Setting delegate to MKMapView

Question

I am new to iOS programming. I have created ViewController with MKMapView element, and I wanted to set delegate [mapView setDelegate:self]

First I done it in method initWithNibName:bundle: like:

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {  
        [[self map] setDelegate:self]];
        UITabBarItem *item = [[UITabBarItem alloc] init];
        [item setTitle:@"Map"];
        [self setTabBarItem:item];
    }
    return self;
}

In this case MKMapView did not send me any messages, but when I placed setting delegate message to viewDidLoad method, it worked fine.

Could someone explain me why it was not working when setting delegate message was in initWithNibName:bundle?

Answer 1

Views do not get loaded in initWithNibName, it just initializes your viewcontroller class and load the xib file which contains your view details.

When viewcontroller calls viewDidLoad, you will have all your view objects allocated and initialized.

In your case, when you setDelegate in initWithNibname, you are calling it on a nil value, so nothing get set, but in viewDidLoad mapView is allocated and initialized, so it works fine.

For a deeper insight refer:

http://developer.apple.com/library/ios/#featuredarticles/ViewControllerPGforiPhoneOS/ViewLoadingandUnloading/ViewLoadingandUnloading.html

Beautiful explanation here: What is the process of a UIViewController birth (which method follows which)?

Looking to understand the iOS UIViewController lifecycle

http://thejoeconwayblog.wordpress.com/2012/10/04/view-controller-lifecycle-in-ios-6/

Answer 2

This line is your problem:

[self map]

In initWithNibName the map is not yet initialized and it returns nil.

In viewDidLoad the map is already initialized.