var newFragment = new mybacklogF ();
var ft = FragmentManager.BeginTransaction ();
ft.Replace (Resource.Id.main_FragmentContainer, newFragment,"Homepage");
ft.AddToBackStack ("Homepage");
ft.Commit ();
后退
Button btnBack = view.FindViewById<Button> (Resource.Id.LEFT_BUTTON);
btnBack.Visibility = ViewStates.Visible;
btnBack.Click += (object sender, EventArgs e) => {
FragmentManager.PopBackStack();
};