core-data - 将 uiimageview 保存为 coredata 作为二进制数据 swift (5)

Question

我正在尝试将 imageview 作为图像保存到核心数据中的二进制数据中。我的代码不起作用。它有一个编译错误。在视图控制器中，它没有注册 cdHandler。我想要做的就是将 imaveview 保存为核心数据模型中的二进制数据。我有 2 个类，一个应用程序委托和一个视图控制器。

类视图控制器

    import UIKit
import CoreData

class ViewController: UIViewController {
var canVasView = UIImageView()
@objc func hhh() {
    let photo = self.canVasView.image
    let data = photo!.pngData()

    if cdHandler.saveObject(pic:  data!){
    }
}
}

应用程序代表

  import UIKit
import CoreData

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

var window: UIWindow?


     lazy var persistentContainer: NSPersistentContainer = {
         /*
          The persistent container for the application. This implementation
          creates and returns a container, having loaded the store for the
          application to it. This property is optional since there are legitimate
          error conditions that could cause the creation of the store to fail.
          */
         let container = NSPersistentContainer(name: "Model")
         container.loadPersistentStores(completionHandler: { (storeDescription, error) in
             if let error = error as NSError? {
                 // Replace this implementation with code to handle the error appropriately.
                 // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.

            /*
             Typical reasons for an error here include:
             * The parent directory does not exist, cannot be created, or disallows writing.
             * The persistent store is not accessible, due to permissions or data protection when the device is locked.
             * The device is out of space.
             * The store could not be migrated to the current model version.
             Check the error message to determine what the actual problem was.
             */
            fatalError("Unresolved error \(error), \(error.userInfo)")
        }
    })
    return container
}()
class cdHandler: NSObject {

    private class func getContext() -> NSManagedObjectContext {
        let appdeleagetzz = UIApplication.shared.delegate as! AppDelegate
        return appdeleagetzz.persistentContainer.viewContext
    }
    class func saveObject(pic: Data, userName: String) -> Bool {
        let context = getContext()
        let entity = NSEntityDescription.entity(forEntityName: "User", in: context)
        let managedObject = NSManagedObject(entity: entity!, insertInto: context)
        managedObject.setValue(pic, forKey:"pic")
        managedObject.setValue(userName, forKey:"userName")
        do {
            try context.save()
            return true

        } catch {
            return false

        }
    }
    class func deletObject(user: User) -> Bool {
        let context = getContext()
        context.delete(user)

        do {
            try context.save()
            return true
        } catch {
            return false

        }
    }

    class func fetchObject() -> [User]? {

        do {
            let context = getContext()
            return try context.fetch(User.fetchRequest())
        } catch {
            return [User]()
        }
    }

}
}

标签： core-dataimageviewappdelegatebinary-dataswift5

Answer 1

错误消息，*“AppDelegate”类型的值没有名为“persistentContainer”的成员，解释了问题。事实上，当我查看您的AppDelegate类的代码时，我可以确认它没有名为“persistentContainer”的成员。（如果我没看错的话，文件中的最后两行是大括号。第一行关闭你的cdHandler嵌套类，第二行关闭你的AppDelegate类。）

做以下练习。在 Xcode 中，单击菜单：File > New Project并选择iOS、Application和Single View App。将您的新项目命名为 Junk。打开核心数据复选框。单击按钮创建。完成后，查看 Xcode 创建的 AppDelegate.swift，在AppDelegate类中，您会看到它包含 8 个函数 ( func)。第 7 个是lazy var persistentContainer. 啊哈！编译器告诉您，您可能不应该删除这 8 个函数，persistentContainer尤其是.

您应该将该persistentContainer功能从该垃圾项目复制到AppDelegate您实际项目中的类中。或者，为了避免未来的麻烦，也可以考虑复制其他 7 个函数中的大部分。正如你所看到的，他们中的大多数除了提供对初学者有用的解释之外什么都不做。完成复制后，关闭Junk项目。（我在一个典型的一周内多次用一个新的垃圾项目覆盖我的垃圾项目，尤其是在回答 StackOverflow 问题时。）

这应该可以解决这个特定的错误并回答这个问题。继续下一期。:)

回复您仍然收到cdHandler 错误的评论

没有其他事情可做，我认为您所指的错误是仍然在您的屏幕截图中的编译器错误。换句话说，您是说添加persistentContainer定义并没有使它变得更好。

好吧，它对我有用。请用以下代码替换AppDelegate.swift类中的所有代码，构建并运行它...</p>

import UIKit
import CoreData

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        AppDelegate.cdHandler.testGetContext()
        return true
    }

    lazy var persistentContainer: NSPersistentContainer = {
        /*
         The persistent container for the application. This implementation
         creates and returns a container, having loaded the store for the
         application to it. This property is optional since there are legitimate
         error conditions that could cause the creation of the store to fail.
         */
        let container = NSPersistentContainer(name: "Junk")
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.

                /*
                 Typical reasons for an error here include:
                 * The parent directory does not exist, cannot be created, or disallows writing.
                 * The persistent store is not accessible, due to permissions or data protection when the device is locked.
                 * The device is out of space.
                 * The store could not be migrated to the current model version.
                 Check the error message to determine what the actual problem was.
                 */
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
        return container
    }()

    class cdHandler: NSObject {

        private class func getContext() -> NSManagedObjectContext {
            let appdeleagetzz = UIApplication.shared.delegate as! AppDelegate
            return appdeleagetzz.persistentContainer.viewContext
        }

        class func testGetContext() {
            let context = getContext()
            print("getContext() succeeded, got \(context)")
        }

        class func saveObject(pic: Data, userName: String) -> Bool {
            let context = getContext()
            let entity = NSEntityDescription.entity(forEntityName: "User", in: context)
            let managedObject = NSManagedObject(entity: entity!, insertInto: context)
            managedObject.setValue(pic, forKey:"pic")
            managedObject.setValue(userName, forKey:"userName")
            do {
                try context.save()
                return true

            } catch {
                return false

            }
        }
        class func deletObject(user: NSManagedObject) -> Bool {
            let context = getContext()
            context.delete(user)

            do {
                try context.save()
                return true
            } catch {
                return false

            }
        }

    }
}

你会看到编译没有错误。此外，它运行并且 AppDelegate.cdhandler.getContext() 方法有效。如您所见，在AppDelegate.application(application:didFinishLaunchingWithOptions:), I have added a call to a new method which I defined later,AppDelegate.cdHandler.testGetContext()` 中。它完美地工作。

你现在得到一个不同的错误吗？如果是这样，您需要指定它是构建错误还是运行错误。无论哪种情况，请将错误文本复制并粘贴到您的问题中，并告诉我们错误发生的位置。