Swift NSPredicate与枚举参数

Question

我正在尝试检索SISLItem对象，通过谓词过滤它们，谓词用“IN”聚合参数。

SISLItem类

import Foundation
import CoreData

@objc(SISLItem)

class SISLItem: NSManagedObject {

  @NSManaged var needDate: NSDate?
  @NSManaged var purchaseStatus: NSNumber
  @NSManaged var isProposed: NSNumber
  @NSManaged var slEntry: SISLEntry?

}

SISLItem扩展

import Foundation
import CoreData

extension SISLItem {

  //  MARK: - Variables

  enum PurchaseStatus: Int16 {
    case
      Cancelled = -1,
      Open,
      OnHold,
      Purchased,
      Expired
  }
  …

稍后，我使用它来在扩展名中创建谓词。

…
var error: NSError?
let filterStatus: [Int16] = [SISLItem.PurchaseStatus.Open.rawValue, SISLItem.PurchaseStatus.OnHold.rawValue]
let predicate: NSPredicate = NSPredicate(format: "\(SISLItem.Attribute.PurchaseStatus.name) IN %@“, argumentArray: filterStatus)
let result: [SISLItem] = CoreDataHelper.searchObjectsWithPredicate(entityName: SISLItem.entityName(), predicate: predicate, sortKey: "\(SISLItem.Attribute.ShopListEntry.name).\(SISLEntry.Attribute.Name.name)", sortAscending: true, error: &error) as! [SISLItem]
…

我收到以下错误消息：

/Users/rs186096/Documents/OneDrive/Entwicklung/XCode/Shop It/Shop It/SISLItemExt.swift:66:36: Cannot find an initializer for type ‘NSPredicate' that accepts an argument list of type '(format: String, argumentArray: [Int16])'

用 0 ， 1 等整数值替换 filterStatus 中的枚举值不会导致此错误：

let filterStatus = [0, 1]

更新

将枚举类型更改为 Int ，它可以工作：

enum PurchaseStatus: Int {
…
let filterStatus: [Int] = [SISLItem.PurchaseStatus.Open.rawValue, SISLItem.PurchaseStatus.OnHold.rawValue]

使用特定的整数类型是谓词的已知限制吗？