Unrecognised selector sent to instance causing app crash

I lack information to be sure, but if handleCustomSignIn has a parameter, you should tell it to selector :

Selector(("handleCustomSignIn:"))

Nota: syntax for selector should be better with :

#selector(handleCustomSignIn(_:)) or #selector(handleCustomSignIn(param:)) if the parameter has a name

My selectors don't need any parameters as they are only meant to move to the next view controller.

I have other selectors and they all work except for this one

Seeing your code, you have added two targets for the same object `customSignInProviderButton` and the same event `.touchUpInside`.

So, your VC needs to have two methods:

    @objc func handleCustomSignIn() {
        //...
    }

And:

    @objc func UserLogIn() {
        //...
    }

Any of the two `customSignInProviderButton.addTarget(self, ...)` may be a mistake, but to make your current code work, both methods needed.

And as already noted, both methods cannot have any parameters.

By the way, in Swift 3, you'd better use `#selector` notation (like in your `doneButton` declaration), rather than using initializer of `Selector`.

When you use an unimplemented method in a `#selector` notation, Xcode or Swift will tell you that while editing, or at least compiletime.

I have tried redeclaring my functions as the following:

@objc func handleCustomSignIn() {
     //...
}

But still nothing has changed.

Where is `UserLogIn` ? You'd better show whole your VC, which can reproduce the issue. Without showing all we need, a long guess game would go on...

Righto then here is the entire View Controller.

import UIKit
import AWSMobileHubHelper
import FBSDKCoreKit
import FBSDKLoginKit
class SignInViewController: UIViewController {
   
        var didSignInObserver: AnyObject!
        var passwordAuthenticationCompletion: AWSTaskCompletionSource<AnyObject>?
   
    @IBOutlet weak var customUserIdField: UITextField!
    @IBOutlet weak var customPasswordField: UITextField!
    @IBOutlet weak var customCreateNewAccountButton: UIButton!
    @IBOutlet weak var customForgotUserPassword: UIButton!
    @IBOutlet weak var customSignInProviderButton: UIButton!
    @IBOutlet weak var facebookLoginButton: FBSDKLoginButton!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        print("Sign in loading")
       
        didSignInObserver =  NotificationCenter.default.addObserver(forName: NSNotification.Name.AWSIdentityManagerDidSignIn,
        object: AWSIdentityManager.defaultIdentityManager(),
        queue: OperationQueue.main,
        using: {(note: Notification) -> Void in
        customSignInProviderButton.addTarget(self, action: Selector(("handleCustomSignIn")), for: .touchUpInside)
        customCreateNewAccountButton.addTarget(self, action: Selector(("handleUserPoolSignUp")), for: .touchUpInside)
        customForgotUserPassword.addTarget(self, action: Selector(("handleUserPoolForgotPassword")), for: .touchUpInside)
        customSignInProviderButton.addTarget(self, action: Selector(("UserLogIn")), for: .touchUpInside)
       
        let toolBar = UIToolbar()
        toolBar.sizeToFit()
        let flexibleSpace = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.flexibleSpace, target: nil, action: nil)
        let doneButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.done, target: self, action: #selector(self.doneClicked))
        toolBar.setItems([flexibleSpace, doneButton], animated: false)
        customUserIdField.inputAccessoryView = toolBar
        customPasswordField.inputAccessoryView = toolBar
    }
   
    deinit {
        NotificationCenter.default.removeObserver(didSignInObserver)
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
   
    func handleFacebookLogin() {

        AWSFacebookSignInProvider.sharedInstance().setPermissions(["public_profile"]);
        handleLoginWithSignInProvider(signInProvider: AWSFacebookSignInProvider.sharedInstance())
    }


    func handleLoginWithSignInProvider(signInProvider: AWSSignInProvider) {
        Before Editing
        AWSIdentityManager.defaultIdentityManager().loginWithSign(signInProvider, completionHandler:
            {(result, error) -> Void in
                if error == nil {
                    
                    DispatchQueue.main.async(execute: {
                        self.presentingViewController?.dismiss(animated: true, completion: nil)
                    })
                }
                print("Login with signin provider result = \(result), error = \(error)")
        }
       
        AWSIdentityManager.defaultIdentityManager().loginWithSign(signInProvider, completionHandler: {(result, error) -> Void in
            if error == nil {
              
                DispatchQueue.main.async(execute: {
                    self.presentingViewController?.dismiss(animated: true, completion: nil)
                })
            }
            print("Login with sign in provider result = \(result), error =\(error)")
        })
    }
   

    func dismissViewController() {
        self.dismiss(animated: true, completion: nil)
    }
   

    func doneClicked() {
        view.endEditing(true)
    }
}

As I wrote, your `SignInViewController` does not have a method named `UserLogIn`, but you have this line:

customSignInProviderButton.addTarget(self, action: Selector(("UserLogIn")), for: .touchUpInside)

So, when `customSignInProviderButton` is tapped, iOS searches a method named `UserLogIn` inside `self` which is a `SignInViewController`.

But your `SignInViewController` dose not have a method named `UserLogIn`, so iOS terminates with saying 'unrecognised selector sent to instance.'

Remove that line and check what you can find without that line.

And one more.

Your `SignInViewController` does not have methods named `handleUserPoolSignUp` or `handleUserPoolForgotPassword`. That would never work.

But you said they all work except for this one.

Say only truth if you really want to fix your issue.

I was using a template from aws mobile hub and the selectors are used to initialize the buttons.

So how do these work then?

    loginButton.addTarget(self, action: "handleCustomSignIn", forControlEvents: .TouchUpInside)
    createAccountButton.addTarget(self, action: "handleUserPoolSignUp", forControlEvents: .TouchUpInside)
    forgotPassword.addTarget(self, action: "handleUserPoolForgotPassword", forControlEvents: .TouchUpInside)

Your code is completely broken. You have said you have redeclared your function as `@objc func handleCustomSignIn() {...}`, but there's no method named `handleCustomSignIn` in your code.

When you write `addTarget`, you need to implement all methods specified in `selector: ...`.

Update your code implementing all the action methods you need and come again with your updated code.