Use Current Location Service in Map

Posted in code with : ios

Jul 21, 2015

Location Service Authorization

1. Set info.plist

For iOS SDK 8.0 and later, we need to set NSLocationWhenInUseUsageDescription and ‘NSLocationAlwaysUsageDescription’ in info.plist file. A sample case is:

1 <key>NSLocationWhenInUseUsageDescription</key>
2 <string>Do you allow the app to use your location?</string>
3 <key>NSLocationAlwaysUsageDescription</key>
4 <string>Are you willing to allow the app to use your location?</string>

The string will appear in the popup dialog. You can leave it as empty, and only the system message will appear in the popup.

2. Ask the User for Location Service Authorization

We ask for the authorization by an instance of CLLocationManager.

import CoreLocation/CoreLocation.h class, and define a location manager locationManager in the map view controller.
use the following code for asking authorization from user:

 1 if ([CLLocationManager locationServicesEnabled] ) { // check if the location service is enabled for the device
 2     if (self.locationManager == nil ) {
 3         self.locationManager = [[CLLocationManager alloc] init];
 4         self.locationManager.desiredAccuracy = kCLLocationAccuracyBest;
 5         self.locationManager.distanceFilter = kCLDistanceFilterNone;
 6     }
 7     // Check for iOS 8. Without this guard the code will crash with "unknown selector" on iOS 7.
 8     if([self.locationManager respondsToSelector:@selector(requestAlwaysAuthorization)]){
 9         CLAuthorizationStatus locationAuthorizationStatus = [CLLocationManager authorizationStatus];
10         if (locationAuthorizationStatus == kCLAuthorizationStatusNotDetermined && ([self.locationManager respondsToSelector:@selector(requestAlwaysAuthorization)] || [self.locationManager respondsToSelector:@selector(requestWhenInUseAuthorization)])) {
11             // choose one request according to your business.
12             if([[NSBundle mainBundle] objectForInfoDictionaryKey:@"NSLocationAlwaysUsageDescription"]){
13                 [self.locationManager requestAlwaysAuthorization];
14             } else if([[NSBundle mainBundle] objectForInfoDictionaryKey:@"NSLocationWhenInUseUsageDescription"]) {
15                 [self.locationManager  requestWhenInUseAuthorization];
16             } else {
17                 NSLog(@"Info.plist does not contain NSLocationAlwaysUsageDescription or NSLocationWhenInUseUsageDescription");
18             }
19         }
20     }
21 }

Get Location

For iOS SDK 8.0 and later, we have two ways to get user current location:

set showsUserLocation to YES for map view.
send method startUpdatingLocation to CLLocationManager instance.

1. showsUserLocation

For this way, after we set showsUserLocation to YES,

We can get the location in mapView:didUpdateUserLocation:.

 1 - (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
 2 {
 3     // Center the map the first time we get a real location change.
 4     static dispatch_once_t centerMapFirstTime;
 5     
 6     if ((userLocation.coordinate.latitude != 0.0) && (userLocation.coordinate.longitude != 0.0)) {
 7         dispatch_once(&centerMapFirstTime, ^{
 8             [self.mapView setCenterCoordinate:userLocation.coordinate animated:YES];
 9         });
10     }
11     
12 }

We can set the current location annotation view in mapView:viewForAnnotation:. If nil is returned, a default blue circle with white boundary is use. The circle has breathing effect. For this purpose, we need to identify the annotation (which is an id type) type: if it is a MKUserLocation type, return a current location annotation view or nil. Question: How to define whether an id type object is a MKUserLocation type object?

Before implementing the above two methods, we should set the map view’s delegate comfirm with MapViewDelegate protoco.

2. Send message `startUpdateingLocation` to `CLLocationManager` Instaance

For this way, after we send the method,

We can get the location in locationManager:didUpdateLocations:. The newest location is the lastObject of locations.

 1 - (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
 2 {
 3     self.currentLocation = [locations lastObject];
 4     CLLocationCoordinate2D currentCoordinate = self.currentLocation.coordinate;
 5     
 6     if (self.currentLocationAnnotation) {
 7         [self.mapView removeAnnotation:self.currentLocationAnnotation];
 8     }
 9     self.currentLocationAnnotation = [[CurrentLocationAnnotation alloc] initWithCoordinate:currentCoordinate];
10     [self.mapView addAnnotation:self.currentLocationAnnotation];
11 }

When you add the current location annotation to map view, you can set the current location annotation view in mapView:viewForAnnotation: method. If nil is returned, a red pin will be use as the annotation view. Question: How can we use the default blue circle as the annotation view, just as we set showsUserLocation to YES?
You can also get erroe message when app fails to get the location in locationManager:didFailWithError: method.

1 - (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
2 {
3     NSLog(@"didFailWithError: %@", error);
4     UIAlertView *errorAlert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"Failed to Get Your Location" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
5     [errorAlert show];
6 }

Before implementing the above methods, set the CLLocationManager’s delegate confirm with CLLocationManagerDelegate protoco.

References

reference: