Question

BACKGROUND:

I have a custom UIViewController class where I populate a MKMapView with custom annotations. When the user selects the annotation, details about that annotation are displayed, and a button is also present for the user to select and bring up another UIViewController with details about that point on the map.

The Code:

I initialize the new view controller by creating the class with a UserID (Note: - (id) initWithUserID:(NSInteger) userID; is declared in the header file of the SecondViewController:

@interface SecondViewController ()

@property (nonatomic) NSInteger userID;

@end



@implementation RainFallDetailedViewController

@synthesize userID = _userID;


- (id) initWithUserID:(NSInteger) userID{

_userID = userID;
NSLOG(@"UserID: %i",self.userID); //correctly displays user id

return self;
}

- (void) viewWillAppear{
NSLOG(@"UserID: %i",self.userID); //userid is now 0

Creating the view controller is done when the button is pressed, and then immediately performs the segue to the second view controller:

- (void)mapView:(MKMapView *)mapView 
annotationView:(MKAnnotationView *)view calloutAccessoryControlTapped:(UIControl *)control {

if ([(UIButton*)control buttonType] == UIButtonTypeInfoLight){ //I'm looking for recognition of the correct button being pressed here.
    //SecondViewController is the second view controller with the detailed information about the map point.  
    //DataPoint is a custom class that contains the details regarding the map point.
    SecondViewController *detailedMapController = [[SecondViewController alloc] initWithUserID:((DataPoint *)view.annotation).userID]; 

    NSLOG(@"UserID: %i", ((DataPoint *)view.annotation).userID); //correctly displays userID

    [self performSegueWithIdentifier:@"PinDetail" sender:detailedMapController];


} 
}

PROBLEM:

Using NSLOG I’m able to confirm that the value is being passed correctly when creating the class. However, when I go to use the property userID later on in the code (viewWillAppear), it’s not longer there for me to use. I’m assuming that there’s a memory issue that I’m not taking care of but I can’t seem to figure it out. How do I ensure that the values/object I pass into a class upon creation stay there?

Side Note: I originally tried, passing a PinData object, but ran into the same issue, so I know it’s not a NSInteger problem. I’ve also followed noa’s suggestion and used prepareForSegue however, I get the same problem presented above

Answer 1

The segue is responsible for instantiating the controller. Don’t instantiate another one – it’ll just be discarded, which is why the property values don’t seem to stick.

To set up the view controller, override -prepareForSegue: instead, in the parent view controller:

- (void) prepareForSegue:(UIStoryboardSegue *) segue sender:(id) sender {
    if ([segue.identifier isEqualToString:@"PinDetail"]) {
        SecondViewController *vc = segue.destinationViewController;
        vc.userID = self.userID;
    }
}

Replace the last block of code above with this:

self.userID = ((RainFallDataPoint *)view.annotation).userID;
[self performSegueWithIdentifier:@"PinDetail" sender:self];