initialization and allocation without arc? - ios

Question

Sorry its a basic question, I want to know why my code doesn't need alloc/init for mapView. Does it happen automatically on retain ? I am not using ARC and on alloc/init of my MKMapView* mapView it does not result in error but the map view doesn't show the location information and also doesn't appear as hybrid type....but on removing the alloc/init statement fro viewDidLoad it works all fine !! why?
#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>
#import <MapKit/MapKit.h>
#interface MDViewController : UIViewController<CLLocationManagerDelegate, MKMapViewDelegate>
#property (retain, nonatomic) IBOutlet MKMapView* mapView;
#end
-----
#import "MDViewController.h"
#interface MDViewController ()
{
CLLocationManager* lmanager;
}
#end
#implementation MDViewController
#synthesize mapView;
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
lmanager= [[CLLocationManager alloc]init];
lmanager.delegate=self;
lmanager.desiredAccuracy=kCLLocationAccuracyBest;
lmanager.distanceFilter=kCLDistanceFilterNone;
[lmanager startUpdatingLocation];
//mapView = [[MKMapView alloc]init];//without allocating here it works
mapView.delegate=self;
mapView.mapType=MKMapTypeHybrid;
}
-(void) locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
//update map
MKCoordinateSpan span;
span.latitudeDelta= .001;
span.longitudeDelta=.001;
MKCoordinateRegion region;
region.center= newLocation.coordinate;
region.span=span;
[mapView setRegion:region animated:YES];
[mapView setShowsUserLocation:YES];
}

Answer 1

You don't need to alloc init your mapview because it is done for you by the Xib. When loading the interface xib, the frameworks see you have a frozen mapview and alloc init it automagically, then assign that mapview to the one in your viewcontroller code.
If in your code you alloc init, you break the link between the two.
One way to make it work is to have no mapview in your IB xib and alloc init it, setDelegate, set frame and finally add its view as a subview of the main view.
I try to stay concise. I hope it us clear to you. And ARC has no relation whatsoever with all that.