使用 Swift 检索核心数据

Question

问题

我是 IOS 开发的新手，一直在努力使用 Core Data。我正在尝试使用开关创建设置页面。我需要记住这个开关是打开还是关闭。我创建了一个核心数据应用程序，并设法弄清楚如何将开关的值保存到属性中。下面的代码做到了这一点，我只是不知道如何将开关的保存值恢复为打开或关闭。我该怎么做？谢谢！

核心数据图片

代码：

import UIKit
import CoreData
class preferencesStuff: UIViewController {

override func viewDidLoad() {
    super.viewDidLoad()

    var appDel:AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)
    var context:NSManagedObjectContext = appDel.managedObjectContext!

    var request = NSFetchRequest(entityName: "Settings")
    request.returnsObjectsAsFaults = false;
    var results:NSArray = context.executeFetchRequest(request, error: nil)!

    if(results.count > 0){
        if results[results.count-1] as NSObject == 1 {
            println("ON")
        }


    }else{
        println("NO RESULTS")
    }

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}
@IBOutlet weak var fractSwitchValue: UISwitch!

@IBAction func fractSwitch(sender: AnyObject) {
    if fractSwitchValue.on == true {
        var appDel:AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)
        var context:NSManagedObjectContext = appDel.managedObjectContext!

        var newSetting = NSEntityDescription.insertNewObjectForEntityForName("Settings", inManagedObjectContext: context) as NSManagedObject
        newSetting.setValue(true, forKey: "fractionOnOff")

        context.save(nil)
        //println(newSetting)


    }
    else {
        var appDel:AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)
        var context:NSManagedObjectContext = appDel.managedObjectContext!

        var newSetting = NSEntityDescription.insertNewObjectForEntityForName("Settings", inManagedObjectContext: context) as NSManagedObject
        newSetting.setValue(false, forKey: "fractionOnOff")

        context.save(nil)
        //println(newSetting)

    }
}

}

Answer 1

我刚刚用 CoreData 做了你的例子。我只是碰巧存储了一个 NSString 而不是 Bool。它没有经过优化，但它应该能让你继续前进。

import UIKit
import CoreData

class ViewController: UIViewController {

    var state: NSString = ""

    @IBOutlet weak var fractSwitchValue: UISwitch!

    @IBAction func fractSwitch(sender: AnyObject) {
        if fractSwitchValue.on == true {
            state = "On"
            save(state)
        }
        else {
            state = "Off"
            save(state)
        }
    }

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

        var appDel = UIApplication.sharedApplication().delegate as AppDelegate
        var context = appDel.managedObjectContext!
        var request = NSFetchRequest(entityName: "Settings")
        var error: NSError?
        var results = context.executeFetchRequest(request, error: &error) as [NSManagedObject]?

        if let fetchedResults = results {
            state = fetchedResults[fetchedResults.count - 1].valueForKey("fractionOnOff") as String!
        } else {
            println("Could not fetch \(error), \(error!.userInfo)")
        }

        if state == "On" {
            fractSwitchValue.setOn(true, animated: true)
        }  else {
            fractSwitchValue.setOn(false, animated: true)
        }
    }

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

    func save(string: NSString) {
        let appDel = UIApplication.sharedApplication().delegate as AppDelegate
        let context = appDel.managedObjectContext!
        let entity =  NSEntityDescription.entityForName("Settings", inManagedObjectContext: context)
        let setting = NSManagedObject(entity: entity!, insertIntoManagedObjectContext: context)
        setting.setValue(string, forKey: "fractionOnOff")
        println(string)
        var error: NSError?
        if !context.save(&error) {
            println("Could not save \(error), \(error?.userInfo)")
        }
    }
}

Answer 2

我会在这种情况下使用NSUserDefaults。在存储用户偏好时，它比 Core Data 更容易使用。例如，您可以使用

来存储属性

NSUserDefaults.standardUserDefaults().setBool(value, forKey: "fractionPreference")

并使用检索它

let value = NSUserDefaults.standardUserDefaults().boolForKey("fractionPreference")