objective-c : getting locaton

Locations.m

//getting locaton
//1. MyLocations Project Settings

//use tab bar controller
//import CoreLocation.framework

//CurrentLocationViewController.h

#import <CoreLocation/CoreLocation.h>

@interface CurrentLocationViewController : UIViewController <CLLocationManagerDelegate>

@property (nonatomic, weak) IBOutlet UILabel *messageLabel;
@property (nonatomic, weak) IBOutlet UILabel *latitudeLabel;
@property (nonatomic, weak) IBOutlet UILabel *longitudeLabel;
@property (nonatomic, weak) IBOutlet UILabel *addressLabel;
@property (nonatomic, weak) IBOutlet UIButton *tagButton;
@property (nonatomic, weak) IBOutlet UIButton *getButton;

- (IBAction)getLocation:(id)sender;

@end


//CurrentLocationViewController.m

@implementation CurrentLocationViewController
{
  CLLocationManager *_locationManager; //CLLocationManager give you the GPS coordinates
}


- (id)initWithCoder:(NSCoder *)aDecoder
{
  if ((self = [super initWithCoder:aDecoder])) {
    _locationManager = [[CLLocationManager alloc] init];

    // For testing. Uncomment this line to use any location you want,
    // without having to use the Simulator's Location menu.
    //_location = [[CLLocation alloc] initWithLatitude:37.785834 longitude:-122.406417];
  }
  return self;
}

//hooked up to the Get My Location button
- (IBAction)getLocation:(id)sender
{
	_locationManager.delegate = self;
	_locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters; //accuracy of up to ten meters
	[_locationManager startUpdatingLocation]; ////Starts the generation of updates that report the user’s current location
}


#pragma mark - CLLocationManagerDelegate

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


- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
	CLLocation *newLocation = [locations lastObject];
	NSLog(@"didUpdateLocations %@", newLocation);
}


//2. Putting the coordinates on the screen

//FirstViewController.m

@implementation CurrentLocationViewController
{
  CLLocationManager *_locationManager;
  CLLocation *_location; //store the user’s current location in this variable
}


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

  NSLog(@"didUpdateLocations %@", newLocation);

  _location = newLocation;
  [self updateLabels];
}


- (void)updateLabels
{
	if (_location != nil) {

	self.latitudeLabel.text = [NSString stringWithFormat:
	@"%.8f", _location.coordinate.latitude]; //.8 means 8 digits behind the decimal point
	self.longitudeLabel.text = [NSString stringWithFormat:
	@"%.8f", _location.coordinate.longitude];

	self.tagButton.hidden = NO;
	self.messageLabel.text = @"";

	} else {

	// Initially, the screen should say, “Press the Button to Start” and the latitude and longitude labels are empty

	self.latitudeLabel.text = @"";
	self.longitudeLabel.text = @"";
	self.addressLabel.text = @"";
	self.tagButton.hidden = YES;
	self.messageLabel.text = @"Press the Button to Start";

	}
}


- (void)viewDidLoad
{
  [super viewDidLoad];
  [self updateLabels];
}


//3. Handling errors

//CurrentLocationViewController.m

@implementation CurrentLocationViewController
{
  CLLocationManager *_locationManager;
  CLLocation *_location; //store the user’s current location in this variable

  BOOL _updatingLocation; //boolean, If it is NO, then location manager wasn’t currently active and there’s no need to stop it
  NSError *_lastLocationError;
}



#pragma mark - CLLocationManagerDelegate

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

  // The kCLErrorLocationUnknown error means the location manager was unable
  // to obtain a location right now. We will keep trying until we do find a
  // location or receive a more serious error.

  // Some of the Core Location errors:
  // kCLErrorLocationUnknown - The location is currently unknown, but Core Location will keep trying.
  // kCLErrorDenied - The user declined the app to use location services.
  // kCLErrorNetwork - There was a network-related error

  if (error.code == kCLErrorLocationUnknown) {
    return;
  }

  [self stopLocationManager];
  _lastLocationError = error;

  [self updateLabels];
  [self configureGetButton];
}


- (void)stopLocationManager
{
  if (_updatingLocation) {

    // Tell the location manager we no longer want to receive updates.
    [_locationManager stopUpdatingLocation];
    _locationManager.delegate = nil;
    _updatingLocation = NO;
  }
}


