Swift中的错误投射问题

Question

Not sure if this a bug or an intended feature.

To create a user with an email and password in Firebase, I've been using the following code:

FIRAuth.auth()?.signIn(withEmail: email, password: password) { (user, error) in
    if let error = error {
        guard let error = error as? FIRAuthErrorCode else { return } // ALWAYS FAILS 
        ...code...
    }
    ...code...
}

The error parameter in the completion handler for the method cannot be cast as FIRAuthErrorCode ; it always fails. Is that a bug, or is that the expected behaviour?

Edit: I am aware that error codes can be used to distinguish between the different types of FIRAuthErrorCode errors. It's just not readable, and it doesn't make much sense for the error parameter in the completion handler to be not of be of type FIRAuthErrorCode . The cases and error codes of FIRAuthErrorCode can be found here .

Answer 1

Have you tried using guard let error = error as! FIRAuthErrorCode else { return } guard let error = error as! FIRAuthErrorCode else { return } to force the casting and check whether the return is nil or not?

Answer 2

您应检查firebase中signIn方法的文档，以检查此方法可以发送的所有可能的错误类型，然后在代码中的保护块中检查这些类型的错误。

Answer 3

Try this, it's how I do my login and it seems to work great.

FIRAuth.auth()?.signIn(withEmail: EmailField.text!, password: PasswordField.text!, completion: { user, error in
        if error == nil {
        print("Successfully Logged IN \(user!)")
        self.performSegue(withIdentifier: "Login", sender: self)
        }
    })

I just check that there's not an error with the signin process, then perform my segue.

Answer 4

After contacting Firebase support about the issue, they've said that the errors that are passed back in completion handlers are just Error objects. They weren't FIRAuthErrorCode objects. To test for the various FIRAuthErrorCode cases, one would have to do something like this:

FIRAuth.auth()?.signIn(withEmail: email, password: password) { (user, error) in
    if let error = error {
        guard let error = FIRAuthErrorCode(rawValue: error._code) else {
            fatalError("This should never be executed")
        }
        switch error {
        case .errorCodeInvalidEmail: ...
        case .errorCodeWrongPassword: ...
        default: ...

        }
        ...code...
    }
    ...code...
}

^ This preserves readability and makes error handling more intuitive. And, there is no need for error casting!