How to call a method in an Activity from another class

Question

I am working on an SMS application and I have a method in my MainActivity to perform a button click:

public void updateMessage() {
    ViewMessages.performClick();
}

This method works fine and performs the button click when I call this method from inside the MainActivity class.
But, when I call this method from any other class as shown below, where I call the Main Activity's updateMessage method from the IntentServiceHandler class, I am getting a NullPointerException:

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.widget.Button.performClick()' on a null object reference

public class IntentServiceHandler extends IntentService {

    public IntentServiceHandler() {
       super("IntentServiceHandler");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        String message = intent.getStringExtra("message");
        TransactionDataBase transactionDB = new TransactionDataBase(this, 1);
        transactionDB.addMessage(message);
        MainActivity mainActivity = new MainActivity();
        mainActivity.updateMessage();
    }
}

How can I handle this?

Edit: I even tried to make the updateMessage method static, and now i get the following exception

android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

Never ever `new` an Activity. That's your first problem. Your Activity probably needs to bind to that service and handle the message — OneCricketeer, Nov 13 '16 at 06:20
update the question. i made it static, and now i am getting a different exception — God_Father, Nov 13 '16 at 06:27
`static` isn't the proper solution. Thats just a terrible workaround. — OneCricketeer, Nov 13 '16 at 06:34
Possible duplicate of [sending message from IntentService to Activity](http://stackoverflow.com/questions/12830417/sending-message-from-intentservice-to-activity) or [Intent from Service to Activity](http://stackoverflow.com/questions/12997463/send-intent-from-service-to-activity) — OneCricketeer, Nov 13 '16 at 06:34

score 1 · Answer 1 · answered Nov 13 '16 at 08:08

Don't call the method of Activity in an IntentService, try to use Intent to communicate between Activity and IntentService.

Replace the last two statements onHandleIntent() with

Intent intent = new Intent();
broadcastIntent.setAction(MainActivity.UPDATE_MESSAGE);
broadcastIntent.addCategory(Intent.CATEGORY_DEFAULT);
sendBroadcast(intent);

And you should register a BroadcastReceiver in onCreate() of MainAcitivty like

private BroadcastReceiver receiver;

@Override 
public void onCreate(Bundle savedInstanceState){

    // ....

    IntentFilter filter = new IntentFilter();
    filter.addAction(UPDATE_MESSAGE);

    receiver = new BroadcastReceiver() {
        @Override 
        public void onReceive(Context context, Intent intent) {
        // do something based on the intent's action 
        // for example, call updateMessage()
        } 
    };

    registerReceiver(receiver, filter);
}

onHandleIntent of IntentService run in another thread (instead of main thread / ui thread), so Updating UI components in onHandleIntent isn't permitted.

How to call a method in an Activity from another class

1 Answers1