title: Best way to track time on view in React-Native
body: <p>I'm trying to keep track of how much time a user spends on a given view in a react native iOS app, and then send it to Parse as a custom analytics item. What's the best way to do this?</p>
  
  <p>My initial thought was to track the start time and exit time in the code used to generate a each individual page, but I was hoping there would be a more elegant way. Basically what I'm after is the amount of time that each view spends on top of the navigator stack. </p>