删除CoreData对象

Question

哈哈，我仍在努力与CoreData开始一周。我终于成功保存并获取了我的数组，现在是时候编辑和删除了。

我首先添加了删除函数，但是我无法传递正确的参数：

核心数据功能：

class CDHandler: NSObject {

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

class func saveObject(name:String, code:String, symbol:String, placeholder:String, amount:String) -> Bool {
    let context = getContext()
    let entity = NSEntityDescription.entity(forEntityName: "CryptosMO", in: context)
    let managedObject = NSManagedObject(entity: entity!, insertInto: context)

    managedObject.setValue(name, forKey: "name")
    managedObject.setValue(code, forKey: "code")
    managedObject.setValue(symbol, forKey: "symbol")
    managedObject.setValue(placeholder, forKey: "placeholder")
    managedObject.setValue(amount, forKey: "amount")

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

class func fetchObject() -> [CryptosMO]? {
    let context = getContext()
    var cryptos: [CryptosMO]? = nil

    do {
        cryptos = try context.fetch(CryptosMO.fetchRequest()) as? [CryptosMO]
        return cryptos
    } catch {
        return cryptos
    }
}

class func deleteObject(crypto: CryptosMO) -> Bool {
    let context = getContext()
    context.delete(crypto)

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

}

创建和保存数组：

    if addedCrypto != "" {
        if addedCrypto == "Bitcoin BTC" {
            if CDHandler.saveObject(name: "Bitcoin", code: "bitcoin", symbol: "BTC", placeholder: "BTC Amount", amount: "0.0") {
                for crypto in CDHandler.fetchObject()! {
                    print("\(String(describing: crypto.name))'s symbol is \(String(describing: crypto.symbol))")
                }
            }
        }
    }

获取TableView的核心数据：

override func viewWillAppear(_ animated: Bool) {
    tableView.delegate = self
    tableView.dataSource = self


    if CDHandler.fetchObject() != nil {
        cryptos = CDHandler.fetchObject()!
        tableView.reloadData()
    }
}

TableView函数：

extension WalletTableViewController: UITableViewDelegate, UITableViewDataSource, CryptoCellDelegate {


func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return cryptos.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! WalletTableViewCell

    cell.cryptoNameLabel.text = cryptos[indexPath.row].name
    cell.amountTextField.placeholder = cryptos[indexPath.row].placeholder

    cell.delegate = self
    cell.amountTextField.delegate = self

    return cell
}
func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
    if editingStyle == .delete {
        cryptos.remove(at: indexPath.row)
        tableView.deleteRows(at: [indexPath], with: .fade)
        CDHandler.deleteObject(crypto: cryptos) // <----- Cannot convert value of type '[CryptosMO]' to expected argument type 'CryptosMO'
    }
}

}

这里有什么问题？我可以将func deleteObject(crypto: CryptosMO)改为func deleteObject(crypto: [CryptosMO])然后我得到Cannot convert value of type '[CryptosMO]' to expected argument type 'NSManagedObject'。

我读到delete()只把NSManagedObject作为唯一的参数，所以我相信我首先创建了一个不正确的对象，以便能够删除它？

Answer 1

只需调用此方法并使用要删除的managedObject传递实体：

func deleteData(entity:String,deleteObject:NSManagedObject){
    //for iOS 10+
           // let delegate = UIApplication.shared.delegate as? AppDelegate
           // let context = delegate!.persistentContainer.viewContext
            let context = getContext()
            context.delete(deleteObject)
            do {
                try context.save()
            } catch let error as NSError {
                print("Could not save. \(error), \(error.userInfo)")
            }

        }


 func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
        if editingStyle == .delete {
        let selectedManagedObject = cryptos[indexPath.row]
        deleteData(entity:"yourEntityName",deleteObject: selectedManagedObject)
            cryptos.remove(at: indexPath.row)
            tableView.deleteRows(at: [indexPath], with: .fade)
        }
    }

与您可以编辑的保存方法相同，只需要传递要编辑的managedObject：

class func updateObject(name:String, code:String, symbol:String, placeholder:String, amount:String,selectedManagedObject:NSManagedObject) {
    let context = getContext()

    selectedManagedObject.setValue(name, forKey: "name")
    selectedManagedObject.setValue(code, forKey: "code")
    selectedManagedObject.setValue(symbol, forKey: "symbol")
    selectedManagedObject.setValue(placeholder, forKey: "placeholder")
    selectedManagedObject.setValue(amount, forKey: "amount")

    do {
        try context.save()
    } catch let error as NSError {
        print("Could not save. \(error), \(error.userInfo)")
    }

}

Answer 2

当你打电话给CDHandler.deleteObject(crypto: ...)时，只需通过(crypto: cryptos[indexPath.row])而不是(crypto: cryptos)。

    ...
    CDHandler.deleteObject(crypto: cryptos[indexPath.row])
    cryptos.remove(at: indexPath.row)
    tableView.deleteRows(at: [indexPath], with: .fade)