Corrado Cavalli

Unfortunately TapGestureRecognizer doesn't inherit the BindingContext so EventToCommand's BindingContext is null and CommandParameter's binding fails, that's where the null comes from. Being part of GestureRecognizers collection there's no way to...

I see, cool, let's see their implementation...

You can bind ListView's SelectedItem property to the ViewModel using Mode=TwoWay or, if you want to use ItemTapped event you can try this example: http://pastebin.com/Hx3T8qVQ