using Delegates in models to pass information between them

Question

I want to make a HTTP request, and part of the request contains a lat and lng.

To get these I have a Location modal. One of it's delegate lets me know when it have a location ready. When that happens, I call my custom delegate which gets implemented in my Foursquare model.

I start everything in my MainViewController by creating an instance of the Location model and call startUpdatingLocation method. The implementation looks something like this:

Location model:

- (void)startLocationManager
{
    _locationManager = [[CLLocationManager alloc] init];
    _locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters;
    _locationManager.delegate = self;

    [_locationManager startUpdatingLocation];
}

- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{
    NSLog(@"Error:%@", error.userInfo);
}

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
    if (locations) {
        _location = [locations lastObject];
        [self.delegate location:self didFinishFindingLocation:_location];
    }

}

Foursquare model:

- (void)location:(Location *)loc didFinishFindingLocation:(CLLocation *)location
{
    NSString *search = [NSString stringWithFormat:@"https://api.foursquare.com/v2/venues/search?ll=%f,%f&radius=2000&categoryId=4d4b7105d754a06374d81259&client_id=%@&client_secret=%@&v=%@", location.coordinate.latitude, location.coordinate.longitude, kFourdquareAPIKey, fFoursquareSecret, [Foursquare getCurrentDate]];

    NSURL *url = [NSURL URLWithString:search];
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config];

    NSURLSessionDataTask *task = [session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
        NSDictionary *dataDictionary = (NSDictionary *)[NSJSONSerialization JSONObjectWithData:data options:0 error:&error];
        self.dataResponse = dataDictionary[@"response"][@"venues"];
        NSLog(@"%@", self.dataResponse);
    }];

    [task resume];
}

Lastly, I do this in my MainViewController:

Location *location = [[Location alloc] init];
[location startLocationManager];

Nothing is logged to the console, and the simulator doesn't ask me for permission to get locations. Nothing.

1) Is it wrong to use delegates like this? 2) Is there a better way?

Given that 1's answer is no, what's wrong with my code?

Answer 1 · 2014-02-11T23:23:50Z

February 11, 2014 11:23pm

Amit gave me the correct answer a couple of days ago in a related post. I'll paste his answer:

"You need to make location a property of your view controller instead of a local variable in the viewDidLoad. Otherwise it is created and deallocated within that method. You need it to live through the lifecycle of your view controller."

As soon as I did that it solved my problems.. ;)

Answer 2 · 2014-02-09T09:53:04Z

February 9, 2014 9:53am

Did you tell your class that you are using the CLLocationDelegate protocol in your header? This goes behind the class name and superclass definition with <> brackets.

Otherwise use breakpoints to see if your application actually calls your methods. When the program stops at those breakpoints you can log your objects to the console egg. using "po locations" to see if your objects are not nil.

Answer 3 · 2014-02-11T23:10:27Z

February 11, 2014 11:10pm

Hey, did you try adding the CLLocationManagerDelegate? You have to just add it in your interface after the class declaration. Should look something like this I guess

@interface MainViewController : UIViewController <CLLocationManagerDelegate>

Welcome to the Treehouse Community

Looking to learn something new?

Thomas Nilsen

Thomas Nilsen

using Delegates in models to pass information between them

3 Answers

Thomas Nilsen

Thomas Nilsen

Sabine Geithner

Sabine Geithner

Thomas Nilsen

Thomas Nilsen

Thomas Nilsen

Thomas Nilsen

Sabine Geithner

Sabine Geithner