[iOS] Could not cast value of type ‘__NSCFNumber’ to ‘NSString’

json 長醬子：

{
"base": "EUR",
"date": "2017-05-16",
"rates": {
    "AUD": 1.492,
}}

直接用 String 去存取  “AUD” 欄位，會出錯，解法是用 Float 或Double去接浮點數，如果需要轉成 String 就用 String 包起來：

if let rateDict = dict["rates"] as? [String : Any] {
    if let aud = rateDict["AUD"] as? Float {
        print("\(aud)")
    }
}

You can convert it in string like,

let aud : String = String(rateDict["AUD"])