- (void)updateLabels
{
  // If we have a location object then we will always show its coordinates,
  // even if we're still fetching a more accurate location at the same time.
  if (_location != nil) {
    self.latitudeLabel.text = [NSString stringWithFormat:@"%.8f", _location.coordinate.latitude];
    self.longitudeLabel.text = [NSString stringWithFormat:@"%.8f", _location.coordinate.longitude];
    self.tagButton.hidden = NO;
    self.messageLabel.text = @"";

  // If we have no location yet, then we're either waiting for the user to
  // press the button to start, still get our first location fix, or we ran
  // into an error situation.
  } else {
    self.latitudeLabel.text = @"";
    self.longitudeLabel.text = @"";
    self.addressLabel.text = @"";
    self.tagButton.hidden = YES;


    //If the location manager gave an error, the label will show an error message
    NSString *statusMessage;
    if (_lastLocationError != nil) {
      if ([_lastLocationError.domain isEqualToString:kCLErrorDomain] && _lastLocationError.code == kCLErrorDenied) {
        statusMessage = @"Location Services Disabled";

      } else {
        statusMessage = @"Error Getting Location";
      }

    } else if (![CLLocationManager locationServicesEnabled]) {
      statusMessage = @"Location Services Disabled";

    } else if (_updatingLocation) {
      statusMessage = @"Searching...";

    } else {
      statusMessage = @"Press the Button to Start";
    }

    self.messageLabel.text = statusMessage;
  }
}


//move getLocation action into its own startLocationManager method
- (void)startLocationManager
{
  if ([CLLocationManager locationServicesEnabled]) { //locationServicesEnabled : Returns a Boolean value indicating whether location services are enabled on the device.

    // Tell the location manager to start fetching the location.
    _locationManager.delegate = self;
    _locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters;
    [_locationManager startUpdatingLocation]; ////Starts the generation of updates that report the user’s current location
    _updatingLocation = YES;
  }
}


//Change the getLocation method to

- (IBAction)getLocation:(id)sender
{
  [self startLocationManager];
  [self updateLabels];
}


//change didUpdateLocations method
//in case there was an error and no location could be obtained
//but walk around for a bit and a valid location comes in
//in that case wipe the old error code

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
	CLLocation *newLocation = [locations lastObject];
	NSLog(@"didUpdateLocations %@", newLocation);
	_lastLocationError = nil; _location = newLocation;
	[self updateLabels];
}


//4. Improving the results

//CurrentLocationViewController.m

//stop getting location updates, when the location is accurate enough

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

  NSLog(@"didUpdateLocations %@", newLocation);

  // If the time at which the new location object was determined is too long
  // ago (5 seconds in this case), then this is a cached result. ignore
  // these cached locations because they may be out of date.
  if ([newLocation.timestamp timeIntervalSinceNow] < -5.0) {
  	//timestamp : The time at which location was determined
    return;
  }

  // Ignore invalid measurements.
  if (newLocation.horizontalAccuracy < 0) {
    return;
  }

  // Only perform the following code if the new location provides a more
  // precise reading than the previous one, or if it's the very first.
  // _location is nil means this is the very first location update
  if (_location == nil || _location.horizontalAccuracy > newLocation.horizontalAccuracy) {

    // Put the new coordinates on the screen.
    _lastLocationError = nil;
    _location = newLocation;
    [self updateLabels];

    // We're done if the new location is accurate enough.
    if (newLocation.horizontalAccuracy <= _locationManager.desiredAccuracy) {
      NSLog(@"*** We're done!");
      [self stopLocationManager];
    }
  }
}


//change the state of button

- (void)configureGetButton
{
  if (_updatingLocation) {
    [self.getButton setTitle:@"Stop" forState:UIControlStateNormal];
  } else {
    [self.getButton setTitle:@"Get My Location" forState:UIControlStateNormal];
  }
}


//call the configureGetButton method

- (void)viewDidLoad {
	[super viewDidLoad];
	[self updateLabels];
	[self configureGetButton];
}

- (IBAction)getLocation:(id)sender {
	[self startLocationManager]; [self updateLabels];
	[self configureGetButton];
}


- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{
	//...
	[self updateLabels];
	[self configureGetButton];
}


- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
	//...
	if (newLocation.horizontalAccuracy <= _locationManager.desiredAccuracy) {
		NSLog(@"*** We're done!");
		[self stopLocationManager];
		[self configureGetButton];
	}
  }
}


- (IBAction)getLocation:(id)sender
{
	if (_updatingLocation) { //_updatingLocation flag to determine what state the app is in
		[self stopLocationManager];

	} else {
		_location = nil;
		_lastLocationError = nil;
		_placemark = nil;
		_lastGeocodingError = nil;

		[self startLocationManager];
	}

	[self updateLabels];
	[self configureGetButton];
}


//5. Reverse Geocoding (using CLGeocoder)
//CLGeocoder object to turn the location data into a human-readable address

//CurrentLocationViewController.m

//add the following instance variables
@implementation CurrentLocationViewController
{
  CLGeocoder *_geocoder;
  CLPlacemark *_placemark; //Placemark data includes information such as the country, state, city, and street address
  BOOL _performingReverseGeocoding;
  NSError *_lastGeocodingError;
}

//create the geocoder object
- (id)initWithCoder:(NSCoder *)aDecoder
{
  if ((self = [super initWithCoder:aDecoder])) {
    //...
    _geocoder = [[CLGeocoder alloc] init];
  }
  return self;
}

//put the geocoder to work

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
  //...
  if (_location == nil || _location.horizontalAccuracy > newLocation.horizontalAccuracy) {
    //...
    if (newLocation.horizontalAccuracy <= _locationManager.desiredAccuracy) {
      //...
    if (!_performingReverseGeocoding) {
      NSLog(@"*** Going to geocode");

      // Unlike the location manager, CLGeocoder does not use a delegate to tell you about the result,
      // but something called a block.

      // Start a new reverse geocoding request and update the screen
      // with the results (a new placemark or error message).
      _performingReverseGeocoding = YES;

      [_geocoder reverseGeocodeLocation:_location completionHandler:^(NSArray *placemarks, NSError *error) {
        NSLog(@"*** Found placemarks: %@, error: %@", placemarks, error);

        _lastGeocodingError = error;
        if (error == nil && [placemarks count] > 0) {
          _placemark = [placemarks lastObject]; //Placemark data includes information such as the country, state, city, and street address
        } else {
          _placemark = nil;
        }

        _performingReverseGeocoding = NO;
        [self updateLabels];
      }];
    }
  }
}


//make the address visible to the user
//Change updateLabels

- (void)updateLabels
{
  // If we have a location object then we will always show its coordinates,
  // even if we're still fetching a more accurate location at the same time.
  if (_location != nil) {
    //...

    // Once we have a location, we try to reverse geocode it and show the
    // results in the address label.
    if (_placemark != nil) {
      self.addressLabel.text = [self stringFromPlacemark:_placemark];
    } else if (_performingReverseGeocoding) {
      self.addressLabel.text = @"Searching for Address...";
    } else if (_lastGeocodingError != nil) {
      self.addressLabel.text = @"Error Finding Address";
    } else {
      self.addressLabel.text = @"No Address Found";
    }

  // If we have no location yet, then we're either waiting for the user to
  // press the button to start, still get our first location fix, or we ran
  // into an error situation.
  } else {
    //...
  }
}


//Add the stringFromPlacemark: 

- (NSString *)stringFromPlacemark:(CLPlacemark *)thePlacemark
{
  return [NSString stringWithFormat:@"%@ %@\n%@ %@ %@",
    thePlacemark.subThoroughfare, thePlacemark.thoroughfare,
    thePlacemark.locality, thePlacemark.administrativeArea,
    thePlacemark.postalCode];

  //subThoroughfare: Additional street-level information for the placemark
  //thoroughfare: The street address associated with the placemark
  //locality: The city associated with the placemark
  //administrativeArea: The state or province associated with the placemark
  //postalCode: The postal code associated with the placemark
}


//in getLocation, clear out the _placemark and _lastGeocodingError variables 
//in order to start with a clean slate

- (IBAction)getLocation:(id)sender
{
  if (_updatingLocation) {
    [self stopLocationManager];
  } else {
    _location = nil;
    _lastLocationError = nil;
    _placemark = nil;
    _lastGeocodingError = nil;

    [self startLocationManager];
  }

  [self updateLabels];
  [self configureGetButton];
}