The usage of an UIActivityViewController in iOS/Xamarin is pretty simple. A few lines of code and you get following:
See the gist below for the source code. The usage comes down to:
var activityViewController = new ActivityViewController("Hello world"); activityViewController.PresentActivityViewController(this, true);
But there is a little caveat: On iPads you must anchor the overlay to the button, which opened it. And thats only in iOS 8. So watch out for line 52. We dont have this often in Xamarin / iOS, but it happens.