I tried to parse text data (containing strings and a link) for share, the thing is that for anything other than Facebook it sends the data as expected, but for the Facebook it does only parse the links.
Here's my code used for the share:
var item = NSObject.FromObject("Hello World !" + "\r\n" + "http://www.google.com");
var activityItems = new NSObject[] { item };
UIActivity[] applicationActivities = null;
var activityController = new UIActivityViewController(activityItems, applicationActivities);
PresentViewController(activityController, true, null);