将[String]存储在NSUserDefaults中 [英] Store [String] in NSUserDefaults

问题描述

我想将一个Swift样式字符串数组保存到NSUserDefaults中，但实际上代码中的if语句表示returnValue总是为零。

I want to save a Swift Style String Array into NSUserDefaults, but acutally the "if" statement in the code says that returnValue is always nil.

稍后在代码（iOS 8）我想用food + = [spaghetti]添加新条目。

Later in the code (iOS 8) I want to use "food += ["spaghetti"] to add new entries.

var food : [String] {
    get {
        var returnValue : [String]? = NSUserDefaults.standardUserDefaults().objectForKey("food") as? [String]
        if returnValue == nil      //Check for first run of app
        {
            returnValue = ["muesli", "banana"]; //Default value
        }
        return returnValue!
    }
    set (newValue) {
        NSUserDefaults.standardUserDefaults().setObject(newValue, forKey: "food")
        NSUserDefaults.standardUserDefaults().synchronize()
    }
}

推荐答案

以下代码可以帮助您解决问题：

The following code should help you resolve your problem:

import UIKit

class ViewController: UIViewController {

    var food: [String] {
        get {
            if let returnValue = NSUserDefaults.standardUserDefaults().objectForKey("food") as? [String] {
                return returnValue
            } else {
                return ["muesli", "banana"] //Default value
            }
        }
        set {
            NSUserDefaults.standardUserDefaults().setObject(newValue, forKey: "food")
            NSUserDefaults.standardUserDefaults().synchronize()
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        print(food) // prints: ["muesli", "banana"] (at first launch)

        food = ["cake"]
        print(food) // prints: ["cake"]

        food += ["spaghetti"]
        print(food) // prints: ["cake", "spaghetti"]

        food = []
        print(food) // prints: []

        NSUserDefaults.standardUserDefaults().setObject(nil, forKey: "food")
        print(food) // prints: ["muesli", "banana"]
    }

}

---

但是，使用前面的代码，如果你设置 food = [] ，你会遇到一个问题 food 将不会返回 [muesli，banana] 。为了避免这种情况，您可能更喜欢以下代码：

---

However, with the previous code, if you set food = [], you will have a problem as food won't return ["muesli", "banana"]. In order to avoid this, you may prefer the following code:

import UIKit

class ViewController: UIViewController {

    var food: [String] {
        get {
            if let returnValue = NSUserDefaults.standardUserDefaults().objectForKey("food") as? [String] {
                return returnValue == [] ? ["muesli", "banana"] : returnValue
            } else {
                return ["muesli", "banana"] //Default value
            }
        }
        set {
            NSUserDefaults.standardUserDefaults().setObject(newValue, forKey: "food")
            NSUserDefaults.standardUserDefaults().synchronize()
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        print(food) // prints: ["muesli", "banana"] (at first launch)

        food = ["cake"]
        print(food) // prints: ["cake"]

        food += ["spaghetti"]
        print(food) // prints: ["cake", "spaghetti"]

        food = []
        print(food) // prints: ["muesli", "banana"]

        NSUserDefaults.standardUserDefaults().setObject(nil, forKey: "food")
        print(food) // prints: ["muesli", "banana"]
    }

}

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