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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，我怎样才能找到这些距离中最近的 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);


    }
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2 回答 2

2

这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。

Assuming that you always have at least one annotation when you run this:

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]];
于 2014-03-17T11:01:08.423 回答
1 
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，然后在顶部选择数字

[sortedNumbers objectAtIndex:0];
[sortedNumbers objectAtIndex:1];
[sortedNumbers objectAtIndex:2];
于 2014-03-17T11:00:36.500 回答