Swift：executeFetchRequest：无法转换'Any Object'类型的值

Question

我有一些关于executeFetchRequest的问题

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 = ""
   }

但是这条线的错误

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

无法将['Any Object']类型的值转换为指定类型'Beacons'

请帮帮我谢谢:)）

Answer 1

两个问题：

• executeFetchRequest始终返回一个对象数组 。
• 你必须施放类型。

---

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

无法将类型的值...转换为指定的类型...通常意味着编译器需要通过转换类型来提供帮助，或者根本没有任何关系。

PS：建议以单数形式命名Core Data实体以避免混淆。