当一个位置更改用户位置而第二个位置更改用户位置时，如何计算位置之间的距离？

Question

I have IBAction :

-(IBAction)pressStart{

locationManager.delegate = self;
[locationManager startUpdatingLocation];

}

In

    - (void)viewDidLoad
    {
        [super viewDidLoad];
        duration.text = @"00:00:00";
        speedLabel.text = @"00";
        locationManager = [[CLLocationManager alloc]init];
        locationManager.distanceFilter = kCLDistanceFilterNone;
        locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation;
    }

And this method:

   - (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations{

    CLLocation *firstLocation = [locations objectAtIndex:0];
    location = [locations lastObject];
    CLLocationDistance meters = [location distanceFromLocation:firstLocation];

    NSLog(@"meters= %f", meters);

And I don't know why the firstLocation is changing. Maybe there is a way to capture firstLocation? This should be the location of the device when the button Start is pressed.

Answer 1

firstLocation in your code is not the first location since location updates started; it is the first location to be returned to you since the previous callback to the locationManager:didUpdateLocations: method (the location services may collect multiple locations before calling back to your delegate method in certain circumstances -- the most recent location is always going to be the last object in the locations array).

If you need to store the first location since location updates started, you should create a property such as

@property (nonatomic, strong) CLLocation *startingLocation;

Then in the locationManager:didUpdateLocations: method, add the code:

if (!self.startingLocation) {
    self.startingLocation = [locations objectAtIndex:0];
}

That will store the starting location into the property after the first callback. (You can set the property to nil if you want to reset it.)

Don't forget that the very first location you receive many not be very accurate, as it takes time for location services to get a fix on the device's position if they were not recently enabled.