How to trigger a function on a old Activity when returning from a newer activity? [duplicate]

Answer 1

You should use below method to start your activity

static final int YOUR_REQUEST_CODE = 1;  // The request code
startActivityForResult(yourIntent, YOUR_REQUEST_CODE);

And then, in the OLD activity, override below method:

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    // Check which request we're responding to
    if (requestCode == YOUR_REQUEST_CODE) {
        // Make sure the request was successful
        if (resultCode == RESULT_OK) {

            // Do something with here.
        }
    }
}

More details can be found at Android Developer Official Guide