Blocks location helper for finding location on an iphone

LocationHelper.m

//
//  LocationHelper.m
//
//  Created by Chris Hulbert on 24/04/12.
//  Modified by Richard Das 15/10/12.
//

#import "LocationHelper.h"

@interface LocationHelper()
@property(copy) LocationBlock locationBlock;
@property(strong) CLLocationManager* locMan;
@end

@implementation LocationHelper
@synthesize bestEffortAtLocation, locationBlock, locMan;

+ (void)getLocation:(LocationBlock)block {
    if ([CLLocationManager locationServicesEnabled]) {
        
        // We have to instantiate something so we can use it as a delegate. Boo hiss. Blocks rule!
        LocationHelper* lh = [[LocationHelper alloc] init];
        lh.locationBlock = block;
        
        // Kick off the location finder
        lh.locMan = [[CLLocationManager alloc] init];
        lh.locMan.desiredAccuracy = kCLLocationAccuracyKilometer; // Get the roughest accuracy (eg use cell towers not gps)
        lh.locMan.delegate = lh;
        lh.locMan.purpose = locationHelperPurpose;
        [lh.locMan startUpdatingLocation];
        
        // This serves two purposes: keep the instance retained by the runloop, and timeout if things don't work
        [lh performSelector:@selector(timeout) withObject:nil afterDelay:10.0];
        
    } else {
        block(nil); // Not enabled
    }
}

// This is used to keep the instance retained by the runloop, and to call the block just in case the location manager didn't
- (void)timeout
{
    if (self.locationBlock) {
        self.locationBlock(nil);
        self.locationBlock=nil;
    }
    [self.locMan stopUpdatingLocation];
    self.locMan = nil;
}


#pragma mark - Delegate stuff


- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
    
    if (self.locationBlock) {
        
        // test the age of the location measurement to determine if the measurement is cached
        // in most cases you will not want to rely on cached measurements
        NSTimeInterval locationAge = -[newLocation.timestamp timeIntervalSinceNow];
        if (locationAge > 5.0) return;

        // test that the horizontal accuracy does not indicate an invalid measurement
        if (newLocation.horizontalAccuracy < 0) return;

        // test the measurement to see if it is more accurate than the previous measurement
        
        NSLog(@"LocHelper New Location accuracy: %f x %f", newLocation.horizontalAccuracy, newLocation.verticalAccuracy );

        if ( self.bestEffortAtLocation == nil || self.bestEffortAtLocation.horizontalAccuracy > newLocation.horizontalAccuracy )
        {
            // store the location as the "best effort"
            self.bestEffortAtLocation = newLocation;

            if (newLocation.horizontalAccuracy <= self.locMan.desiredAccuracy)
            {
                // pass it on to the block
                self.locationBlock(newLocation);
                self.locationBlock=nil;

                // we have a measurement that meets our requirements, so we can stop updating the location
                [self.locMan stopUpdatingLocation];
                self.locMan = nil;
                
                // we can also cancel our previous performSelector:withObject:afterDelay: - it's no longer necessary
                [NSObject cancelPreviousPerformRequestsWithTarget:manager selector:@selector(timeout) object:nil];
            }
        }
    }
}

// If it fails,
- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{
    NSLog(@"Location manager failed: %@", error);
    
    if (self.locationBlock) {
        self.locationBlock(nil);
        self.locationBlock=nil;
    }    
    [self.locMan stopUpdatingLocation];
    self.locMan = nil;
}

@end