Return Boolean from Block in Swift

Question

I am trying to use Parse written with Swift. I am able to log in without any trouble but I am struggling with telling my app that the user is logged in.

I am using logInWithUsernameInBackground and I simply want to return a boolean if the log in succeeded.

When I use:

func authenticateUser() -> Bool{
    PFUser.logInWithUsernameInBackground(userName.text, password: passwordField.text, block: {
        (user,error) in
        return error === nil
    })
}

I get the error "Bool is not convertible to Void" which makes sense.

So if I change line 3 to read:

(user,error) -> Bool in

I end up with the error "Missing argument for parameter selector in call"

However, This method doesn't require a selector parameter.

So where am I going wrong? How do I return a bool based on whether or not there was an error at log in?

Answer 1

Based on the code as you wrote it, if you wanted to return Bool, you'd do this:

func authenticateUser() -> Bool{
    PFUser.logInWithUsernameInBackground(userName.text, password: passwordField.text, block: {
        (user,error) in
        return error === nil
    })

    return true // This is where the bool is returned
}

However, what you want to do, based on your code, is:

func authenticateUser(completion:(Bool) -> ()) {
    PFUser.logInWithUsernameInBackground(userName.text, password: passwordField.text, block: {
        (user,error) in
        completion(error === nil)
    })
}

You can invoke the call by one of the following:

authenticateUser(){
    result in
    if result {
        println("Authenticated")
    } else {
        println("Not authenticated")
    }
}

or

authenticateUser({
  result in
    if result {
        println("Authenticated")
    } else {
        println("Not authenticated")
    }
})

The first one is shorthand and is more convenient when you have other arguments prior to the closure.

This implies that you are getting back your Bool for as to whether or not you authenticated asynchronously.

BTW, you really only need to do error == nil