objective-c MKMapView center on user location

Question

I'm trying to zoom into the user location as the center reference for the screen. I have this code:

MainViewController.h

#import <UIKit/UIKit.h>
#import "FlipsideViewController.h"
#import <MapKit/MapKit.h>
#import <CoreLocation/CoreLocation.h>

IBOutlet MKMapView *mapView;

@interface MainViewController : UIViewController <FlipsideViewControllerDelegate, MKMapViewDelegate> {
   MKMapView *mapView;
}
@property (nonatomic, retain) IBOutlet MKMapView *mapView;

MainViewController.m

@implementation MainViewController
@synthesize mapView;

 - (void)viewDidLoad {
    [super viewDidLoad];
    mapView = [[MKMapView alloc]
           initWithFrame:self.view.bounds
           ];
    mapView.showsUserLocation = YES;
    mapView.mapType = MKMapTypeHybrid;
    mapView.delegate = self;
    [self.view addSubview:mapView];
}

- (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation {
    MKCoordinateRegion region;
    MKCoordinateSpan span;
    span.latitudeDelta = 0.005;
    span.longitudeDelta = 0.005;
    CLLocationCoordinate2D location;
    location.latitude = userLocation.coordinate.latitude;
    location.longitude = userLocation.coordinate.longitude;
    region.span = span;
    region.center = location;
    [mapView setRegion:region animated:YES];
 }

Now I'm only getting a build warning on the last line [mapView setRegion:region animated:YES] stating: 'local declaration of 'mapView' hides instance variable'

Fortnightly

Answer 1

When you do mapView.showsUserLocation = YES;, you ask it to retrieve the user location. This doesn't happen instantly. As it takes time, the map view notifies its delegate that a user location is available via the delegate method mapView:didUpdateUserLocation. So you should adopt the MKMapViewDelegate protocol and implement that method. You should move all your zooming-in code to this method.

Setting the delegate

- (void)viewDidLoad {
    [super viewDidLoad];
    mapView = [[MKMapView alloc]
           initWithFrame:CGRectMake(0, 
                                    0,
                                    self.view.bounds.size.width, 
                                    self.view.bounds.size.height)
           ];
    mapView.showsUserLocation = YES;
    mapView.mapType = MKMapTypeHybrid;
    mapView.delegate = self;
    [self.view addSubview:mapView];
}

Updated delegate method

- (void)mapView:(MKMapView *)aMapView didUpdateUserLocation:(MKUserLocation *)aUserLocation {
    MKCoordinateRegion region;
    MKCoordinateSpan span;
    span.latitudeDelta = 0.005;
    span.longitudeDelta = 0.005;
    CLLocationCoordinate2D location;
    location.latitude = aUserLocation.coordinate.latitude;
    location.longitude = aUserLocation.coordinate.longitude;
    region.span = span;
    region.center = location;
    [aMapView setRegion:region animated:YES];
}

Godliman

I am extremely new to objective-c so bear with me...how I do call the didUpdateUserLocation method from within the didViewLoad method? – Fortnightly

You don't. You adopt the protocol as @Srikar pointed out and as you seem to have done and then assign yourself as its delegate like mapView.delegate = self;. The map view will notify you on its own when it has the necessary information. – Godliman

@Deepak @Srikar - please view my original post to see what is happening now after I updated things.... – Fortnightly

@Fortnightly Have you set the delegate? – Godliman

@Deepak - you should how to set the delegate but where do I do that? I tried putting it in the viewDidLoad and in the DidUpdateUserLocation methods and I got a build error "MainViewController does not implement the MKMapViewDelegate protocol". – Fortnightly

@Deepak - also, thats all I have in the console to show you - there is nothing else – Fortnightly

@Deepak - like I said (check my OP for an update of the delete part also) I get an error "MainViewController does not implement the MKMapViewDelegate protocol" on this line. – Fortnightly

Have you done this @interface MainViewController : UIViewController <FlipsideViewControllerDelegate, MKMapViewDelegate> like Srikar said? – Godliman

And one final thing the delegate method is - (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation and not the method shorthand mapView:didUpdateUserLocation: – Godliman

@Deepak - my bad - I didn't put MKMapViewDelegate inside the @interface declaration - after doing this the zoom executes successfully. One last problem though is after implementing your last two suggestions I am now getting build warnings for location.longitute, location.latitude, and [mapView setRegion...] stating: 'location declaration of mapView hides instance variable' Do you know what this could be from? – Fortnightly

yeah you have a property called userLocation and one of the arguments of the delegate method is also userLocation. Change the latter to aUserLocation. It should work. – Godliman

I took the mapView off the front of mapView.userLocation.coordinate.latitude, etc. changing it to userLocation.coordinate.latitude and it fixed those two lines but I'm still receiving the error for [mapView setRegion:region animated:YES]. – Fortnightly

Which error are you getting? And can you update the question with your latest code? – Godliman

Local variables are masking the instance variables. Adjusted the delegate method and edited it into my answer. – Godliman

Answer 2

In your interface you forgot to inherit MapViewDelegate -

#import <MapKit/MapKit.h>

@interface MainViewController : UIViewController <FlipsideViewControllerDelegate, MKMapViewDelegate> 
{
   MKMapView *mapView;
}
@property (nonatomic, retain) IBOutlet MKMapView *mapView;

Rest seems fine.

Bovill

I added your @property line and still am receiving the same problem error – Fortnightly

I changed some stuff in my OP please check it again – Fortnightly