title: iOS: Notify other tabbed view controllers about a change in its dataset
body: <p>I have a tab bar controller and inside it two controllers: a mapview controller and a tableview + NSFetcheddata controller. Both display info about a specific day from core data and have a button to display a day selector modally.</p>
  
  <p>I have achieved having my controllers dataset changing when their modal view controller disappears through delegation but I would like the two controllers to update their data and not only the one who displayed the modal controller.</p>
  
  <p>I thought about creating a protocol in both controllers and setting each other as its delegate but I would like to know if I'm doing right here.</p>
  
  <p>Cheers,</p>
  
  <p>Thierry</p>