Open a new view controller after login alert swift 2.0 - swift

Question

I am trying to change view controller if the login is successful but I am unsure how to do this. This is what i have tried so far. Thanks in advance!
#IBAction func signinaction(sender: AnyObject) {
let user = self.usernamefield.text!
ref.authUser(emailfield.text, password: passwordfield.text, withCompletionBlock: { error, authData in
if error != nil
{
let alert = UIAlertController(title: "Error", message: "Enter Email and Password.", preferredStyle: UIAlertControllerStyle.Alert)
let action = UIAlertAction(title: "Ok", style: .Default, handler: nil)
alert.addAction(action)
self.presentViewController(alert, animated: true, completion: nil)
print("can not sign in")
}
else
{
let storyboard = UIStoryboard(name: "Main", bundle: nil);
let viewName:NSString = "NewView"
let vc = storyboard.instantiateViewControllerWithIdentifier(viewName as String) as! HomeViewController
let uid = authData.uid
print("Success with user: \(uid)")
let alert = UIAlertController(title: "Success", message: "Welcome \(user)", preferredStyle: UIAlertControllerStyle.Alert)
let action = UIAlertAction(title: "Ok", style: .Default, handler: nil)
alert.addAction(action)
self.navigationController?.pushViewController(vc as HomeViewController, animated: true)
}
})
}

Answer 1

Assuming that the view controller all of this is in is contained in a navigation controller, what you have should be working fine. Note, however that you're creating an alert you never show. My guess is that you want to display the success alert and then open the new view controller, something like:
let alert = UIAlertController(title: "Success", message: "Welcome \(user)", preferredStyle: UIAlertControllerStyle.Alert)
let action = UIAlertAction(title: "Ok", style: .Default) { _ in
self.navigationController?.pushViewController(vc, animated: true)
}
alert.addAction(action)
self.presentViewController(alert, animated: true, completion: nil)
If this still isn't working, I'd make sure the current view controller is actually displayed in a navigation controller.

Answer 2

Looks like you just need to add the navigation code inside of the alert action. Currently you have the handler parameter set to nil
this
let action = UIAlertAction(title: "Ok", style: .Default, handler: nil)
becomes this
let alertAction = UIAlertAction(title: "Ok", style: .Default) { (action) -> Void in
self.navigationController?.pushViewController(vc as HomeViewController, animated: true)
}