Use $evalAsync instead of $apply

In my application, onDrop callback is called in $digest cycle, and crash because of famous error :

Error: [$rootScope:inprog] $apply already in progress
http://errors.angularjs.org/1.3.2/$rootScope/inprog?p0=%24apply

This fixes the issue by replacing $apply call by $evalAsync.

See this blog article : http://www.bennadel.com/blog/2605-scope-evalasync-vs-timeout-in-angularjs.htm