How do I convert swift Dictionary to NSDictionary - ios

Question

I'm trying to convert a [String : String] (a Swift Dictionary) to NSDictionary, for later use on a JSON library that produces a string
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)
but let dict: NSDictionary = parcelDict does not work
let dict: NSDictionary = parcelDict as NSDictionary
var data = NSJSONSerialization.dataWithJSONObject(parcelDict as NSMutableDictionary, options:0, error: errorPtr) as NSData
All of these examples do not work. They produce the following errors:
What's the correct way of doing it?
Update:
Code that works
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

You have to cast it like this:
let dict = parcelDict as NSDictionary
Otherwise the Swift Dictionary and NSDictionary are treated almost the same way when using it in methods for ex:
func test(dict: NSDictionary) {}
let dict = ["Test":1]
test(dict)
Will work completely fine.
After your update
If you change your Dictionary value type to non optional String then your error will go away.
[String:String?] change to -> [String:String]

Answer 2

You can use this easy method
let dictSwift = ["key1": "value1", "key1": value2]
let dictNSMutable = NSMutableDictionary(dictionary: dictSwift)
Enjoy coding!

Answer 3

Don't don't need to convert it to an NSDictionary. Just use:
var data = NSJSONSerialization.dataWithJSONObject(parcelDict, options:0, error: errorPtr) as NSData
It's mentioned in this post: Making a JSON object in Swift
Edit
From your screenshots I believe your problem lies in the value type in your parcelDict Dictionary. I can recreate the error with the following code:
let dict = [String: String?]()
let nsDict = dict as NSDictionary // [String: String?] is not convertible to NSDictionary
However, using a String instead of a String? as the value type removes the error.
Therefore, when populating parcelDict perhaps you should only add to it values which are not nil.