Plotting a users route taken on a map using MKPolyline

Question

I'm quite new to Objective-c.

In my app, I'm trying to plot the users taken route onto a map.

Here is what I have so far that just gets the users current location:

#import "StartCycleViewController.h"
#import "CrumbPath.h"


@interface StartCycleViewController ()

@property (nonatomic, strong) CLLocationManager *locationManager;

@property (nonatomic, strong) IBOutlet MKMapView *map;

@property (nonatomic, strong) UIView *containerView;





@end

@implementation StartCycleViewController

@synthesize cycleLocation = _cycleLocation;
@synthesize currentCycleLocation = _currentCycleLocation;






 - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
 {
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
    // Custom initialization
    }
    return self;
 }

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self startCycleLocation];

    _containerView = [[UIView alloc] initWithFrame:self.view.bounds];
    [self.view addSubview:self.containerView];

    [self.containerView addSubview:self.map];
    // Do any additional setup after loading the view.
}


- (void)dealloc
{
    self.locationManager.delegate = nil;
}


- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


#pragma mark - startCycleLocation

- (void)startCycleLocation{

    if (!_cycleLocation){
        _cycleLocation = [[CLLocationManager alloc]init];
        _cycleLocation.desiredAccuracy = kCLLocationAccuracyBestForNavigation;
        _cycleLocation.distanceFilter = 10;
        _cycleLocation.delegate = self;

    }
    [_cycleLocation startUpdatingLocation];

}

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation     *)newLocation fromLocation:(CLLocation *)oldLocation {

    NSLog(@"didUpdateToLocation: %@", newLocation);
    CLLocation *currentLocation = newLocation;

    if (currentLocation != nil) {
    self.longitudeLabel.text = [NSString stringWithFormat:@"%.8f",    currentLocation.coordinate.longitude];
    self.latitudeLabel.text = [NSString stringWithFormat:@"%.8f",    currentLocation.coordinate.latitude];

    }
}



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

    if ( [error code] != kCLErrorLocationUnknown ){
        [self stopLocationManager];
    }
}

- (void) stopLocationManager {
    [self.cycleLocation stopUpdatingLocation];
}



@end

I've had a look around online and gather that I should use MKPolylineand give it coordinates. But I'm just not sure how I would store the locations and then send them use MKPolyline to plot the points, continuously while the app is running.

Answer 1

You should just create a NSMutableArray to hold your locations that you instantiate in viewDidLoad. So have didUpdateToLocation (or, if supporting iOS 6 and higher, you should use didUpdateToLocations) simply add a location to an array, then build a MKPolyline from that array, add that MKPolyline to the map, and then remove the old MKPolyline. Or you could add all of the line segments as individual MKPolyline objects, but the idea is the same, create a model to hold you locations (e.g. a NSMutableArray) and then add the appropriate MKPolyline object(s) to the map view.

For example, you could do something like:

#pragma mark - CLLocationManagerDelegate

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
    CLLocation *location = [locations lastObject];

    if (location.horizontalAccuracy < 0)
        return;

    [self.locations addObject:location];
    NSUInteger count = [self.locations count];

    if (count > 1) {
        CLLocationCoordinate2D coordinates[count];
        for (NSInteger i = 0; i < count; i++) {
            coordinates[i] = [(CLLocation *)self.locations[i] coordinate];
        }

        MKPolyline *oldPolyline = self.polyline;
        self.polyline = [MKPolyline polylineWithCoordinates:coordinates count:count];
        [self.mapView addOverlay:self.polyline];
        if (oldPolyline)
            [self.mapView removeOverlay:oldPolyline];
    }
}

And remember to specify how the map is to draw the MKPolyline. So set your view controller to be a the delegate of your MKMapView, and you can then do something like the following:

#pragma mark - MKMapViewDelegate

- (MKOverlayRenderer *)mapView:(MKMapView *)mapView rendererForOverlay:(id<MKOverlay>)overlay
{
    if ([overlay isKindOfClass:[MKPolyline class]])
    {
        MKPolylineRenderer *renderer = [[MKPolylineRenderer alloc] initWithPolyline:overlay];

        renderer.strokeColor = [[UIColor blueColor] colorWithAlphaComponent:0.7];
        renderer.lineWidth   = 3;

        return renderer;
    }

    return nil;
}

// for iOS versions prior to 7; see `rendererForOverlay` for iOS7 and later

- (MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id <MKOverlay>)overlay
{
    if ([overlay isKindOfClass:[MKPolyline class]])
    {
        MKPolylineView *overlayView = [[MKPolylineView alloc] initWithPolyline:overlay];

        overlayView.strokeColor     = [[UIColor blueColor] colorWithAlphaComponent:0.7];
        overlayView.lineWidth       = 3;

        return overlayView;
    }

    return nil;
}