Question

我有一个注释数组。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，如何从这些距离找到3个最接近的注释？

以下是我如何计算从用户位置到注释的距离。

  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，因此不要每次在循环中重新创建它。您也可以直接获取位置：

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

然后，您可以执行类似操作，将距离编号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，然后您就可以获得与前3个键相关联的注释。

假设您在运行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]];

Answer 2

NSArray *numbers = [NSArray arrayWithObjects:
                    [NSNumber numberWithInt:0],
                    [NSNumber numberWithInt:3],
                    [NSNumber numberWithInt:2],
                    [NSNumber numberWithInt:8],
                    nil];

NSSortDescriptor* sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:nil ascending:YES selector:@selector(localizedCompare:)];
NSArray *sortedNumbers = [numbers sortedArrayUsingDescriptors:[NSArray arrayWithObject:sortDescriptor]];

您将所有距离存储在一个数组中并对其进行排序，然后在那里拾取数字

[sortedNumbers objectAtIndex:0];
[sortedNumbers objectAtIndex:1];
[sortedNumbers objectAtIndex:2];

从用户位置ios查找最近的注释？

2 个答案: