code_snippet2.java

// Check whether back stack exists.
if (Referrers.hasReferrer(getIntent())) {
  // If the current back stack exists just navigate to parent activity.
  Class parentActivityClass = Referrers.getReferrer(getIntent());
  Intent intent = new Intent(this, parentActivityClass).setFlags(FLAG_ACTIVITY_CLEAR_TOP | FLAG_ACTIVITY_SINGLE_TOP);

  this.startActivity(intent);
} else {
  // If ItemDetailsActivity was open for example from the notification then create back stack manually.
  Intent collectionsIntent = ContentCollectionActivity.createIntent(this, null);
  Intent mainActivityIntent = new Intent(this, MainActivity.class);

  TaskStackBuilder.create(this)
    .addNextIntent(mainActivityIntent)
    .addNextIntent(collectionsIntent)
    .startActivities();
}