void navigation_BeginTransition(object sender, ChangedEventArgs<int> e)
{
inTransition = true;
int index = e.NewValue;
transitionTabItem = pages[e.NewValue];
string title = Title;
header.AnimLabel.Text = back ? title : transitionTabItem.Title;
Title = back ? transitionTabItem.Title : title;
#if SUPPORT_ALPHA
ButtonGroup bg = EnsureAnimButtons();
bg.BeginInit();
bg.Buttons.Clear();
foreach (FluidButton b in tabs[index].Buttons) bg.Buttons.Add(b);
bg.EndInit();
FluidButton back = EnsureAnimBackButton();
back.Alpha = 0;
back.Visible = index > 0;
back.Text = index > 0 ? tabs[index - 1].Title : "";
bg.Visible = bg.Buttons.Count > 0;
bg.Alpha = 0;
#endif
}
