Achieve geofencing using xamarin.forms

I am trying to implement geofencing through Xamarin.Forms. First I have started my work in iOS and i found a library i.e. CoreLocation, in this I am using CLCircularRegion class for making virtual boundary.
CLCircularRegion region = new CLCircularRegion(new CLLocationCoordinate2D(+28.5003615,+77.0718658), 1.0, "MDS");
But after defining the range i did not get any notification which tells any reliable information i.e. no events was fired after entering the region or leaving the region. I have read the article which gives me some information regarding Geofencing. Can any one tell me how to exactly implement geofencing in monotouch so that i can use this in my Xamarin.Forms. Please attach an example.
Thanks in advanced.