Max Max - 1 year ago 523
iOS Question

completion handler's error in swift 3 and Xcode 8

I have working project in Xcode 7.3 with swift 2.2 version. Now I have updated Xcode 8 and migrated to swift 3. Now my project contains errors specially for blocks like success block of afnetworking.

Snapshot for error in afnetworking post method

Which gives error as

Cannot convert value of type '() -> ()' to expected argument type '((URLSessionDataTask, Any?) -> Void)?'

I don't understand how to solve this to work as per swift 3.

And there is also same like error in Facebook login.

Facebook Login error

Which gives error as

Cannot convert value of type '(FBSDKLoginManagerLoginResult!, NSError!) -> Void' to expected argument type 'FBSDKLoginManagerRequestTokenHandler!'


Cannot convert value of type '(_, _, NSError!) -> Void' to expected argument type 'FBSDKGraphRequestHandler!'

This all errors are related to handler blocks in swift 3. I don't understand the errors and so that can't able to solve. Any help will be appreciated. Thanks in advance.

Max Max
Answer Source

Though I didn't know the error before that what Xcode want to inform me about the error, but I have removed type specification with object and it worked.

As, parameters: param, progress: nil, success:{ (dataTask, responseObj) in

                if let dict : NSDictionary = responseObj as? NSDictionary {

                    print("Response of \(methodname) : \(dict)")

                    if dict.object(forKey: "response") as? String == "success" {
                        CompletionHandler(true, dict)
                    } else {
                        CompletionHandler(false, dict)



Here with respect to question error is given at dataTask and responseObj which are with type specified. After removing type it worked fine.

Same as with facebook login

@IBAction func fbLoginClicked(_ sender: AnyObject) {

        let app = UIApplication.shared.delegate as! AppDelegate

        app.fbLoginManager = FBSDKLoginManager()
        app.fbLoginManager.loginBehavior = FBSDKLoginBehavior.native

        app.fbLoginManager.logIn(withReadPermissions: ["email"], from: self, handler: { (result, error) -> Void in
            if error != nil {
            } else {

                if (result! as FBSDKLoginManagerLoginResult).isCancelled == true {

                } else {



Here also I have removed type specification of result and error and problem solved. And followed this in whole app and it worked. I can run the project without error and also it is working. Thanks.

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