ios - Swift:executeFetchRequest:无法转换类型为 'Any Object' 的值

Question

我对 executeFetchRequest 有一些疑问

import UIKit
import CoreData

class BeaconDB: NSObject {

    var addStatus: BeaconAddStatus!


    enum BeaconAddStatus{
          case DUPLICATE_IN_AD
          case ADDED_SUCCESSFULL
          case ERROR_IN_ADD
     }


    func addNewBeacon(beacon: BeaconData) -> BeaconAddStatus{
          print("ADDNewBeacon")
          print("uuid: %@ \(beacon.uuid)")

    let appDelegate: AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let context: NSManagedObjectContext = appDelegate.managedObjectContext

    let entityDesc: NSEntityDescription = NSEntityDescription.entityForName("Beacon", inManagedObjectContext: context)!
    let request: NSFetchRequest = NSFetchRequest()
    let predSearch: NSPredicate = NSPredicate(format: "(uuid = %@) AND (major = %@) AND (minor = %@) \(beacon.uuid), \(beacon.major), \(beacon.minor)")

    request.entity = entityDesc
    request.predicate = predSearch

    do {
        let existingBeacon: Beacons = try context.executeFetchRequest(request)
        // success ...
    } catch let error as NSError {
        // failure
        print("Fetch failed: \(error.localizedDescription)")
    }

}

}

Mv Beacons 类是 NSManagedObject

  import UIKit

  import CoreData

  class Beacons: NSManagedObject {

      dynamic var major : NSNumber = 0.0
      dynamic var minor : NSNumber = 0.0
      dynamic var name : NSString = ""
      dynamic var uuid : NSString = ""
   }

但是这条线是错误的

 let existingBeacon: Beacons = try context.executeFetchRequest(request)

无法将类型 ['Any Object'] 的值转换为指定类型 'Beacons'

请帮帮我 谢谢:))

Answer 1

两个问题:

• executeFetchRequest 总是返回对象的数组。
• 你必须转换类型。

---

let existingBeacons = try context.executeFetchRequest(request) as! [Beacons]

无法将类型...的值转换为指定的类型... 意味着编译器通常需要通过转换类型来获得帮助，或者根本没有任何关系。

PS:建议以单数形式命名 Core Data 实体，以免混淆。