Android Alert Dialog with custom layout

The following code will display an Android Alert Dialog with a custom layout. When the login button is clicked, the dialog will show up in the center of the screen. The dialog will have a title, and two EditText for email and password, alone with cancel and submit buttons.

MainActivity.kt

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.support.v7.app.AlertDialog
import android.view.LayoutInflater
import android.view.View
import android.widget.EditText
import android.widget.Toast

class MainActivity : AppCompatActivity() {

    private var etEmail: EditText? = null
    private var etPassword: EditText? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    fun login(view : View) {
        // Inflates the dialog with custom view
        val dialogView = LayoutInflater.from(this).inflate(R.layout.login_dialog, null)

        etEmail = dialogView.findViewById(R.id.et_email)
        etPassword = dialogView.findViewById(R.id.et_password)
        var title = "Login"

        val builder = AlertDialog.Builder(this)
                .setView(dialogView)
                .setTitle(title)
                .setPositiveButton("Submit", null)
                .setNegativeButton("Cancel", null)
        val dialog = builder.show()
        dialog.getButton(AlertDialog.BUTTON_POSITIVE).setOnClickListener({
                    dialog.dismiss()
                    Toast.makeText(applicationContext, "Login is submitted, verify the credential and log the user into the app", Toast.LENGTH_SHORT).show()
                }
        )
    }
}

activity_main.xml

login_dialog.xml