对于Swift中的NSUserDefaults，objectForKey返回nil

Question

我使用以下代码使用Swift将值设置为NSUserDefaults。这是我的代码：

let key = "ticker"
let currencyTickerData = [key:"USD"]
NSUserDefaults.standardUserDefaults().setObject(currencyTickerData, forKey: key)
NSUserDefaults.standardUserDefaults().synchronize()

let tickerVal : [NSString]? = (NSUserDefaults.standardUserDefaults().objectForKey(key)) as? [NSString]

print(tickerVal)

出于某种原因，tickerVal为零。为什么是这样？据我所知，它应该返回“USD。”

Answer 1

NSUserDefaults使用NSDictionary而不是Swift的字典类型。您可以显式键入tickerVal作为NSDictionary，如下所示：

let key = "ticker"
let currencyTickerData: NSDictionary = [key:"USD"]
NSUserDefaults.standardUserDefaults().setObject(currencyTickerData, forKey: key)
NSUserDefaults.standardUserDefaults().synchronize()

let tickerVal = (NSUserDefaults.standardUserDefaults().objectForKey(key)) as NSDictionary

print("\(tickerVal)")

Answer 2

与您保存日期的代码相同：

var myValue:NSString = "USD"

NSUserDefaults.standardUserDefaults().setObject(myValue, forKey:"ticker")
NSUserDefaults.standardUserDefaults().synchronize()

var myOutput: AnyObject? = NSUserDefaults.standardUserDefaults().objectForKey("ticker")
println(myOutput)