swift - 将图像存储在 swift 的 Core Data 中

Question

我正在尝试将应用程序中的本地镜像保存到核心数据模型。我已经创建了实体并为图像创建了属性。但是当我运行该应用程序时，它崩溃并出现此错误，Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unacceptable type of value for attribute: property = "image"; desired type = NSData; given type = UIImage; value = <UIImage:我保存图像的代码是，

 let appDelegate = UIApplication.shared.delegate as! AppDelegate
    let context = appDelegate.persistentContainer.viewContext
    let entity = NSEntityDescription.entity(forEntityName: "Saloon", in: context)
    let newUser = NSManagedObject(entity: entity!, insertInto: context)

    newUser.setValue(nameLbl.text, forKey: "name")
    newUser.setValue(addressLbl.text, forKey: "address")
    newUser.setValue(distanceLbl.text, forKey: "distance")
    newUser.setValue(rating.text, forKey: "rating")
    newUser.setValue(imageView.image, forKey: "image") as? UIImage
 do {
        try context.save()
        print("saved")
    } catch {
        print("Failed saving")
    }

这就是我获取图像的方式，

let appDelegate = UIApplication.shared.delegate as! AppDelegate
    let context = appDelegate.persistentContainer.viewContext
    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Saloon")
    //request.predicate = NSPredicate(format: "age = %@", "12")
    request.returnsObjectsAsFaults = false
    do {
        let result = try context.fetch(request)
        for data in result as! [NSManagedObject] {

            print(data.value(forKey: "name") as! String)
            let image: Data = data.value(forKey: "image")! as! Data
            let decodedimage = UIImage(data: image)
            imageView2.image = decodedimage
            name2Lbl.text = data.value(forKey: "name") as? String
            address2Lbl.text = data.value(forKey: "address") as? String
            distance2Lbl.text = data.value(forKey: "distance") as? String
            rating2Lbl.text = data.value(forKey: "rating") as? String
        }

    } catch {

        print("Failed")
    }

Answer 1

您无法将 UIImage 直接保存在 Core Data 中。相反，您必须将图像转换为 NSData (如错误消息中的“desired type = NSData”)。这是一个 UIImage 扩展:

extension UIImage {
    func jpegData(withCompressionQuality quality: CGFloat) -> Data? {
        return autoreleasepool(invoking: {() -> Data? in
            return UIImageJPEGRepresentation(self, quality)
        })
    }
}

quality 是一个从 0.0 到 1.0 的值，后者代表 JPEG 压缩图像的最大质量。使用 autoreleasepool 有助于避免使用 UIImageJPEGRepresentation 时偶尔出现的内存泄漏问题。

然后您可以使用以下代码保存图像:

if let imageData = imageView.image .jpegData(withCompressionQuality: 1.0) {
    newUser.setValue(imageData, forKey: "image")
}

顺便说一句，如果您需要的话，您还可以转换为 PNG 而不是无损的 JPEG。使用 UIImagePNGRepresentation 而不是 UIImageJPEGRepresentation。