如何计算用户移动时从用户位置到注释的距离

Question

我有一个用户位置(蓝点)和注释mapView.选择注释时,我将文本设置为distLabel- "距离点%4.0f m.".用户移动时如何更新该文本标签？

didSelectAnnotationView:

- (void)mapView:(MKMapView *)mapView didSelectAnnotationView:(MKAnnotationView *)view
{

    CLLocation *pinLocation = 
      [[CLLocation alloc] initWithLatitude:
                        [(MyAnnotation*)[view annotation] coordinate].latitude 
                                 longitude:
                        [(MyAnnotation*)[view annotation] coordinate].longitude];
    CLLocation *userLocation = 
      [[CLLocation alloc] initWithLatitude:
                          self.mapView.userLocation.coordinate.latitude             
                                 longitude:
                                 self.mapView.userLocation.coordinate.longitude];        
    CLLocationDistance distance = [pinLocation distanceFromLocation:userLocation];

    [distLabel setText: [NSString stringWithFormat:@"Distance to point %4.0f m.",    
                                                     distance]];
}

我知道有一个功能didUpdateToLocation,但我怎么能用didSelectAnnotationView呢？

- (void)locationManager:(CLLocationManager *)manager
    didUpdateToLocation:(CLLocation *)newLocation
           fromLocation:(CLLocation *)oldLocation
{
  //Did update to location
}

Answer 1

地图视图有一个selectedAnnotations属性,您可以在didUpdateToLocation方法中使用该属性来指示哪个注释可以获得距离.

(顺便说一下,如果你正在使用的地图视图的userLocation,则可能需要使用地图视图的didUpdateUserLocation委托方法,而不是didUpdateToLocation这是一个CLLocationManager委托方法.)

在委托方法中,您可以检查是否有任何当前选定的注释,如果是,则显示该注释的距离(否则说"未选择注释").

您可能希望编写一个可以从两者中调用的常用方法,didSelectAnnotationView并didUpdateUserLocation减少代码重复.

例如:

-(void)updateDistanceToAnnotation:(id<MKAnnotation>)annotation
{
    if (annotation == nil) 
    {
        distLabel.text = @"No annotation selected";
        return;
    }

    if (mapView.userLocation.location == nil) 
    {
        distLabel.text = @"User location is unknown";
        return;
    }

    CLLocation *pinLocation = [[CLLocation alloc] 
        initWithLatitude:annotation.coordinate.latitude
               longitude:annotation.coordinate.longitude];

    CLLocation *userLocation = [[CLLocation alloc] 
        initWithLatitude:mapView.userLocation.coordinate.latitude 
               longitude:mapView.userLocation.coordinate.longitude];

    CLLocationDistance distance = [pinLocation distanceFromLocation:userLocation];

    [distLabel setText: [NSString stringWithFormat:@"Distance to point %4.0f m.", distance]];
}

-(void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
{
    if (mapView.selectedAnnotations.count == 0)
        //no annotation is currently selected
        [self updateDistanceToAnnotation:nil];
    else
        //first object in array is currently selected annotation
        [self updateDistanceToAnnotation:[mapView.selectedAnnotations objectAtIndex:0]];
}

- (void)mapView:(MKMapView *)mapView didSelectAnnotationView:(MKAnnotationView *)view
{    
    [self updateDistanceToAnnotation:view.annotation];
}