How to solve error with calling kotlin activity method from java singleton?

Andrew :

I would like to call this method:

fun workingWithBtn(k: Int) {
        when (k) {
            1 -> {
                btn_submit_t.showError();
                Handler().postDelayed({
                    [email protected] {
                        btn_submit_t.hideLoading()
                        btn_submit_t.isEnabled
                    }
                }, 1000)
            }
            2 -> {
                btn_submit_t.showSuccess()
            }
            3 -> Handler().postDelayed({
                clickCount--
                [email protected] {
                    btn_submit_t.hideLoading()
                    btn_submit_t.isEnabled
                }
            }, 1000)
        }
    }

this method is placed at the kotlin-based activity and I would like to call it from java singleton. I call this method from singleton like this:

new LoginScr().workingWithBtn(3);

but I receive the error:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference

as I understand my class can't find my button. I tried to use findViewById and then work with btn but it didn't help me. How I can solve this problem?

Andrew :

I have managed to solve my problem via BroadcastReceiver. For this solution we have to add to our singleton to the place where we will need a function call these lines:

Intent intent = new Intent();
intent.setAction("btn_task"); // name of your filter
intent.putExtra("url", 1);
context.sendBroadcast(intent); // here you won't need context but I have to use it from singleton

then we create a variable at the activity:

lateinit var receiver: BroadcastReceiver

then we will assign the value:

val filter = IntentFilter("btn_task") // we will filter all intents with our filter

and then we have to create and register our receiver:

receiver = object : BroadcastReceiver() {
            override fun onReceive(context: Context, intent: Intent) {
                workingWithBtn(intent.extras.getInt("url"))
            }
        }
registerReceiver(receiver, filter)

delete receiver when activity will be destroyed:

override fun onDestroy() {
        super.onDestroy()
        unregisterReceiver(receiver)
    }

maybe it will help someone else. Good Luck :)