title: Flutter on page focus event?
body: <p>initState() will always call on the initialization of a page, and thats great.</p>
  
  <p>But, what if I have 2 screens </p>
  
  <p>Screen 1 navigates to screen 2. Now, when you press back on page 2 (pop) is there an event on page 1 that knows we are back again?</p>
  
  <p>In other words, can Screen 1 fire an event on the back press of page 2?</p>
  
  <p>This is useful to set the state, of say, a global variable that changed on screen 2, so screen 1 can update accordingly</p>