Event set on delegate - iphone

Question

I am trying to understand some concept here regarding delegate and callbacks. Basically I am trying to make an http-request, which is based on zipcode. So prior making http-request, I call a location-manager and grab a zipcode, however, in such duration, I have to wait async to complete that task, and get the feedback. The concern here is, the delegate I have set from location-manager, have no link with http-request class. So, I am trying to understand how can I pass the information back from delegate to http-request. I was looking into blocks, but again is there anyway in blocks that you can wait for a response of a delegate? or it can be also set as a BOOL property in async task, when completed can trigger the request. I haven't tried blocks much except for GCD, so still trying to get my heads around this.
I welcome any suggestions here.

Answer 1

Here is a sketch - (ignoring error conditions and location data caching issues). This could all go in the viewController. There is one block for obtaining the zip code, but the rest of it can be done through delegates if you prefer.
//initialise locationManager once (eg in viewDidLoad)
- (void) initialiseLocationManager
{
CLLocationManager* locationManager = [[CLLocationManager alloc] init];
[locationManager setDelegate:self];
[locationManager setDesiredAccuracy:kCLLocationAccuracyKilometer];
[locationManager setDistanceFilter:500];
self.locationManager = locationManager;
}
//[self startLocating] whenever you want to initiate another http-request
- (void) startLocating
{
[self.locationManager startUpdatingLocation];
}
//locationManager delegate method
//this will get triggered after [self startLocating]
//when a location result is returned
- (void)locationManager:(CLLocationManager *)manager
didUpdateLocations:(NSArray *)locations
{
CLLocation* location = [locations lastObject];
CLGeocoder* geocoder = [[CLGeocoder alloc] init];
[geocoder reverseGeocodeLocation:location
completionHandler:^(NSArray *placemarks, NSError *error){
CLPlacemark* placemark = [placemarks objectAtIndex:0];
NSString* zip = [placemark postalCode];
/*
implement your http-request code here using the zip string
there are various ways to do this
but two ways your result will arrive...
1 - as a delegate callback
so you would implement the relevant delegate method
(in this same viewController) to use the result
2 - as a completion block
so your result-using method would be that block
*/
}];
[self.locationManager stopUpdatingLocation];
}

Answer 2

In delegation you would have one controller (could be your view controller) that conforms to both protocols, the location manager's protocol and the protocol defined by the http rquest controller.
the view controller creates both objects and assigns itself as the delegate for both.
It tells the location manger to grab the zip code. Once the manager is done, it sends an appropriate delegate method on the delegate [self.delegate didFindZipCode:code onLocationManager: self]. As the delegate is the view controller, it implements this method
-(void)didFindZipCode:(NSString *)code onLocationManager:(MyLocationManager *)manager
{
[self.httpRequestController sendZipCode:code];
}
and the request controller will inform the view controller in a similar way as soon as the desired data is available.
actually blocks would be dealing with this in a similar way — just that no delegate is set, that should be called, but that a code is passed around, that will be called as soon as something happened.

Answer 3

There is a wonderful library available, called AFNetworking, which is very easy to implement.
It uses blocks, which greatly simply communication of data between classes (does away with delegates).