:(MKAnnotationView *)view    calloutAccessoryControlTapped:(UIControl *)control
{
id <MKAnnotation> annotation = [view annotation];
if ([annotation isKindOfClass:[Annotation class]])
{
    NSLog(@"clicked annotation");
}

[self.navigationController pushViewController:self.detailViewController animated:YES];

}

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id    <MKAnnotation>)annotation
{

MKPinAnnotationView* pinView = (MKPinAnnotationView *)[mapView    dequeueReusableAnnotationViewWithIdentifier:@"pinView"];

if (!pinView)
{
    pinView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation    reuseIdentifier:@"pinView"] ;
    pinView.pinColor=MKPinAnnotationColorGreen;
    pinView.animatesDrop=YES;
    pinView.canShowCallout=YES;
    UIButton * rightButton= [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
    pinView.rightCalloutAccessoryView=rightButton;
}
else{
    pinView.annotation=annotation;
}
return pinView;

    }


@end

Any incite into why I am receiving this error would be greatly appreciated.

Answer 1

you haven't allocated or init'd self.detailViewController. You created a property called detailViewController and then never did anything with it.

try this:

- (void)viewDidLoad
{
    self.detailViewController = [[DetailViewController alloc] init];
}