ios - 尝试转换为NSFetchedResultsController“严重错误:在展开可选值时意外发现nil”？

我正在尝试使用NSFetchedResultsController将工作表视图转换为表视图。

我仅测试两个条目，这是我的工作代码的一部分

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
let fetchRequest = NSFetchRequest(entityName: "Appointments")
        //3
        do {
            self.tableView.reloadData()
            let results = try context.executeFetchRequest(fetchRequest)
            invoices = results as Array<AnyObject>  //cast to Appointments didn't work
        } catch let error as NSError {
            print("Could not fetch \(error), \(error.userInfo)")
        }

这是我转换代码的一部分

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

var frc: NSFetchedResultsController = NSFetchedResultsController()

func getFetchedResultsController()->NSFetchedResultsController {
    frc = NSFetchedResultsController(fetchRequest: listFetchRequest(), managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    return frc
}

func listFetchRequest()->NSFetchRequest{
    let fetchRequest = NSFetchRequest(entityName: "Appointments")
    let sortDescriptor = NSSortDescriptor(key: "appointmentUser", ascending: true)
    fetchRequest.sortDescriptors = [sortDescriptor]
    return fetchRequest
}

var appointments = [AnyObject]()//[NSManagedObject]()

它构建成功，但是我直接收到错误消息：
致命错误：解开Optional值时意外发现nil

libswiftCore.dylib`function signature specialization <Arg[0] = Exploded, Arg[1] = Exploded, Arg[2] = Dead, Arg[3] = Dead> of Swift._fatalErrorMessage (Swift.StaticString, Swift.StaticString, Swift.StaticString, Swift.UInt) -> ():
0x1002c0a50 <+0>:   stp    x29, x30, [sp, #-16]!
0x1002c0a54 <+4>:   mov    x29, sp
0x1002c0a58 <+8>:   sub    sp, sp, #16
0x1002c0a5c <+12>:  and    w8, w2, #0x1
0x1002c0a60 <+16>:  tbnz   w8, #0, 0x1002c0a80       ; <+48>
0x1002c0a64 <+20>:  tbnz   x1, #63, 0x1002c0ac4      ; <+116>
0x1002c0a68 <+24>:  add    x1, x0, x1
0x1002c0a6c <+28>:  mov    x2, x3
0x1002c0a70 <+32>:  mov    x3, x4
    0x1002c0a74 <+36>:  mov    x4, x5
    0x1002c0a78 <+40>:  bl     0x10030d910               ; function signature specialization <Arg[0] = Exploded, Arg[1] = Exploded> of Swift.(_fatalErrorMessage (Swift.StaticString, Swift.StaticString, Swift.StaticString, Swift.UInt) -> ()).(closure #2)
->  0x1002c0a7c <+44>:  brk    #0x1
    0x1002c0a80 <+48>:  str    xzr, [sp, #8]
    0x1002c0a84 <+52>:  cmp    x0, w0, uxtw

我如何检查展开的位置？我怎样才能解决这个问题？

[编辑]
通过一些反复试验（即将淘汰的部分），我认为这与代码的这一部分有关

        override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        // #warning Incomplete implementation, return the number of sections
//        return 1
        let numberOfSections = frc.sections?.count
        return numberOfSections!
    }

另请参见：NSFetchedResultsController swift sections

最佳答案

问题出在这段代码上：

// issue 1
var frc: NSFetchedResultsController = NSFetchedResultsController()

// issue 2
func getFetchedResultsController()->NSFetchedResultsController {
    frc = NSFetchedResultsController(fetchRequest: listFetchRequest(), managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    return frc
}

问题1：正在实例化（但未配置）NSFetchedResultsController，并将其存储在frc中。

问题2：每次调用该函数时，都会创建一个新的，已配置的NSFetchedResultsController（并将其存储在frc中）。

我认为您要在此处实现的是延迟实例化，删除getFetchedResultsController函数并用以下代码替换变量声明：

lazy var frc: NSFetchedResultsController = {
    let fetchedResultsController = NSFetchedResultsController(fetchRequest: self.listFetchRequest(), managedObjectContext: self.context, sectionNameKeyPath: nil, cacheName: nil)
    fetchedResultsController.delegate = self
    return fetchedResultsController
}()

首次访问frc属性时，这将设置获取的结果控制器，并将委托分配为self。

根据您的评论，viewDidLoad方法将如下所示：

override func viewDidLoad() {
    super.viewDidLoad()

    do {
        try self.frc.performFetch()
    } catch {
        ...
    }
}

关于ios - 尝试转换为NSFetchedResultsController“严重错误:在展开可选值时意外发现nil”？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/33279511/