Is it possible to pre-populate subject field in mail when sharing a URL

In my app the users can click a share button which shows all the possible installed applications that are capable of sending a NSURL. When the user clicks Mail I want to repopulate the subject field (I'm already populating the body, which is working). Additionally when the user clicks SMS then I want to have a different message than when the user clicked Mail

Is this possible to do?

This is what I'm doing currently but not sure how to customize the message for Mail vs. SMS

  activity_vc = UIActivityViewController.alloc.initWithActivityItems(["Check it out!",
  NSURL.URLWithString("http://myurl.com/?id="+@item_id.to_s)], applicationActivities:nil)
  activity_vc.modalTransitionStyle = UIModalTransitionStyleCoverVertical
  activity_vc.excludedActivityTypes = [
    UIActivityTypeAddToReadingList,
    UIActivityTypeAirDrop,
    UIActivityTypeCopyToPasteboard,
    UIActivityTypePrint
  ]
  @delegate.presentViewController(activity_vc, animated:true, completion:nil)

Solution

You should be able to do this using setValue(forKey:)

activity_vc.setValue('Populated subject field', forKey: 'subject')