Daniel Que Daniel Que - 26 days ago 35x
iOS Question

Alamofire 'invalid type in JSON write' error after upgrading

The following code was working with Alamofire 3.0:

let headers = [
"content-type": "application/json",
"cache-control": "no-cache",
let parameters = [
"access_token": token.tokenString,
"client_id": bundleID,

Alamofire.request(.POST, url, headers: headers, parameters: parameters, encoding: .JSON).responseJSON { response in
// ...

I changed the request after updating to Alamofire 4.0/Swift3/XCode 8:

Alamofire.request(url, method: .post, parameters: parameters, encoding: JSONEncoding.default, headers: headers).responseJSON { response in
// ...

And I get the error

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Invalid type in JSON write (_SwiftValue)'

I've been looking for a solution to this problem but can't find anything relevant.


There is definitely something wrong with your parameters. Make sure that both token.tokenString and bundleID are Strings.