inabox/InABox.Avalonia/Components/PageStack/PageStack.cs

using System.Collections.ObjectModel;
using System.Collections.Specialized;
using Avalonia;
using Avalonia.Controls;
using Avalonia.Controls.Primitives;
using Avalonia.Metadata;
using Avalonia.Threading;

namespace InABox.Avalonia.Components;

public class PageStack : ContentControl
{
    
    private static readonly StyledProperty<PageStackItem?> SelectedItemProperty = 
        AvaloniaProperty.Register<PageStack,PageStackItem?>(nameof(SelectedItem));
    
    private static readonly StyledProperty<int> SelectedIndexProperty = 
        AvaloniaProperty.Register<PageStack, int>(nameof(SelectedIndex), -1);
    
    static PageStack()
    {
        
        SelectedIndexProperty.Changed.AddClassHandler<PageStack>((stack,args) =>
            stack?.SelectPage((int)(args.NewValue ?? -1)));
        
        SelectedItemProperty.Changed.AddClassHandler<PageStack>((stack,args) =>
            stack?.SelectPage(args.NewValue as PageStackItem));
    }
    
    public PageStack()
    {
        var items = new ObservableCollection<PageStackItem>();
        items.CollectionChanged += ItemsChanged;
        Items = items;
    }
    
    [Content]
    public IList<PageStackItem> Items { get; private set; }
    
    public void SelectPage(int page)
    {
        SelectPage((page > -1) && (page < Items.Count) ? Items[page] : null);
    }

    private PageStackItem? _current;
    public void SelectPage(PageStackItem? page)
    {
        if (_current != null)
            _current.DoDisappearing();
        _current = page;
        Content = _current?.Content;
        _current?.DoAppearing();
        SelectionChanged?.Invoke(this, EventArgs.Empty);
    }
    
    public int SelectedIndex
    {
        get => GetValue(SelectedIndexProperty);
        set => SetValue(SelectedIndexProperty, value);
    }
    
    public PageStackItem? SelectedItem 
    {
        get => GetValue(SelectedItemProperty);
        set => SetValue(SelectedItemProperty, value);
    }
    
    public event EventHandler SelectionChanged;

    public void DoSelectionChanged()
    {
        SelectionChanged?.Invoke(this, EventArgs.Empty);
    }
    
    private void ItemsChanged(object? sender, NotifyCollectionChangedEventArgs? e)
    {
        Dispatcher.UIThread.Post(() =>
        {
            SelectedItem ??= Items.FirstOrDefault();
        });
    }
    
}