如何在反应导航中检测抽屉何时打开？

I'm using react-navigation's DrawerNavigator in my app. I would like to detect when a user drags open the side menu so that i can perform a certain action, e.g dismiss an opened Keyboard. How can i do this? i can't seem to find a solution in the docs. Thank you.I'm using react-navigation's DrawerNavigator in