protected virtual void OnPageSelected(int position)
{
if (_selecting)
{
return;
}
var shellSection = ShellSection;
var visibleItems = SectionController.GetItems();
// This mainly happens if all of the items that are part of this shell section
// vanish. Android calls `OnPageSelected` with position zero even though the view pager is
// empty
if (visibleItems.Count >= position)
{
return;
}
var shellContent = visibleItems[position];
if (shellContent == shellSection.CurrentItem)
{
return;
}
var stack = shellSection.Stack.ToList();
bool result = ShellController.ProposeNavigation(ShellNavigationSource.ShellContentChanged,
(ShellItem)shellSection.Parent, shellSection, shellContent, stack, true);
if (result)
{
UpdateCurrentItem(shellContent);
}
else if (shellSection?.CurrentItem != null)
{
var currentPosition = visibleItems.IndexOf(shellSection.CurrentItem);
_selecting = true;
// Android doesn't really appreciate you calling SetCurrentItem inside a OnPageSelected callback.
// It wont crash but the way its programmed doesn't really anticipate re-entrancy around that method
// and it ends up going to the wrong location. Thus we must invoke.
_viewPager.Post(() =>
{
if (currentPosition < _viewPager.ChildCount && _toolbarTracker != null)
{
_viewPager.SetCurrentItem(currentPosition, false);
UpdateCurrentItem(shellSection.CurrentItem);
}
_selecting = false;
});
}
}
void TabLayoutMediator.ITabConfigurationStrategy.OnConfigureTab(TabLayout.Tab tab, int position)
{
if (_selecting)
{
return;
}
tab.SetText(new String(SectionController.GetItems()[position].Title));
// TODO : Find a way to make this cancellable
var shellSection = ShellSection;
var shellContent = SectionController.GetItems()[position];
if (shellContent == shellSection.CurrentItem)
{
return;
}
var stack = shellSection.Stack.ToList();
bool result = ShellController.ProposeNavigation(ShellNavigationSource.ShellContentChanged,
(ShellItem)shellSection.Parent, shellSection, shellContent, stack, true);
if (result)
{
UpdateCurrentItem(shellContent);
}
else if (shellSection?.CurrentItem != null)
{
var currentPosition = SectionController.GetItems().IndexOf(shellSection.CurrentItem);
_selecting = true;
// Android doesn't really appreciate you calling SetCurrentItem inside a OnPageSelected callback.
// It wont crash but the way its programmed doesn't really anticipate re-entrancy around that method
// and it ends up going to the wrong location. Thus we must invoke.
Device.BeginInvokeOnMainThread(() =>
{
if (currentPosition < _viewPager.ChildCount && _toolbarTracker != null)
{
_viewPager.SetCurrentItem(currentPosition, false);
UpdateCurrentItem(shellSection.CurrentItem);
}
_selecting = false;
});
}
}
