Question

所以我正在制作这个xCode项目，用Swift语言编写iPhone应用程序。我试图在核心数据的对象中存储两个字符串和二进制数据图像，我可以在此viewcontroller中检索。我用来转换到此视图的表格视图显示正确的项目关联，但是当我加载此视图时，属性不会加载。为什么对象没有上传并显示到viewcontroller？

import UIKit
import CoreData

class IndividualMainViewController: UIViewController, NSFetchedResultsControllerDelegate, UIImagePickerControllerDelegate, UINavigationControllerDelegate
{

    @IBOutlet weak var backCancelButton: UIBarButtonItem!
    @IBOutlet weak var saveEditButton: UIBarButtonItem!

    @IBOutlet weak var deviceImageButton: UIButton!
    @IBOutlet weak var cameraImageButton: UIButton!


    var item: Item? = nil
    let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
    let frc: NSFetchedResultsController = NSFetchedResultsController()


    @IBOutlet weak var imageHolder: UIImageView!

    @IBOutlet weak var horseName: UITextField!
    @IBOutlet weak var officialName: UITextField!

    override func viewDidLoad()
    {
        super.viewDidLoad()


        if(item == nil)
        {
            print("item returned nil")
            print(item)
        }
        else
        {
            print("Object did load")
            self.horseName.text = item?.name
            self.officialName.text = item?.offName
            self.imageHolder.image = UIImage(data: (item?.image)!)

            saveEditButton.title = "Edit"
            backCancelButton.title = "To Barn"

            self.deviceImageButton.hidden = true

            self.cameraImageButton.hidden = true

        }

        let tap: UIGestureRecognizer = UITapGestureRecognizer(target: self, action: "dismissEditor")
        view.addGestureRecognizer(tap)


    }

    override func didReceiveMemoryWarning()
    {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func dismissEditor()
    {
        view.endEditing(true)
    }



    @IBAction func addImageFromDevice(sender: AnyObject)
    {
        let pickerController = UIImagePickerController()
        pickerController.delegate = self
        pickerController.sourceType = UIImagePickerControllerSourceType.PhotoLibrary
        pickerController.allowsEditing = true

        self.presentViewController(pickerController, animated: true, completion: nil)
    }


    @IBAction func addImageFromCamera(sender: AnyObject)
    {
        let pickerController = UIImagePickerController()
        pickerController.delegate = self
        pickerController.sourceType = UIImagePickerControllerSourceType.Camera
        pickerController.allowsEditing = true

        self.presentViewController(pickerController, animated: true, completion: nil)
    }

    func imagePickerController(picker: UIImagePickerController, didFinishPickingImage image: UIImage, editingInfo: [String : AnyObject]?)
    {
        self.dismissViewControllerAnimated(true, completion: nil)

        self.imageHolder.image = image
    }



    @IBAction func saveEditTapped(sender: AnyObject)
    {
        if(saveEditButton.title == "Save")
        {
            if item != nil
            {
                editItem()

                print("Item edit saved")

                saveEditButton.title = "Edit"
                backCancelButton.title = "To Barn"
            }
            else
            {
                createNewItem()

                print("New item created")

                performSegueWithIdentifier("back", sender: nil)
            }
        }
        else
        {
            saveEditButton.title = "Save"
            backCancelButton.title = "Cancel"
            print("Not saved")
        }
    }



    func createNewItem()
    {
        let entityDescription = NSEntityDescription.entityForName("Item", inManagedObjectContext: moc)

        let item = Item(entity: entityDescription!, insertIntoManagedObjectContext: moc)

        item.name = horseName.text
        item.offName = officialName.text
        item.image = UIImagePNGRepresentation(imageHolder.image!)

        do
        {
            try self.moc.save()
        }
        catch
        {
            print("Failed ot create new object")
            return
        }
    }



    func editItem()
    {
        item?.name = horseName.text
        item?.offName = officialName.text
        item!.image = UIImagePNGRepresentation(imageHolder.image!)

        do
        {
            try self.moc.save()
        }
        catch
        {
            print("Failed to save item")
            return
        }
    }
}

Answer 1

仅使用通用初始化程序初始化NSFetchedResultsController是不够的。

您必须告诉控制器要执行的操作，使用哪个托管对象上下文，设置委托并执行初始提取。

Swift中的常用方法是将控制器声明为惰性计算变量。

lazy var fetchedResultsController: NSFetchedResultsController = {

  let fetchRequest = NSFetchRequest()
  let entity = NSEntityDescription.entityForName(self.entity, inManagedObjectContext: self.managedObjectContext)
  fetchRequest.entity = entity
  fetchRequest.predicate = self.fetchPredicate

  // Set the batch size to a suitable number.
  fetchRequest.fetchBatchSize = 20

  // Edit the sort key as appropriate.
  fetchRequest.sortDescriptors = [self.sortDescriptor]

  // Edit the section name key path and cache name if appropriate.
  // nil for section name key path means "no sections".
  let aFetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.managedObjectContext!, sectionNameKeyPath: nil, cacheName: nil)
  aFetchedResultsController.delegate = self

  do {
    try aFetchedResultsController.performFetch()
  } catch let error as NSError {
    print(error)
  }

  return aFetchedResultsController
}()

将实例变量（以self.开头）表示的所有参数替换为值

为什么我的视图控制器无法检索到我的CoreData对象

1 个答案: