Call fragment method inside an activity from another activity

I have an Activity A with a Fragment and an Activity B.

When I click a button inside the Fragment, the Activity B is starting and i assume that the Activity A is onPause.

What I want to do is to click on a button inside the Activity B which will finish() this Activity and then go back to the Activity A.

Doing so would automatically call a method inside the fragment. After research I tried to implements Interface and Fragment transactions but I always get null objects.

How can I make my activities communicating and pass the information to the fragment in this configuration?

Solution

Call ActivityB from FragmentA (which is part of ActivityA) as startActivityForResult() instead of startActivity() call.

Using this, you would be able to pass back result from Activity B to Fragment A.

Fragment A (Part of ActivityA) :

// Calling Activity B
Intent intent = new Intent(this, ActivityB.class); 
intent.putExtras(b);    
startActivityForResult(intent, ANY_ID);

// Overriding callback for result
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (requestCode == ANY_ID && resultCode == Activity.RESULT_OK) {
        // Your logic of receiving data from Activity B
    }
}

Important Point : The Fragment A is the one making the startActivityForResult() call, but it is part of Activity A so Activity A gets the first shot at handling the result. It has to call super.onActivityResult() so that the callback can come to Fragment A

In Activity A :

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    // This is required, in order to get onActivityResult callback in Fragment A
}

Setting result back from Activity B :

Intent resultIntent = new Intent();
// You can pass any data via this intent's bundle by putting as key-value pair
resultIntent.putExtra("Key", Value);
setResult(Activity.RESULT_OK, resultIntent);
finish();

Reference :