NSArray 不匹配 Swift 数组元素类型

Question

我正在尝试从 CoreData 在 UIPickerView 中显示项目。但我总是在pickerviews titleforrow 函数中得到NSArray element failed to match the Swift Array Element type。这是我的完整代码：

import Foundation
import UIKit
import CoreData

class Create_New: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate{
    var picker = UIPickerView()
    var picker2 = UIPickerView()
    var territory: [String] = []
    var company: [Company] = []
    var facility: [String] = []
    var specialty: [String] = []
    var a = 0, b = 0, c = 0, d = 0
    override func viewDidLoad() {
        super.viewDidLoad()
        picker.delegate = self
        picker.dataSource = self

        picker2.delegate = self
        picker2.dataSource = self

    }
    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)

        var appDel:AppDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
        var context:NSManagedObjectContext = appDel.managedObjectContext
        let fetchRequest = NSFetchRequest(entityName:"Company")
        let fetchRequestTerritory = NSFetchRequest(entityName:"Territory")
        let fetchRequestFacility = NSFetchRequest(entityName:"Facility")
        let fetchRequestSpecialty = NSFetchRequest(entityName:"Specialty")
        let error:NSError

        do {
            let company_temp = try context.executeFetchRequest(fetchRequest)

            company = company_temp as! [Company]
            a = company_temp.count
            print(company.count)

            let territory_temp = try context.executeFetchRequest(fetchRequestTerritory)
            territory = territory_temp.flatMap{ $0 as? String }
            b = territory_temp.count
            print(territory_temp.count)

            let facility_temp = try context.executeFetchRequest(fetchRequestFacility)
            facility = facility_temp.flatMap{ $0 as? String }
            c = facility_temp.count
            print(facility_temp.count)

            let specialty_temp = try context.executeFetchRequest(fetchRequestSpecialty)
            specialty = specialty_temp.flatMap{ $0 as? String }
            d = specialty.count
            print(specialty_temp.count)

        } catch let error as NSError {
            // failure
            print("Fetch failed: \(error.localizedDescription)")
        }


         }
    func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        var x = 1
        if (pickerView.tag == 1){
            //print(territory.count)
            return b
        }else if (pickerView.tag == 2){
            //print(company.count)
            return a
        }else if (pickerView.tag == 3){
            //print(facility.count)
            return c
        }else if (pickerView.tag == 4){
            //print(specialty.count)
            return d
        }
        return x
    }

    func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {


    }
    func pickerView(pickerView: UIPickerView, widthForComponent component: Int) -> CGFloat {
        return 200
    }

    func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        var temp: [String] = []
                if (pickerView.tag == 1){
            return  company[a-1].name! as String
        }else if (pickerView.tag == 2){
            return company[a-1].name
        }else if (pickerView.tag == 3){
            return company[a-1].name
        }else if (pickerView.tag == 4){
            return  company[a-1].name
        }
        return temp[row]
    }
} 

我当时想做的是从 Coredata 中获取一些记录并将它们放入一个数组中，就像您在我的变量声明中看到的一样。但我收到错误AnyObject cannot be converted to String。 对不起这个简单的问题。我是 Swift 和 iOS 开发的新手。

编辑： 我从这一行得到错误：return company[a-1].name! as String

这是我的公司课程：

import Foundation
import CoreData


class Company: NSManagedObject {

// Insert code here to add functionality to your managed object subclass

}

xc模型：

我刚刚从输出窗口中注意到了这段文字： 无法为实体“公司”加载名为“公司”的类。找不到类，改用默认的 NSManagedObject。

Answer 1

首先将数据模型文件中Company类的Module设置为Current Product Module

Company 中的属性name 似乎被声明为可选String，并且由于该方法还返回一个可选String，所以可能很简单

return company[a-1].name

Answer 2

as 强制转换只能用于保证成功的强制转换（我认为是从 Swift 1.2 开始）。如果你真的想强制强制转换，因为你知道它是有效的，你可以使用as!，但在这些情况下我总是使用as?，然后处理返回的可选值。

你可以改变：

 return company[a-1].name! as String

到：

return company[a-1].name as? String

因为该方法无论如何都会返回一个可选的。如果没有，您可以使用 nil-coalescing 处理 nil 情况：

return company[a-1].name as? String ?? "-"

其中“-”是一个合适的后备选项。