Try! throwing fatal error in Swift 3, issues updating from Swift 2 - swift3

Question

I am trying to parse the JSON data from my server and I am getting an error when it hits the try! statement and it is crashing. It is telling me
Code=3840 "Invalid value around character 0.
It my be because I have not updated my code correctly to Swift 3. I was having an issue with if let parse for the longest time until I switched the as to as?
#IBAction func registerButtonTapped(_ sender: Any) {
let userEmail = userEmailTextField.text;
let userPassword = userPasswordTextField.text;
let userRepeatPassword = repeatPasswordTextField.text;
// Check for empty fields
if((userEmail?.isEmpty)! || (userPassword?.isEmpty)! || (userRepeatPassword?.isEmpty)!){
//Display alert message
displayMyAlertMessage(userMessage: "All fields are required");
return;
}
//Check if passwords matech
if(userPassword != userRepeatPassword){
// Display alert message
displayMyAlertMessage(userMessage: "Passwords do not match");
return;
}
// Send user data to server side
let myUrl = URL(string: "http://");
let request = NSMutableURLRequest(url:myUrl!);
request.httpMethod = "Post";
let postString = "email=\(userEmail)&password=\(userPassword)";
//adding the parameters to request body
request.httpBody = postString.data(using: String.Encoding.utf8);
//creating a task to send the post request
let task = URLSession.shared.dataTask(with: request as URLRequest){
data, response, error in
if error != nil{
print("error=\(error)")
return
}
//parsing the reponse
//converting response to Any
let json = try! JSONSerialization.jsonObject(with: data!, options: JSONSerialization.ReadingOptions.allowFragments) as? [String:Any]
//parsing JSON
if let parseJSON = json{
let resultValue = parseJSON["status"] as? String
print("result: \resultValue)")
var isUserRegistered:Bool = false;
if(resultValue=="Success") { isUserRegistered = true;}
var messageToDisplay:String = parseJSON["messsage"] as! String;
if(!isUserRegistered)
{
messageToDisplay = parseJSON["message"] as! String;
}
DispatchQueue.main.async {
//Display alert message with confirmation.
let myAlert = UIAlertController(title:"Alert", message:messageToDisplay, preferredStyle: UIAlertControllerStyle.alert);
let okAction = UIAlertAction(title:"ok", style:UIAlertActionStyle.default){ action in
self.dismiss(animated: true, completion:nil);
}
myAlert.addAction(okAction);
self.present(myAlert, animated:true, completion:nil);
};
}
}
task.resume()
}
Please help, thanks

Answer 1

The reason of the error is that you are sending literal "Optional(Foo)" strings to the server via String Interpolation. userEmail and userPassword will never match and the server sends no data back. In Swift 3 you have to explicitly unwrap even implicit unwrapped optional strings.
The solution is a waterproof error handling with optional bindings
#IBAction func registerButtonTapped(_ sender: AnyObject) {
// Check for empty fields
guard let userEmail = userEmailTextField.text, !userEmail.isEmpty,
let userPassword = userPasswordTextField.text, !userPassword.isEmpty,
let userRepeatPassword = repeatPasswordTextField.text, !userRepeatPassword.isEmpty else {
//Display alert message
displayMyAlertMessage(userMessage: "All fields are required")
return
}
...
Now all relevant optionals are safely unwrapped and the server will get the right data.
Further trailing semicolons and parentheses around if conditions are not needed in Swift and use URLRequest rather than NSMutableURLRequest in Swift 3
var request = URLRequest(url:myUrl!) // var is mandatory if properties are going to be changed.
PS: In any case – as already mentioned in the comments – never use carelessly try! when receiving data from a server.