如何计算用户移动时从用户位置到注释的距离 [英] How to calculate distance from user location to annotation when user moves

问题描述

我在 mapView 上有一个用户位置（蓝点）和注释。选择注释时，我将文本设置为 distLabel - 距离点％4.0f m。。如何在用户移动时更新该文本标签？

I have an user location (blue dot) and annotations on mapView. When annotation is selected, I setting text to distLabel - "Distance to point %4.0f m.". How can I update that text label when user moves?

didSelectAnnotationView：

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]];
}

我知道有一个函数 didUpdateToLocation ，但是如何在 didSelectAnnotationView 中使用它？

I know there is a function didUpdateToLocation, but how can I use it with didSelectAnnotationView?

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

推荐答案

地图视图的 selectedAnnotations 您可以在 didUpdateToLocation 方法中使用该属性来判断哪个注释可以获得距离。

The map view has a selectedAnnotations property that you can use in the didUpdateToLocation method to tell which annotation to get the distance from.

（顺便说一句，如果你使用地图视图的 userLocation ，你可能想要使用地图视图的 didUpdateUserLocation 委托方法而不是 didUpdateToLocation 这是 CLLocationManager 委托方法。）

(By the way, if you are using the map view's userLocation, you might want to use the map view's didUpdateUserLocation delegate method instead of didUpdateToLocation which is a CLLocationManager delegate method.)

在委托方法中，您可以检查是否存在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）。

In the delegate method, you can check if there is any currently selected annotation and, if so, show the distance to that annotation (otherwise say "no annotation selected").

您可能想要编写一个可以使用的常用方法从 didSelectAnnotationView 和 didUpdateUserLocation 调用以减少代码重复。

You might want to write a common method that can be called from both didSelectAnnotationView and didUpdateUserLocation to reduce code duplication.

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];
}

这篇关于如何计算用户移动时从用户位置到注释的距离的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！