segueing 时的核心数据错误：无法在 NSManagedObject 类上调用指定的初始化程序

Posted 2023-03-11

【中文标题】segueing 时的核心数据错误：无法在 NSManagedObject 类上调用指定的初始化程序

【英文标题】：Core Data Error when segueing: Failed to call designated initializer on NSManagedObject class

【发布时间】：2017-12-13 23:03:06

【问题描述】：

当点击 mapView 上的 pin 时，我有一个视图控制器会连接到另一个视图控制器。 “Pin”是一个 NSManagedObject，它在发送到第二个视图控制器（其中一个函数用实际图像填充它）之前填充了纬度和经度。

在我的 didSelect 函数完成后和调用 performSegue 函数之前，我收到错误“CoreData：错误：无法在 NSManagedObject 类 'Pin' 上调用指定的初始化程序”。

@nonobjc public class func fetchRequest() -> NSFetchRequest<Pin> 
    return NSFetchRequest<Pin>(entityName: "Pin")


@NSManaged public var latitude: Double
@NSManaged public var longitude: Double
@NSManaged public var images: NSSet?

这是类：

convenience init(latitude: Double, longitude: Double, context: NSManagedObjectContext) 
    if let entity = NSEntityDescription.entity(forEntityName: "Pin", in: context) 
        self.init(entity: entity, insertInto: context)
        self.latitude = latitude
        self.longitude = longitude
     else 
        fatalError("Unable to find entity name")
    

我尝试将 pin 声明为可选并强制使用“！”声明它。这两个选项都不起作用。根据我在网上学习和阅读的许多帖子，我需要使用指定的初始化程序来初始化 pin 变量。这是我在视图控制器类顶部的尝试，但它也不起作用。

var pin = Pin.init(entity: NSEntityDescription.entity(forEntityName: "Pin", in: CoreDataStack.sharedInstance().context)!, insertInto: CoreDataStack.sharedInstance().context)

创建图钉：

    // Create the annotation
    let touchPoint = gestureRecognizer.location(in: mapView)
    let newCoordinate = self.mapView.convert(touchPoint, toCoordinateFrom:self.mapView)
    let annotation = MKPointAnnotation()
    annotation.coordinate = newCoordinate


    pin = Pin(latitude: annotation.coordinate.latitude, longitude: annotation.coordinate.longitude, context: CoreDataStack.sharedInstance().context)
    let pinAnnotation = PinAnnotation(objectID: pin.objectID, title: nil, subtitle: nil, coordinate: annotation.coordinate)

    // Add the annotation
    mapView.addAnnotation(pinAnnotation)
    CoreDataStack.sharedInstance().saveContext()

在 didSelect 中选择引脚：

do 
        let pinAnnotation = view.annotation as! PinAnnotation
        let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Pin")
        let predicate = NSPredicate(format: "latitude == %@ AND longitude == %@", argumentArray: [pinAnnotation.coordinate.latitude, pinAnnotation.coordinate.longitude])
        fetchRequest.predicate = predicate
        let pins = try CoreDataStack.sharedInstance().context.fetch(fetchRequest) as? [Pin]
        pin = pins![0]
     catch let error as NSError 
        print("failed to get pin by object id")
        print(error.localizedDescription)
        return
    
        self.performSegue(withIdentifier: "collectionViewSegue", sender: self)

...并执行转场：

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) 
    if segue.identifier == "collectionViewSegue" 
        let controller = segue.destination as! CollectionViewController
        print("CoreDataStack context in segue= \(CoreDataStack.sharedInstance().context)")
            controller.selectedPin = pin
            if let images = pin.images?.allObjects as? [Images] 
                controller.photos = images
            
        print("PrepareForSegue pin properties are: \n latitude: \(pin.latitude) \n longitude: \(pin.longitude)")
        

我错过了什么？

【参考方案1】：

我通过在课程开始时将变量声明设为可选来解决了这个问题：

var selectedPin: Pin?

...并在我的长按手势识别器功能中进行不同的初始化：

    @objc func handleLongPress(_ gestureRecognizer : UIGestureRecognizer) 
    if gestureRecognizer.state != .began  return 
    print("Tap gesture recognized")

    // Create the annotation
    let touchPoint = gestureRecognizer.location(in: mapView)
    let newCoordinate = self.mapView.convert(touchPoint, toCoordinateFrom:self.mapView)
    let annotation = MKPointAnnotation()
    annotation.coordinate = newCoordinate

    // Initialize NSManagedObject 'Pin' with properties
    selectedPin = Pin(context: CoreDataStack.sharedInstance().context)
    selectedPin?.latitude = annotation.coordinate.latitude
    selectedPin?.longitude = annotation.coordinate.longitude

    if let selectedPin = selectedPin 
    let pinAnnotation = PinAnnotation(objectID: selectedPin.objectID, title: nil, subtitle: nil, coordinate: annotation.coordinate)

    // Add the annotation
    mapView.addAnnotation(pinAnnotation)
    

    CoreDataStack.sharedInstance().saveContext()
    print("This is what the ole save looks like: \(CoreDataStack.sharedInstance().context)")