class ActivityA: AppCompatActivity() {

    companion object {
        private const val SOME_CODE = 1
    }

    private fun someAction() {
        ActivityB.startForResult(this, "some param", SOME_CODE)
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        if (requestCode == SOME_CODE) {
            if(resultCode == Activity.RESULT_OK) {
                //to do something
            }
        }
    }
}
class ActivityB: AppCompatActivity() {

    companion object {
        private const val PARAM_KEY = "PARAM_KEY"
        fun startForResult(activity: Activity, param: String, code: Int) {
            val intent = Intent(activity, ActivityB::class.java).apply {
                putExtra(PARAM_KEY, param)
            }
            activity.startActivityForResult(intent, code)
        }
    }

    private var param = ""

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        intent?.apply {
            param = getStringExtra(PARAM_KEY)
        }
    }

    fun someAction() {
        setResult(Activity.RESULT_OK)
        finish()
    }

}