如何使用 Swift 删除 coredata 中的特定记录？

Question

我的场景是，我将 JSON 数据加载到 CoreData 中，然后我将其提取到 Tableview 中。现在，每个表格视图单元格都可以使用Delete 和Edit 按钮进行滑动。如果我点击删除，我需要从 coredata 和 tableview 这两个地方删除数据。

我的 JSON 结构

   class displyDataClass {
    var name : String
    var username : String
    var email : String

init(name : String,username : String,email :String) {
    self.name = name
    self.username = username
    self.email = email
   }
}

JSON 加载到 CoreData

import UIKit
import CoreData

class ViewController: UIViewController ,UITableViewDelegate,UITableViewDataSource{

var displayDatasssss = [displyDataClass]()
var context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

@IBOutlet weak var tableView: UITableView!

override func viewDidLoad() {
    super.viewDidLoad()
    print("hai")

    // Do any additional setup after loading the view, typically from a nib.
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}
func numberOfSections(in tableView: UITableView) -> Int {
    return 1
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return displayDatasssss.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "TableViewCell1") as! TableViewCell1





    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "User")
    cell.label.text = displayDatasssss[indexPath.row].email


    let _:AppDelegate = (UIApplication.shared.delegate as! AppDelegate)
    let context:NSManagedObjectContext = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
    let newUser = NSEntityDescription.insertNewObject(forEntityName: "User", into: context) as NSManagedObject
    newUser.setValue(cell.label.text, forKey: "name")

    do {
        try context.save()
    } catch {}
    print(newUser)
    print("Object Saved.")


    let myStringValue = cell.label.text
    request.predicate = NSPredicate (format: "name == %@", myStringValue!)
    do
    {
        let result = try context.fetch(request)
        if result.count > 0
        {
            let nameData = (result[0] as AnyObject).value(forKey: "name") as! String
            print(nameData)

        }
    }
    catch {
        //handle error
        print(error)
    }

    return cell
}

@IBAction func tap(_ sender: Any) {
    let url = "http://jsonplaceholder.typicode.com/users"
    var request = URLRequest(url: URL(string: url)!)
    request.httpMethod = "GET"
    let configuration = URLSessionConfiguration.default
    let session = URLSession(configuration: configuration, delegate: nil, delegateQueue: OperationQueue.main)
    let task = session.dataTask(with: request){(data, response,error)in
        if (error != nil){
            print("Error")
        }
        else{
            do{
                // Array of Data
                let fetchData = try JSONSerialization.jsonObject(with: data!, options: .mutableLeaves) as! NSArray

                for eachData in fetchData {

                    let eachdataitem = eachData as! [String : Any]
                    let name = eachdataitem["name"]as! String
                    let username = eachdataitem["username"]as! String

                    let email = eachdataitem["email"]as! String
                    self.displayDatasssss.append(displyDataClass(name: name, username: username,email : email))
                }
                self.tableView.reloadData()
            }
            catch{
                print("Error 2")
            }

        }
    }
    task.resume()

    }
}



class displyDataClass {
    var name : String
    var username : String
    var email : String

init(name : String,username : String,email :String) {
    self.name = name
    self.username = username
    self.email = email
   }
}

以下代码用于删除

// delete action two
        let deleteAction = UITableViewRowAction(style: .default, title: "Delete", handler: { (action, indexPath) in
            print("Delete tapped")

            // remove the deleted item from the model
            let appDel:AppDelegate = UIApplication.shared.delegate as! AppDelegate
            let managedObjectContext = appDel.persistentContainer.viewContext
            managedObjectContext.delete(self.displayDatasssssindexPath.row])
            self.milestoneTitles.remove(at: indexPath.row)
            do {
                try managedObjectContext.save()
            } catch _ {
            }

            self.tableView.deleteRows(at: [indexPath], with: .automatic)
           return [editAction, deleteAction]
       }

Answer 1

不要使用自定义类。仅使用提供的 User 类。

首先声明一个数据源数组（替换displayDatasssss）

var users = [User]()

在tap 方法中加载数据并在核心数据堆栈中插入新项目。考虑每次点击按钮都会将重复的项目插入数据库。旧条目不会被删除。

因为User 只有name 和id 属性，所以email 被分配给id。

项目被附加到数据源数组并保存在上下文中。

@IBAction func tap(_ sender: Any) {
    let url = "http://jsonplaceholder.typicode.com/users")!
    let task = session.dataTask(with: url){ [unowned self] (data, response,error)in
        if let error = error { print(error); return }
        do {
            // Array of Data
            let fetchData = try JSONSerialization.jsonObject(with: data!) as! [[String:Any]]    
            for eachDataItem in fetchData {                   
                let name = eachdataitem["name"] as! String
                let email = eachdataitem["email"] as! String
                let newUser = User(context: self.context)
                newUser.name = name
                newUser.id = email
                self.users.append(newUser)
            }
            DispatchQueue.main.async {
               self.tableView.reloadData()
            }
            try self.context.save()
       } catch{
           print("Error 2", error)
       }
    }
    task.resume()
}

在viewDidLoad 中从CoreData 获取数据并重新加载表格视图

override func viewDidLoad() {
    super.viewDidLoad()
    do {
       let request : NSFetchRequest<User> = User.fetchRequest()
       users = try context.fetch(request)
       tableView.reloadData()
    } catch { print(error) }
}

在cellForRow 中将属性值分配给标签，仅此而已

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "TableViewCell1") as! TableViewCell1 
    let user = users[indexPath.row]
    cell.label.text = user.name  
    return cell
}

delete方法和你的很像

let deleteAction = UITableViewRowAction(style: .default, title: "Delete", handler: { [unowned self] (action, indexPath) in
    print("Delete tapped")

    // remove the deleted item from the model
    let objectToDelete = self.users.remove(at: indexPath.row)
    self.context.delete(objectToDelete)
    do {
        try self.context.save()
        self.tableView.deleteRows(at: [indexPath], with: .automatic)
    } catch {
       print(error)
    }
}
return [editAction, deleteAction]

注意：总是打印错误，不要忽略它们或只打印无意义的文字字符串