保存核心数据属性时，将索引从 0 移动到 1

Question

下面的 swift 代码将 2 张图像保存到二进制核心数据中。当用户在文本字段中输入 1 或 0 时，图像视图将获取数据并显示。我想将索引移动到从 1 开始而不是从 0 开始。当用户在文本字段中输入 0 时，图像视图中的任何内容都不应显示。在我的核心数据模型中，图片是二进制数据。

import UIKit
import CoreData
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 = 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)
}
}
}

Answer 1

你可以做的是调用index - 1

当用户在文本字段中输入 0 时，imageview中的任何内容都不会显示，因为索引 - 1 变为 -1 并且NSPredicate(format: "idx == %d", Int32(index))返回 nil

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
}

希望对您有所帮助=(快乐编码

或者您可以做的是在删除应用程序后相应地将索引保存在coredata

中

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)
}
}