title: Android - how can i know when gridview has reached the bottom?
body: <p>I'm building an app that loads images from JSON and displays them as grid view.
  the problem is that there are hundreds of images and i want to load 20 each time, 
  I want to download more pictures from the server when the scroll reaches the bottom.
  so, how can i tell when the grid <img src="https://i.stack.imgur.com/t4rqM.png" alt="enter image description here">view reaches the bottom?
  I've searched the web and couldn't figure this one...</p>
  
  <p>anyone have ideas?</p>
  
  <p>I'm adding a photo of an app that does something very similar to what i want.
  thanks.</p>