UnityGameActivity.kt

class UnityGameActivity : UnityPlayerActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        mUnityPlayer += MaterialButton(this).apply {
            ...
            text = "RANDOMIZE COLOR"

            setOnClickListener {
                val color = listOf("blue", "green", "red", "yellow").random()
                UnityPlayer.UnitySendMessage("Capsule", "ChangeColor", color)
            }
        }

        mUnityPlayer += MaterialButton(this).apply {
            ...
            text = "QUIT"

            setOnClickListener {
                val intent = Intent(context, MainActivity::class.java).apply {
                    flags = Intent.FLAG_ACTIVITY_REORDER_TO_FRONT or Intent.FLAG_ACTIVITY_SINGLE_TOP
                }
                startActivity(intent)
            }
        }

        mUnityPlayer += JoystickView(this).apply {
            ...

            findViewById<View>(R.id.forward).setOnClickListener {
                UnityPlayer.UnitySendMessage("Capsule", "MoveUp", "")
            }
            ...
        }
    }
}