Question

所以我有一个带有纬度和经度值的点数据集，我想检索它们并按照到用户当前位置的距离对它们进行排序。目前，我有以下内容：

mainMoc.performBlockAndWait {
            // Fetching data from CoreData
            let fetchRequest = NSFetchRequest()
            fetchRequest.predicate = NSPredicate(format: "pointLatitude BETWEEN {%f,%f} AND pointLongitude BETWEEN {%f,%f}", (latitude-0.03), (latitude+0.03), (longitude-0.03), (longitude+0.03))
            let entity = NSEntityDescription.entityForName("PointPrimary", inManagedObjectContext: self.mainMoc)
            fetchRequest.entity = entity

            let sortDescriptor = NSSortDescriptor(key: "pointTitle", ascending: false)
            fetchRequest.sortDescriptors = [sortDescriptor]

            do {
                points = try self.mainMoc.executeFetchRequest(fetchRequest) as! [PointPrimary]

            } catch {
                let jsonError = error as NSError
                NSLog("\(jsonError), \(jsonError.localizedDescription)")
                abort()
            }
        }

所以目前我只根据标题对其进行排序。但是，如果我想计算一个CLLocationCoordinate2D的距离并根据它来对fetchRequest结果进行排序，我将如何继续？

非常感谢！

Answer 1

这应该有效。基本上，您将NSSortDescriptor与自定义比较器一起使用。

诀窍是使用"self"作为NSSortDescriptor的键，它将获取的对象传递给比较器。

var userLocation : CLLocation // get that from somewhere
var distanceCompare : NSComparator = {
    (obj1: AnyObject!, obj2: AnyObject!) -> NSComparisonResult in
    let lng1 = obj1.valueForKey("pointLongitude") as! CLLocationDegrees
    let lat1 = obj1.valueForKey("pointLatitude") as! CLLocationDegrees
    let p1Location : CLLocation = CLLocation(latitude: lat1, longitude: lng1)
    let p1DistanceToUserLocation = userLocation.distanceFromLocation(p1Location)

    let lng2 = obj2.valueForKey("pointLongitude") as! CLLocationDegrees
    let lat2 = obj2.valueForKey("pointLatitude") as! CLLocationDegrees
    let p2Location : CLLocation = CLLocation(latitude: lat1, longitude: lng1)
    let p2DistanceToUserLocation = userLocation.distanceFromLocation(p2Location)

    if (p1DistanceToUserLocation > p2DistanceToUserLocation) {
        return .OrderedDescending
    } else if (p1DistanceToUserLocation < p2DistanceToUserLocation) {
        return .OrderedAscending
    } else {
        return .OrderedSame
    }
}

var distanceSortDescriptor = NSSortDescriptor(key: "self", ascending: true, comparator: distanceCompare)
fetchRequest.sortDescriptors = [distanceSortDescriptor]

Answer 2

NSFetchRequest不能使用模型中定义的属性（并存储在数据库中）作为排序描述符，因此您不得不求助于内存中排序。在distance类上定义执行适当计算的PointPrimary方法并执行：

let sortedPoints = points.sortedArrayUsingDescriptors([NSSortDescriptor(key: "distance", ascending: true)])

按计算结果

2 个答案: