title: Communication between two fragments, each in it's own Activity
body: <p>I found a lot of answers about communicating between fragment and it's Activity but it was always description of communication between fragment and it's own Activity. I couldn't find a description how to communicate between fragments in different Activities.</p>
  
  <p><strong>I have the following scenario:</strong>
  I have ItemsActivity containing ItemsFragment with a list of items.
  User scrolls through items and clicks to some item.
  Then ItemsFragment creates an instance of new Activity: DetailActivity containing DetailFragment where is implemented detail view of item. 
  User modifies data of the item and clicks back (or to some save button).
  Data of the modified item is saved and the DetailActivity is destroyed and removed from back stack.
  User is back in the ItemsActivity/ItemsFragment containing a list of items.</p>
  
  <p><strong>Question:</strong> The DetailFragment should notify the ItemsFragment, that the item was modified so the ItemsFragment should update it's view in the item list. 
  Problem is that the DetailFragment knows nothing about the ItemsFragment in the different Activity (ItemsActivity). How to notify the ItemsFragment in the ItemsActivity from the DetailFragment, that item was changed and the item's view in the list shoud be updated?</p>