使用核心數據來保存一個不斷變化的整數

Question

嗨，只是想知道這是否可能，我有一個簡單的計數器應用程序，每次按下按鈕時，計數器變量都會加1。當用戶使用核心數據退出應用程序時可以保存計數器嗎？我知道會NSUserDefaults的在這裏工作，但IM探索的核心數據，並想知道它是否能在情況下可以使用這樣

class ViewController: UIViewController { 

var counter = Int() 


@IBOutlet var label: UILabel! 

@IBAction func button(sender: AnyObject) { 
    counter += 1 
    label.text = "\(counter)" 



} 
override func viewDidLoad() { 
    super.viewDidLoad() 

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

NSManagedObject子類錯誤

class IntegerEntity: NSManagedObject { 


convenience init(entity: NSEntityDescription, insertIntoManagedObjectContext context: NSManagedObjectContext?, value: Int) { 
    self.init(entity: entity, insertIntoManagedObjectContext: context) 
    self.value 
    // ERROR value of type IntegerEntity has no member value 
} 
} 

ViewController.swift錯誤

import UIKit 
import CoreData 

class ViewController: UIViewController { 

var counter = Int() 


@IBOutlet var label: UILabel! 

@IBAction func button(sender: AnyObject) { 
    counter += 1 
    label.text = "\(counter)" 



} 
override func viewDidLoad() { 
    super.viewDidLoad() 

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

override func viewWillDisappear(animated: Bool) { 
    super.viewWillDisappear(animated) 

    let dataContext: NSManagedObjectContext! = (UIApplication.sharedApplication().delegate as? AppDelegate)?.managedObjectContext 
    var integerEntity: IntegerEntity! 
    if dataContext != nil { 
     let entity = NSEntityDescription.entityForName("IntegerEntity", inManagedObjectContext: dataContext) 
     let request = NSFetchRequest() 
     request.entity = entity 
     let integer = try? dataContext.executeFetchRequest(request) 

     if integer != nil && !integer!.isEmpty { 
      (integer?.first! as! IntegerEntity).value = counter 
      // ERROR value of type IntegerEntity has no member value 
     } else { 

      let newInt = IntegerEntity(entity: entity, insertIntoManagedObjectContext: context, value: counter) 
      // ERROR Use of unresolved identifier context 

      dataContext.saveData() 
     } 
    } 
} 

override func viewWillAppear(animated: Bool) { 
    super.viewWillAppear(animated) 
    let dataContext: NSManagedObjectContext! = (UIApplication.sharedApplication().delegate as? AppDelegate)?.managedObjectContext 
    var integerEntity: IntegerEntity! 
    if dataContext != nil { 
     let entity = NSEntityDescription.entityForName("IntegerEntity", inManagedObjectContext: dataContext) 
     let request = NSFetchRequest() 
     request.entity = entity 
     let integer = try? dataContext.executeFetchRequest(request) 

     if integer != nil && !integer!.isEmpty { 
      counter = (integer!.first! as! IntegerEntity).value 
      // ERROR value of type IntegerEntity has no member value 
     } else { 

      counter = 0 
     } 
    } 


} 

override func didReceiveMemoryWarning() { 
    super.didReceiveMemoryWarning() 
    // Dispose of any resources that can be recreated. 
} 


} 
extension NSManagedObjectContext { 
func saveData() -> Bool { 
    do { 
     try self.save() 
     return true 
    } catch let error as NSError { 
     print(error) 
     return false; 
    } 
} 
} 

Answer 1

這是可能的。

首先，創建一個核心數據模型並添加一個名爲IntegerEntity的實體。在實體中，添加名爲value的屬性，其類型爲Integer 64。現在生成NSManagedObject子類。

在IntegerEntity,swift，添加以下初始化：

convenience init(entity: NSEntityDescription, insertIntoManagedObjectContext context: NSManagedObjectContext?, value: Int) { 
    self.init(entity: entity, insertIntoManagedObjectContext: context) 
    self.value = value 
} 

這是因爲後面，我們可以用這個直接用一個價值創造的實體。

我想你的應用程序只有一個視圖控制器，所以你的時候，保存數據的兩個選項：

• 使用一個NSTimer保存數據每60秒或其他時間間隔
• 覆蓋視圖控制器中的viewDidDisappear或應用程序代理中的applicationWillResignActive。

要保存數據，首先需要獲取保存的整數（如果存在）。

// Just some boilerplate code here 
let dataContext: NSManagedObjectContext! = (UIApplication.sharedApplication().delegate as? AppDelegate)?.managedObjectContext 
var integerEntity: IntegerEntity! 
if dataContext != nil { 
    let entity = NSEntityDescription.entityForName("IntegerEntity", inManagedObjectContext: dataContext) 
    let request = NSFetchRequest() 
    request.entity = entity 
    let integer = try? dataContext.executeFetchRequest(request) 
    // If some integer has already been saved... 
    if integer != nil && !integer.isEmpty { 
     (integer?.first! as! IntegerEntity).value = counter 
    } else { 
     // If no integer has been saved before... 
     let newInt = IntegerEntity(entity: entity, insertIntoManagedObjectContext: context, value: counter) 
     dataContext.saveData() 
    } 
} 

您可能想知道，什麼是saveData？我認爲我的Xcode版本有一個錯誤。 Xcode始終堅持save()方法會拋出錯誤並返回Void。所以我創建了這個擴展：

extension NSManagedObjectContext { 
    func saveData() -> Bool { 
     do { 
      try self.save() 
      return true 
     } catch let error as NSError { 
      print(error) 
      return false; 
     } 
    } 
} 

和BOOM！而已！ 「

」但我該如何取回數據？你問。其實，你之前做過！代碼如下：

let dataContext: NSManagedObjectContext! = (UIApplication.sharedApplication().delegate as? AppDelegate)?.managedObjectContext 
    var integerEntity: IntegerEntity! 
    if dataContext != nil { 
     let entity = NSEntityDescription.entityForName("IntegerEntity", inManagedObjectContext: dataContext) 
     let request = NSFetchRequest() 
     request.entity = entity 
     let integer = try? dataContext.executeFetchRequest(request) 
     // If some integer has already been saved... 
     if integer != nil && !integer.isEmpty { 
      counter = (integer!.first! as! IntegerEntity).value.integerValue 
     } else { 
      // If no integer has been saved before... 
      counter = 0 
     } 
    } 

看起來很熟悉嗎？它幾乎和以前一樣！

警告

IMO，它不值得寫了這麼多代碼只是爲了救一個單獨的整數，只是讓你知道。改用用戶默認值。如果您想探索Core Data，可以嘗試在Core Data中保存單詞列表。然後按下一個按鈕，AVSpeechSynthesizer大聲朗讀。