Navigation Page in Tabbed Page

public class mainNav : TabbedPage
    {
        public mainNav ()
        {
            Children.Add(new NavigationPage (new Page1 ()) {
                Title = "1",
                BarBackgroundColor = Color.FromRgb (255, 69, 0),
                BarTextColor = Color.White,
            });
            Children.Add(new NavigationPage (new Page2 ()) {
                Title = "2",
                BarBackgroundColor = Color.FromRgb (255, 69, 0),
                BarTextColor = Color.White,
            });
            Children.Add(new NavigationPage (new Page3 ()) {
                Title = "3",
                BarBackgroundColor = Color.FromRgb (255, 69, 0),
                BarTextColor = Color.White,
            });
            Children.Add(new NavigationPage (new Page4 ()) {
                Title = "4",
                BarBackgroundColor = Color.FromRgb (255, 69, 0),
                BarTextColor = Color.White,
            });
        }
    }

As I build them, It worked on Android. But on iOS, it doesn't work. Are there anything to do I missed?