如何将Swift字典转换为NSDictionary

Question

我正在尝试将[String : String]（Swift字典）转换为NSDictionary，以供以后在产生字符串的JSON库上使用

var parcelDict = ["trackingNumber" : parcel.number,
                  "dstCountry" : parcel.countryCode];

if (parcel.postalService != nil) 
{
    parcelDict["postalService"] = parcel.postalService;
}

var errorPtr: NSErrorPointer
let dict: NSDictionary = parcelDict
var data = NSJSONSerialization.dataWithJSONObject(dict, options:0, error: errorPtr) as NSData

return NSString(data: data, encoding: NSUTF8StringEncoding)

但let dict: NSDictionary = parcelDict不起作用

let dict: NSDictionary = parcelDict as NSDictionary

var data = NSJSONSerialization.dataWithJSONObject(parcelDict as NSMutableDictionary, options:0, error: errorPtr) as NSData

所有这些示例都不起作用。它们产生以下错误：

正确的做法是什么？

更新：

有效的代码

var parcelDict = ["trackingNumber" : parcel.number!,
                  "dstCountry" : parcel.countryCode!];

if (parcel.postalService != nil) {
    parcelDict["postalService"] = parcel.postalService;
}

var jsonError : NSError?
let dict = parcelDict as NSDictionary
var data = NSJSONSerialization.dataWithJSONObject(dict, options:nil, error: &jsonError)
return NSString(data: data!, encoding: NSUTF8StringEncoding)!

Answer 1

您必须像这样强制转换：

let dict = parcelDict as NSDictionary

否则，在ex的方法中使用Swift字典和NSDictionary时，其处理方式几乎相同：

func test(dict: NSDictionary) {}

let dict = ["Test":1]
test(dict)

将完全正常工作。

更新后

如果将Dictionary值类型更改为非可选的String，则错误将消失。

[String:String?] change to -> [String:String]