将图像保存到有序索引的二进制数据中

Question

下面我的快速代码试图将图片图像中的图像追加并保存到核心数据中。核心数据属性位于下面的图像中。当用户在文本字段中输入3时，将显示已保存到核心数据中的图像，因为这是索引中的顺序。构建时会保存2张图像，因此新图像应从索引的3开始。

import UIKit
 import CoreData
   class ViewController: UIViewController,UITextFieldDelegate, UIImagePickerControllerDelegate, UINavigationControllerDelegate {

  var imagePicker: UIImagePickerController!

@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 - 1 )
    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(){
      imagePicker =  UIImagePickerController()
    imagePicker.delegate = self
    imagePicker.sourceType = .photoLibrary
    present(imagePicker, animated: true, completion: nil)

}
@IBAction func append(){

}

func populateData()
{
    let item = Users(context: context)
    let vex = UIImage(named: "on.jpg")!.pngData()
    item.image = vex
    item.idx = 0

    let item2 = Users(context: context)
    let vex2 = UIImage(named: "house.jpg")!.pngData()
    item2.image = vex2
    item2.idx = 1

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


func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {

    // The info dictionary may contain multiple representations of the image. You want to use the original.
    guard let selectedImage = info[.originalImage] as? UIImage else {
        fatalError("Expected a dictionary containing an image, but was provided the following: \(info)")
    }

    // Set photoImageView to display the selected image.

    pic.image = selectedImage

    // Dismiss the picker.
    dismiss(animated: true, completion: nil)
}
@objc func image(_ image: UIImage, didFinishSavingWithError error: Error?, contextInfo: UnsafeRawPointer) {
    if let error = error {
        // we got back an error!
        let ac = UIAlertController(title: "Save error", message: error.localizedDescription, preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)
    } else {
        let ac = UIAlertController(title: "Saved!", message: "Your altered image has been saved to your photos.", preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)
    }
}
 }

Answer 1

看看方法populateData，有代码创建记录，为属性分配值并保存上下文。

如果要添加多个图像，则必须计算下一个可用索引。索引通常是已保存项目的数量。如果在索引0和1处有两个预定义图像，则下一个可用索引为2。

要动态获取获取的记录的数量，请创建一个获取请求并在上下文中调用count(for:

let fetchRequest = NSFetchRequest<Users>(entityName: "Users")
let nextAvailableIndex = try context.count(for: fetchRequest)