public override void PrepareForSegue (UIStoryboardSegue segue, NSObject sender)
{
if (segue.Identifier != "addBeerSegue")
return;
// set in Storyboard
var navctlr = segue.DestinationViewController as AddBeerTableViewController;
if (navctlr == null)
return;
navctlr.SetBeer (viewModel.Beer);
}