我想把一个Swift样式字符串数组保存到NSUserDefaults,但是在代码中的“if”语句表示returnValue总是nil。
后来在代码中我想使用“food = [”spaghetti“]来添加新条目。
- 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()
- }
- }
以下代码可以帮助您解决问题:
- 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"]
- }
- }
然而,使用上面的代码,如果你设置food = [],你会有一个问题,因为食物不会返回[“muesli”,“banana”]。为了避免这种情况,你可能更喜欢下面的代码:
- 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","spaghetti"]
- food = []
- print(food) // prints: ["muesli","banana"]
- NSUserDefaults.standardUserDefaults().setObject(nil,"banana"]
- }
- }