title: Flutter Sliver pull to refresh
body: <p>I have a Sliver grid inside a CustomScrollView, I want to refresh the content when the grid is pulled down.</p>
  
  <p>I digged in the widgets, but it seems it is not easily possible. It seems it is not closely related to sliver actually, but list view. </p>
  
  <p>I tried adding a GestureDetector, but somehow couldn't make that work either. I also came across <a href="https://github.com/peng8350/flutter_pulltorefresh" rel="nofollow noreferrer">https://github.com/peng8350/flutter_pulltorefresh</a>. Even though it is very impressive, but the restrictions it applies to the widget structure, and the "hack" it had to use to make it work somehow seemed too much.</p>
  
  <p>Is there any more humane way to tap into the pull down gesture when the sliver is at the top, and essentially doesn't do much?</p>