调用时未在 UIImageView 中获取二进制数据

Question

我下面的 swift 代码使用文本字段输入数字。当应用程序构建时，2 个图像被保存到核心数据二进制数据图像。有一个索引连接到它来控制图像保存方式的顺序。当用户在文本字段中输入 1 时，输入 2 时应该出现第一个图像。下面是我想要实现的gif。

导入 UIKit 导入核心数据

class ViewController: UIViewController,UITextFieldDelegate {


    @IBOutlet var labelName : UILabel!
    @IBOutlet var enterT : UITextField!
    @IBOutlet var pic : UIImageView!
    lazy var context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext


    var dx = [UIImage]()
    var names = [String]()

    override func viewDidLoad() {
        super.viewDidLoad()


        enterT.delegate = self

        pic.backgroundColor = .cyan


        guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
        let managedContext = appDelegate.persistentContainer.viewContext
        let entity = NSEntityDescription.entity(forEntityName: "Users", in: managedContext)!
        let item = NSManagedObject(entity: entity, insertInto: managedContext)
             let item2 = NSManagedObject(entity: entity, insertInto: managedContext)
        let fetch = NSFetchRequest<NSFetchRequestResult>(entityName: "Users")

        let vex = UIImage(named: "on.jpg")?.pngData()
        if let data = vex{
            item.setValue(data, forKey: "image")

        }




        let vex2 = UIImage(named: "house.jpg")?.pngData()
        if let data2 = vex2{
            item2.setValue(data2, forKey: "image")
        }




             do {
                 let result = try? managedContext.fetch(fetch) as? [Users]
                 print("Queen",result?.count)
                 try? managedContext.save()



             }
             catch {
                 print("Could not save")
             }


    }


    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

        guard let text = (textField.text as? NSString)?.replacingCharacters(in: range, with: string), let index = Int(text) else { //here....
            // display an alert about invalid text
            return true
        }
        save(at: index )
        return true
    }

    func save(at index : Int) {
        let fetchRequest = NSFetchRequest<Users>(entityName: "Users")
        fetchRequest.predicate = NSPredicate(format: "idx == %d", Int32(index))
        do {
            if let user = try context.fetch(fetchRequest).first {


                pic.image = UIImage(data: user.image ?? Data())
            }
        } catch {
            print("Could not fetch \(error) ")
        }
        return
    }

    @IBAction func add(){


        fetch()
    }



    func fetch()
    {



        for i in 0..<dx.count {
            let newUser = Users(context: context)
            newUser.image = dx[i].jpegData(compressionQuality: 1)
            newUser.idx = Int32(i + 1)


        }



        print("Storing Data..")
        do {
            try context.save()
        } catch {
            print("Storing data Failed", error)
        }
        return
    }


}

Answer 1

您混淆了获取和节省

当您将项目添加到数据库时，创建对象并保存上下文。不取。
当您从数据库加载项目时获取记录。不保存。

我不知道 shouldChangeCharactersIn 是否按预期工作。其他代码应该可以工作。

再一次，在每次启动应用程序时，（相同的）两项都会再次添加到数据库中。

注意这一点。如果项目存在，请删除或注释掉 viewDidLoad.

中的行 populateData()

class ViewController: UIViewController,UITextFieldDelegate {


    @IBOutlet var labelName : UILabel!
    @IBOutlet var enterT : UITextField!
    @IBOutlet var pic : UIImageView!
    lazy var context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

    override func viewDidLoad() {
        super.viewDidLoad()

        enterT.delegate = self

        pic.backgroundColor = .cyan
        populateData()
    }


    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

        guard let text = (textField.text as? NSString)?.replacingCharacters(in: range, with: string), let index = Int(text) else { //here....
            // display an alert about invalid text
            return true
        }
        loadImage(at: index )
        return true
    }

    func loadImage(at index : Int) {
        let fetchRequest = NSFetchRequest<Users>(entityName: "Users")
        fetchRequest.predicate = NSPredicate(format: "idx == %d", Int32(index))
        do {
            if let user = try context.fetch(fetchRequest).first {
                pic.image = UIImage(data: user.image!)
            } else {
               pic.image = nil
            }
        } catch {
            print("Could not fetch \(error) ")
        }
    }

    @IBAction func add(){
        // fetch()
    }

    func populateData()
    {
        let item = Users(context: context)
        let vex = UIImage(named: "on.jpg")!.pngData()
        item.image = vex
        item.idx = 1

        let item2 = Users(context: context)
        let vex2 = UIImage(named: "house.jpg")!.pngData()
        item2.image = vex2
        item2.idx = 2

        print("Storing Data..")
        do {
            try context.save()
        } catch {
            print("Storing data Failed", error)
        }
    }
}

调用时未在 UIImageView 中获取二进制数据

binary data not fetching in UIImageView when called

core-data

binary-data

fetch

uiimageview

swift