Application tried to push a nil view controller on target iOS7 - ios

Question

I have a "problem" with the following code. The error message is: Application tried to push a nil view controller on target UINavigationController:0x10b82bbf0 when clicking on annotation #4's callout.
How can I make it open an alertview without getting this error?
//Callout button action
- (void)mapView:(MKMapView *)mapView annotationView:(MKAnnotationView *)view
calloutAccessoryControlTapped:(UIControl *)control{
if ([view.annotation isKindOfClass:[Annotation class]])
{
Annotation *myAnn = (Annotation *)view.annotation;
id vcToPush = nil;
if ([[myAnn title] isEqualToString:#"1. Annotation one"]){
vcToPush = [[FirstViewController alloc]init];
}
if ([[myAnn title] isEqualToString:#"2. Annotation two"]){
vcToPush = [[SecondViewController alloc]init];
}
if ([[myAnn title] isEqualToString:#"3. Annotation three"]){
vcToPush = [[ThirdViewController alloc]init];
}
if ([[myAnn title] isEqualToString:#"4. Annotation four"]){
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:#"Fourth annotation" message:#"Message" delegate:nil cancelButtonTitle:#"OK"
otherButtonTitles:nil];
[alertView show];
}
[self.navigationController pushViewController:vcToPush animated:YES];
}
}
//Custom callout
- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)myAnn {
//Current location blue dot
if ([myAnn isKindOfClass:[MKUserLocation class]])
{
((MKUserLocation *)myAnn).title = #"My position";
return nil;
}//
MKPinAnnotationView *pinView = (MKPinAnnotationView *)[mapView dequeueReusableAnnotationViewWithIdentifier:#"pinView"];
if (!pinView) {
pinView = [[MKPinAnnotationView alloc] initWithAnnotation:myAnn reuseIdentifier:#"pinView"];
pinView.pinColor = MKPinAnnotationColorRed;
pinView.canShowCallout = YES;
pinView.rightCalloutAccessoryView = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
}
else
{
pinView.annotation = myAnn;
}
return pinView;
}
Thank you!

Answer 1

In the if block
if ([[myAnn title] isEqualToString:#"4. Annotation four"]){
vcToPush is not initialize. Therefore is has the value it had before the method got called (nil in this case).
I assume you only want to show an alert in case of #4. In this case, add a return in the if block:
if ([[myAnn title] isEqualToString:#"4. Annotation four"]){
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:#"Fourth annotation" message:#"Message" delegate:nil cancelButtonTitle:#"OK" otherButtonTitles:nil];
[alertView show];
return;
}