LoginActivity

class LoginActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_login)
        supportActionBar?.hide()

        btn_login.setOnClickListener {
            login()
        }
    }

    fun login() {

        var username = text_username.text.toString()
        var password = text_password.text.toString()

        if(username == "admin" && password == "admin"){

            var intent = Intent(this, ListActivity::class.java)
            startActivity(intent)
        } else {

            Toast.makeText(this, "This is a message displayed in a Toast", Toast.LENGTH_SHORT).show();

        }
    }
}