ios - 从用户位置 ios 查找最近的注释？

Question

我有一组注释。我正在计算每个注释与用户位置之间的距离。我想知道的是，我怎样才能找到距离这些距离最近的 3 个注释？

这是我计算从用户位置到注释的距离的方法。

  CLLocation *userLocation = self.mapView.userLocation.location;

  for (Annotation *obj in annotations) {

       CLLocation *loc = [[CLLocation alloc] initWithLatitude:obj.coordinate.latitude longitude:obj.coordinate.longitude];
      //  CLLocation *userLocation = [[CLLocation alloc] initWithLatitude:self.mapView.userLocation.coordinate.latitude longitude:self.mapView.userLocation.coordinate.longitude];
        CLLocationDistance dist = [loc distanceFromLocation:userLocation];
        int distance = dist;
        NSLog(@"Distance from Annotations - %i", distance);


    }

Answer 1

userLocation 是静态的，所以不要在循环中每次都重新创建它。您还可以通过以下方式直接获取位置:

CLLocation *userLocation = self.mapView.userLocation.location;

然后，您可以执行类似的操作，将您的距离数字和注释存储到字典中，将距离作为键，将注释作为值。构建字典后，对 allKeys 数组进行排序，然后您可以获得与前 3 个键关联的注释。

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假设您在运行此命令时始终至少有一个注释:

CLLocation *userLocation = self.mapView.userLocation.location;
NSMutableDictionary *distances = [NSMutableDictionary dictionary];

for (Annotation *obj in annotations) {
    CLLocation *loc = [[CLLocation alloc] initWithLatitude:obj.coordinate.latitude longitude:obj.coordinate.longitude];
    CLLocationDistance distance = [loc distanceFromLocation:userLocation];

    NSLog(@"Distance from Annotations - %f", distance);

    [distances setObject:obj forKey:@( distance )];
}

NSArray *sortedKeys = [[distances allKeys] sortedArrayUsingSelector:@selector(compare:)];
NSArray *closestKeys = [sortedKeys subarrayWithRange:NSMakeRange(0, MIN(3, sortedKeys.count))];

NSArray *closestAnnotations = [distances objectsForKeys:closestKeys notFoundMarker:[NSNull null]];