在CoreData中保存Swift CLLocation

Question

我正在尝试CLLocation在Core Data中保存数据.我的属性设置为可转换对象.

一些示例代码表明可以使用此objc转换为a来保存位置数据NSValue.

CLLocationCoordinate2D myLocation;
NSValue *locationValue = [NSValue valueWithBytes:&myLocation objCType:@encode(CLLocationCoordinate2D)]
// then put locationValue into storage - maybe an ObjC collection class or core data etc.

从数据存储中检索对象应该可以使用此范例.

CLLocationCoordinate2D myLocation;
NSValue *locationValue = // restored from your database or retrieved from your collection class
[locationValue getValue:&myLocation];

我试图推断这个想法并将整个CLLocation对象捕获到NSValue存储中CoreData,目标CLLocation是稍后从商店中恢复对象.

在测试各种方法时,我发现在尝试CLLocation从Core Data Store中解包对象时返回了nil .我CLLocation使用以下内容将对象放入商店:

//verified that I have a good CLLocation here
newManagedObject.setValue(location as CLLocation, forKey: "location")

后来我试图解开 CLLocation

let location = detail.valueForKey("location")! as CLLocation

但我发现该对象没有正确解开.

打开的对象看起来像:

(CLLocation) location = 0x00007fff59537c90 {
  ObjectiveC.NSObject = {}
}

因此,此时CLLocation对象的任何使用都会返回" found nil ... error "

我是否遗漏了CLLocation使用Swift 存储/检索对象的明显内容？

UPDATE

丹尼尔的回答让我意识到NSValueTransformer不适合我,所以我回到了以前用过的方法.基本上使用NSKeyedArchiver编码对象图.我的目标一如既往地使用最简单的解决方案,因此我选择不使用托管对象子类,因为我需要的属性已经存在于现有的CLLocation对象中.我选中了选项(存储在外部记录文件中),将可转换字段更改为二进制数据.我开始测试这个过程,只需对主细节模板进行微小的更改.

保存CLLocation对象图

//assuming location is a valid CLLocation and data model has a binary data field
let archivedLocation = NSKeyedArchiver.archivedDataWithRootObject(location)
newManagedObject.setValue(archivedLocation, forKey: "location")

从数据存储中恢复对象图

在主vc上作为默认的一部分准备segue,数据通过fetch控制器恢复.

let object = self.fetchedResultsController.objectAtIndexPath(indexPath) as NSManagedObject
let controller = (segue.destinationViewController as UINavigationController).topViewController as DetailViewController
                    controller.detailItem = object 

在详细的vc上,我使用NSKeyedUnarchiver打开我的对象图

var lc = NSKeyedUnarchiver.unarchiveObjectWithData(detail.valueForKey!("location") as NSData) as CLLocation

Answer 1

NSManagedObject为CLLocation对象创建子类时，麻烦会少很多。然后，为了方便起见，创建用于存储和检索的方法：

import Foundation
import CoreData
import CoreLocation

class LocationPoint: NSManagedObject {

    @NSManaged var latitude: NSNumber!
    @NSManaged var longitude: NSNumber!
    @NSManaged var altitude: NSNumber!
    @NSManaged var timestamp: NSDate!
    @NSManaged var horizontalAccuracy: NSNumber
    @NSManaged var verticalAccuracy: NSNumber
    @NSManaged var speed: NSNumber
    @NSManaged var course: NSNumber

    func initFromLocation(location: CLLocation) {
        self.latitude           = location.coordinate.latitude
        self.longitude          = location.coordinate.longitude
        self.altitude           = location.altitude
        self.timestamp          = location.timestamp

        self.horizontalAccuracy = location.horizontalAccuracy > 0.0 ? location.horizontalAccuracy : 0.0
        self.verticalAccuracy   = location.verticalAccuracy > 0.0 ? location.verticalAccuracy : 0.0
        self.speed              = location.speed > 0.0 ? location.speed : 0.0
        self.course             = location.course > 0.0 ? location.course : 0.0
    }

    func location() -> CLLocation {
        return CLLocation(
            coordinate: CLLocationCoordinate2D(latitude: self.latitude.doubleValue, longitude: self.longitude.doubleValue),
            altitude: self.altitude.doubleValue,
            horizontalAccuracy: self.horizontalAccuracy.doubleValue,
            verticalAccuracy: self.verticalAccuracy.doubleValue,
            course: self.course.doubleValue,
            speed: self.speed.doubleValue,
            timestamp: self.timestamp
        )
    }

您必须根据此类使用实体来设置数据模型。

Answer 2

您缺少的是 NSValue 用于存储类型，即连续的内存块，而不是对象。CLLocation 是一个对象。

为了在核心数据中存储 CLLocation，您必须存储每个属性。另一种方法是使用编码器。