Question

I have seen al most all the other posts about this, but I can’t seem to get it. I am new to iOS and objective-C, and I am following the Big Nerd Ranch Guides for both Objective-C and iOS. One of the challenges I found on their site is to make a simple CoreLocation app, and I am trying to separate out the code into classes so I can reuse it later if I would like to.

I want to get the button in my ViewController.m file to call locationManager in MyLocation.m file, which is the MyLocation class. I have looked into NSNotificaiton, but I could not get that to work correctly either.

I cannot for the life of me figure out what I am missing or doing wrong. I apologize for the simplicity of the question, and I am trying to learn as many basics as possible.

Below are my files:

ViewController.h:

#import <UIKit/UIKit.h>
#import "MyLocation.h"

@interface ViewController : UIViewController
- (IBAction)GetLocation:(id)sender;
@property (weak, nonatomic) IBOutlet UILabel *LocationOutput;

@end

ViewController.m:

#import "ViewController.h"
#import "MyLocation.h"

@interface ViewController ()

@end

@implementation ViewController
@synthesize LocationOutput;

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{
    [self setLocationOutput:nil];
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

- (IBAction)GetLocation:(id)sender {

    //WHAT GOES HERE?
}
@end

MyLocation.h:

#import <Foundation/Foundation.h>
#import <CoreLocation/CoreLocation.h>

@class MyLocation;

@protocol MyLocationDelegate <NSObject>;

@end

@interface MyLocation : NSObject <CLLocationManagerDelegate>
@property (nonatomic, strong) CLLocationManager *locationManager;

@end

MyLocation.m:

#import "MyLocation.h"

@implementation MyLocation
@synthesize locationManager = _locationManager;

-(void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
    NSLog(@"Latitude is: %f", newLocation.coordinate.latitude);
}

@end

I know I am not outputting anything yet to the label, but I am doing an NSLog.

Thank you for any help. I really appreciate it.

Answer 1

In order to send messages to an object, you need to have a reference to it. In the two classes you are posting, you have the same issue: you don’t have a reference to them, so you won’t be able to send them messages.

In ViewController, you need to somehow get a reference to a MyLocation object. For example, if you changed your code to:

- (IBAction)GetLocation:(id)sender {
    MyLocation *myLocation = [[[MyLocation alloc] init] autorelease];
    [myLocation someMethod];
}

This will, on each call to the action, instantiate a new MyLocation object, and send it the someMethod message. In your case, this is a little bit more complex. Your MyLocation class needs to have an instance of CLLocationManager instantiated. Probably, you need an instance variable for it and do something like this:

@interface MyLocation {
    CLLocationManager *_locationMananger;
}
@end

@implementation MyLocation

- (id)init {
   self = [super init];
   if (self) {
       _locationManager = [[CLLocationManager alloc] init];
       _locationManager.delegate = self;
   }
   return self;
}

- (void)dealloc {
   [_locationManager release];

   [super dealloc];
}

@end

Then, the CLLocationManager instance you created on MyLocation will call its delegate method when the location changes. What you should do in that method, is store that location in some instance variable of MyLocation, so you can access it at a later point.

Finally, I would change the ViewController to create the MyLocation instance only once, at its initialization, or view load:

@interface ViewController {
    MyLocation *_myLocation;
}
@end

@implementation ViewController

- (id)initWithNibName:(NSString *)nibName bundle:(NSBundle *)bundle {
    self = [super initWithNibName:nibName bundle:bundle];
    if (self) {
        _myLocation = [[MyLocation alloc] init];
    }
    return self;
}

- (void)dealloc {
   [_myLocation release];
   [super dealloc];
}

- (IBAction)GetLocation:(id)sender {
   // Grab the location from _myLocation using a property or method defined
}

@end

Hope you get the idea and this can get you started.