FAB on click start new activity based on fragment currently shown

I am trying to figure a good way to start an activity from a click on the floating action button.
My FAB is located in mainactivity.xml. My MainActivity consists of bottom navigation with fragments. I need to implement a different on click action determined by a fragment that is shown.

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab_add);
fab.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
    fabClicked();
    }
});

fabClicked Method

public void fabClicked() {
    Object id = getSupportFragmentManager().findFragmentById(R.id.container);


    if ((getSupportFragmentManager().findFragmentById(R.id.fragment_1)).equals(id)) {
        Intent intent1 = new Intent(MainActivity.this, Add1.class);
        startActivity(intent1);
    }

    else if ((getSupportFragmentManager().findFragmentById(R.id.fragment_2)).equals(id)) {
        Intent intent2 = new Intent(MainActivity.this, Add2.class);
        startActivity(intent2);
    }

    else if ((getSupportFragmentManager().findFragmentById(R.id.fragment_3)).equals(id)) {
        Intent intent3 = new Intent(MainActivity.this, Add3.class);
        startActivity(intent3);
    }
    else if ((getSupportFragmentManager().findFragmentById(R.id.fragment_home)).equals(id)) {
        //plan to add to code to hide fab on homescreen
    }

}

One simple solution for this is :

Whenever the bottom navigation is used, just save the selected fragment id in a static variable and when the user presses the FAB, just open the activity based on the fragment stored in variable.

Your approach is good, but it's doing many unnecessary expensive Fragment lookups.

You can get the navigation id of the current Fragment with:

navController.getCurrentDestination().getId()

You can then use this returned id to do different things in the click listener based on the Fragment, like so:

fun fabClicked() {
    val id = navController.getCurrentDestination().getId()
    val class = when(id) {
        R.id.fragment_1 -> Add1::class
        R.id.fragment_2 -> Add2::class
        // etc
    }
    startActivity(Intent(this, class.javaClass))
}

In this way, you don't need to do Fragment look-ups for each condition, just simply compare ids. You can also extract the shared startActivity logic (as shown here) to make this much more concise.