public void RegisterBackButtonHandler(IBackButtonHandler handler)
{
if (!this.backButtonHandlers.Contains(handler))
{
this.backButtonHandlers.Add(handler);
}
}
public void UnregisterBackButtonHandler(IBackButtonHandler handler)
{
if (this.backButtonHandlers.Contains(handler))
{
this.backButtonHandlers.Remove(handler);
}
}
/// <inheritdoc/>
public void RemoveHandler(IBackButtonHandler handler)
{
handler = handler ?? throw new ArgumentNullException(nameof(handler));
var entry = _handlers.FirstOrDefault(e => e.Handler == handler);
if (entry == null)
{
throw new KeyNotFoundException($"The specified handler named '{handler.Name}' was not found.");
}
_handlers.Remove(entry);
}
public async override void OnBackPressed()
{
IBackButtonHandler backButtonHandler = null;
ViewModelBase viewModel = null;
foreach (var fragment in this.GetFragmentManager().Fragments)
{
var page = fragment.GetType().GetProperty("Page")?.GetValue(fragment);
if (page is StartPageView)
{
viewModel = (ViewModelBase)(page as StartPageView).BindingContext;
if (viewModel.NavigationService.PreviousPageViewModel is StartPageViewModel)
{
backButtonHandler = viewModel as IBackButtonHandler;
}
}
if (page is LinkItemView)
{
viewModel = (ViewModelBase)(page as LinkItemView).BindingContext;
if (viewModel.NavigationService.PreviousPageViewModel is LinkItemViewModel)
{
backButtonHandler = viewModel as IBackButtonHandler;
}
}
if (page is OptionsView)
{
viewModel = (ViewModelBase)(page as OptionsView).BindingContext;
if (viewModel.NavigationService.PreviousPageViewModel is OptionsViewModel)
{
backButtonHandler = viewModel as IBackButtonHandler;
}
}
if (backButtonHandler != null)
{
break;
}
}
var backButtonHandled = await backButtonHandler?.HandleBackButton(viewModel);
if (!backButtonHandled)
{
base.OnBackPressed();
}
}
/// <inheritdoc/>
public void AddHandler(IBackButtonHandler handler, int?priority = null)
{
handler = handler ?? throw new ArgumentNullException(nameof(handler));
int entryPriority = priority ?? (_handlers.Any() ? _handlers.Max(e => e.Priority) + DefaultPriorityIncrement : DefaultPriorityIncrement);
var entry = new BackButtonHandlerEntry(handler, entryPriority);
_handlers.Add(entry);
_handlers.Sort(comparison: CompareEntries);
// Sorts by Priority, high to low.
int CompareEntries(BackButtonHandlerEntry left, BackButtonHandlerEntry right)
{
return(right.Priority.CompareTo(left.Priority));
}
}
/// <summary>
/// Creates a new instance of <see cref="BackButtonHandlerEntry"/>.
/// </summary>
public BackButtonHandlerEntry(IBackButtonHandler handler, int priority)
{
Handler = handler;
Priority = priority;
}
public void UnregisterBackButtonHandler(IBackButtonHandler handler)
{
}
/// <summary>
/// Adds a <see cref="IBackButtonHandler"/> and return an <see cref="IDisposable"/> to conveniently remove it later.
/// </summary>
/// <param name="backButtonManager"></param>
/// <param name="handler">The handler to add.</param>
/// <param name="priority">The optional priority.</param>
/// <returns>A disposable that will remove the handler when <see cref="IDisposable.Dispose"/> is invoked.</returns>
public static IDisposable RegisterHandler(this IBackButtonManager backButtonManager, IBackButtonHandler handler, int?priority = null)
{
backButtonManager.AddHandler(handler, priority);
return(new ActionDisposable(RemoveHandler));
void RemoveHandler()
{
backButtonManager.RemoveHandler(handler);
}
}
