Using Parse SDK with swift , PFUser.currentUser().fetch() not working - swift

Question

After a user has logged in and if they later decide they want to change their username they have the ability to do so. when I save the record I catch the parse errors for username already exists and email already exists.
The issue I have is if the user decides not change their info after that the app is keeping the "BAD Username" in the cache and shows it all over the app.
I have tried calling PFUser.currentUser().fetch() as you will see below to refresh it from what is in the DB but to no avail.
The only thing that works is signing out and back in to get it back to whats in the DB.
Any ideas?
heres my code to catch the username error and attempt to refresh the PFUser
func saveUser() {
let username = nameField.text
let firstname = firstNameField.text! as String
let lastname = lastNameField.text! as String
let profilemsg = profileMessage.text! as String
let email = emailField.text! as String
if username!.characters.count > 0 {
let user = PFUser.currentUser()
if let user = user {
user["username"] = username
user["first"] = firstname
user["last"] = lastname
user["greeting"] = profilemsg
user["email"] = email
}
user!.saveInBackgroundWithBlock {(success: Bool, error: NSError?) -> Void in
if (success) {
ProgressHUD.showSuccess("Saved")
} else {
let errorCode = error!.code
switch errorCode {
case 202:
ProgressHUD.showError("Username " + username! + " already taken")
self.nameField.text = nil
do
{
try PFUser.currentUser()!.fetch()
print("User refreshed")
}
catch{
}
break
case 203:
ProgressHUD.showError("E-mail " + email + " already taken")
self.emailField.text = nil
do
{
try PFUser.currentUser()!.fetch()
print("User refreshed")
}
catch{
}
break
default:
ProgressHUD.showError("Network Error")
break
}
}
}
} else {
ProgressHUD.showError("Userame field must not be empty")
}
}

Answer 1

There is no need on creating a new instance of user to save the currentUser.
Just make the changes on the currentUser as it follows:
PFUser.currentUser()!["username"] = username
...
and then save it:
PFUser.currentUser()!.saveInBackgroundWithBlock {(...)}