void UpdateBackbuttonBehavior()
{
var bbb = Shell.GetBackButtonBehavior(_currentPage);
if (bbb == _backButtonBehavior)
{
return;
}
if (_backButtonBehavior != null)
{
_backButtonBehavior.PropertyChanged -= OnBackButtonPropertyChanged;
}
_backButtonBehavior = bbb;
if (_backButtonBehavior != null)
{
_backButtonBehavior.PropertyChanged += OnBackButtonPropertyChanged;
}
void OnBackButtonPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
ApplyChanges();
if (_backButtonBehavior.Command == _backButtonCommand)
{
return;
}
if (_backButtonCommand != null)
{
_backButtonCommand.CanExecuteChanged -= OnBackButtonCanExecuteChanged;
}
_backButtonCommand = _backButtonBehavior.Command;
if (_backButtonCommand != null)
{
_backButtonCommand.CanExecuteChanged += OnBackButtonCanExecuteChanged;
}
}
void OnBackButtonCanExecuteChanged(object sender, EventArgs e)
{
BackButtonEnabled =
_backButtonCommand.CanExecute(_backButtonBehavior.CommandParameter);
}
}
void ApplyChanges()
{
if (_shell.CurrentPage == null)
{
return;
}
var stack = _shell.Navigation.NavigationStack;
if (stack.Count == 0)
{
return;
}
var currentPage = _shell.CurrentPage;
_toolbarTracker.Target = currentPage;
Page previousPage = null;
if (stack.Count > 1)
{
previousPage = stack[stack.Count - 1];
}
ToolbarItems = _toolbarTracker.ToolbarItems;
IsVisible = _shell.GetEffectiveValue <bool>(Shell.NavBarIsVisibleProperty, true);
_backButtonBehavior = _shell.GetEffectiveValue <BackButtonBehavior>(Shell.BackButtonBehaviorProperty, null);
bool backButtonVisible = true;
if (_backButtonBehavior != null)
{
backButtonVisible = _backButtonBehavior.IsVisible;
}
BackButtonVisible = backButtonVisible && stack.Count > 1;
Title = (!String.IsNullOrWhiteSpace(currentPage.Title)) ? currentPage.Title : _shell.Title;
TitleView = _shell.GetEffectiveValue <VisualElement>(Shell.TitleViewProperty, null);
if (currentPage != null)
{
DynamicOverflowEnabled = PlatformConfiguration.WindowsSpecific.Page.GetToolbarDynamicOverflowEnabled(currentPage);
}
}
public ShellToolbar(Shell shell) : base(shell)
{
_shell = shell;
shell.Navigated += (_, __) => ApplyChanges();
shell.PropertyChanged += (_, p) =>
{
if (p.Is(Shell.BackButtonBehaviorProperty))
{
if (_backButtonBehavior != null)
{
_backButtonBehavior.PropertyChanged -= OnBackButtonPropertyChanged;
}
_backButtonBehavior =
_shell.GetEffectiveValue <BackButtonBehavior>(Shell.BackButtonBehaviorProperty, null);
if (_backButtonBehavior != null)
{
_backButtonBehavior.PropertyChanged += OnBackButtonPropertyChanged;
}
}
else if (p.IsOneOf(
Shell.CurrentItemProperty,
Shell.FlyoutBehaviorProperty,
Shell.BackButtonBehaviorProperty))
{
ApplyChanges();
}
};
shell.HandlerChanged += (_, __) => ApplyChanges();
_backButtonBehavior =
_shell.GetEffectiveValue <BackButtonBehavior>(Shell.BackButtonBehaviorProperty, null);
if (_backButtonBehavior != null)
{
_backButtonBehavior.PropertyChanged += OnBackButtonPropertyChanged;
}
ApplyChanges();
_toolbarTracker.CollectionChanged += (_, __) => ToolbarItems = _toolbarTracker.ToolbarItems;
_toolbarTracker.AdditionalTargets = new List <Page> {
shell
};
}
