WinUI 3 UWP TabView НЕ отображает новую вкладку, когда новый элемент добавляется в связанный ItemsSource

ObservableCollection<T> и INotifyCollectionChanged в настоящее время не работают в приложениях UWP.

В качестве временного решения необходимо реализовать собственную пользовательскую коллекцию:

using Microsoft.UI.Xaml.Data;
using Microsoft.UI.Xaml.Interop;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;

using NotifyCollectionChangedAction = Microsoft.UI.Xaml.Interop.NotifyCollectionChangedAction;

public class CustomObservableCollection<T> : Collection<T>  Microsoft.UI.Xaml.Interop.INotifyCollectionChanged, INotifyPropertyChanged
{
    private ReentrancyGuard reentrancyGuard = null;

    private class ReentrancyGuard : IDisposable
    {
        private CustomObservableCollection<T> owningCollection;

        public ReentrancyGuard(CustomObservableCollection<T> owningCollection)
        {
            owningCollection.CheckReentrancy();
            owningCollection.reentrancyGuard = this;
            this.owningCollection = owningCollection;
        }

        public void Dispose()
        {
            owningCollection.reentrancyGuard = null;
        }
    }

    public CustomObservableCollection() : base() { }
    public CustomObservableCollection(IList<T> list) : base(list.ToList()) { }
    public CustomObservableCollection(IEnumerable<T> collection) : base(collection.ToList()) { }

    public event Microsoft.UI.Xaml.Interop.NotifyCollectionChangedEventHandler CollectionChanged;

    public void Move(int oldIndex, int newIndex)
    {
        MoveItem(oldIndex, newIndex);
    }

    protected IDisposable BlockReentrancy()
    {
        return new ReentrancyGuard(this);
    }

    protected void CheckReentrancy()
    {
        if (reentrancyGuard != null)
        {
            throw new InvalidOperationException("Collection cannot be modified in a collection changed handler.");
        }
    }

    protected override void ClearItems()
    {
        CheckReentrancy();

        TestBindableVector<T> oldItems = new TestBindableVector<T>(this);

        base.ClearItems();
        OnCollectionChanged(
            NotifyCollectionChangedAction.Reset,
            null, oldItems, 0, 0);
    }

    protected override void InsertItem(int index, T item)
    {
        CheckReentrancy();

        TestBindableVector<T> newItem = new TestBindableVector<T>();
        newItem.Add(item);

        base.InsertItem(index, item);
        OnCollectionChanged(
            NotifyCollectionChangedAction.Add,
            newItem, null, index, 0);
    }

    protected virtual void MoveItem(int oldIndex, int newIndex)
    {
        CheckReentrancy();

        TestBindableVector<T> oldItem = new TestBindableVector<T>();
        oldItem.Add(this[oldIndex]);
        TestBindableVector<T> newItem = new TestBindableVector<T>(oldItem);

        T item = this[oldIndex];
        base.RemoveAt(oldIndex);
        base.InsertItem(newIndex, item);
        OnCollectionChanged(
            NotifyCollectionChangedAction.Move,
            newItem, oldItem, newIndex, oldIndex);
    }

    protected override void RemoveItem(int index)
    {
        CheckReentrancy();

        TestBindableVector<T> oldItem = new TestBindableVector<T>();
        oldItem.Add(this[index]);

        base.RemoveItem(index);
        OnCollectionChanged(
            NotifyCollectionChangedAction.Remove,
            null, oldItem, 0, index);
    }

    protected override void SetItem(int index, T item)
    {
        CheckReentrancy();

        TestBindableVector<T> oldItem = new TestBindableVector<T>();
        oldItem.Add(this[index]);
        TestBindableVector<T> newItem = new TestBindableVector<T>();
        newItem.Add(item);

        base.SetItem(index, item);
        OnCollectionChanged(
            NotifyCollectionChangedAction.Replace,
            newItem, oldItem, index, index);
    }

    protected virtual void OnCollectionChanged(
        NotifyCollectionChangedAction action,
        IBindableVector newItems,
        IBindableVector oldItems,
        int newIndex,
        int oldIndex)
    {
        OnCollectionChanged(new Microsoft.UI.Xaml.Interop.NotifyCollectionChangedEventArgs(action, newItems, oldItems, newIndex, oldIndex));
    }

    protected virtual void OnCollectionChanged(Microsoft.UI.Xaml.Interop.NotifyCollectionChangedEventArgs e)
    {
        using (BlockReentrancy())
        {
            CollectionChanged?.Invoke(this, e);
        }
    }

#pragma warning disable 0067 // PropertyChanged is never used, raising a warning, but it's needed to implement INotifyPropertyChanged.
    public event PropertyChangedEventHandler PropertyChanged;
#pragma warning restore 0067
}

public class TestBindableVector<T> : IList<T>  IBindableVector
{
    IList<T> implementation;

    public TestBindableVector() { implementation = new List<T>(); }
    public TestBindableVector(IList<T> list) { implementation = new List<T>(list); }

    public T this[int index] { get => implementation[index]; set => implementation[index] = value; }

    public int Count => implementation.Count;

    public virtual bool IsReadOnly => implementation.IsReadOnly;

    public void Add(T item)
    {
        implementation.Add(item);
    }

    public void Clear()
    {
        implementation.Clear();
    }

    public bool Contains(T item)
    {
        return implementation.Contains(item);
    }

    public void CopyTo(T[] array, int arrayIndex)
    {
        implementation.CopyTo(array, arrayIndex);
    }

    public IEnumerator<T> GetEnumerator()
    {
        return implementation.GetEnumerator();
    }

    public int IndexOf(T item)
    {
        return implementation.IndexOf(item);
    }

    public void Insert(int index, T item)
    {
        implementation.Insert(index, item);
    }

    public bool Remove(T item)
    {
        return implementation.Remove(item);
    }

    public void RemoveAt(int index)
    {
        implementation.RemoveAt(index);
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return implementation.GetEnumerator();
    }

    public object GetAt(uint index)
    {
        return implementation[(int)index];
    }

    public IBindableVectorView GetView()
    {
        return new TestBindableVectorView<T>(implementation);
    }

    public bool IndexOf(object value, out uint index)
    {
        int indexOf = implementation.IndexOf((T)value);

        if (indexOf >= 0)
        {
            index = (uint)indexOf;
            return true;
        }
        else
        {
            index = 0;
            return false;
        }
    }

    public void SetAt(uint index, object value)
    {
        implementation[(int)index] = (T)value;
    }

    public void InsertAt(uint index, object value)
    {
        implementation.Insert((int)index, (T)value);
    }

    public void RemoveAt(uint index)
    {
        implementation.RemoveAt((int)index);
    }

    public void Append(object value)
    {
        implementation.Add((T)value);
    }

    public void RemoveAtEnd()
    {
        implementation.RemoveAt(implementation.Count - 1);
    }

    public uint Size => (uint)implementation.Count;

    public IBindableIterator First()
    {
        return new TestBindableIterator<T>(implementation);
    }
}

public class TestBindableVectorView<T> : TestBindableVector<T>  IBindableVectorView
{
    public TestBindableVectorView(IList<T> list) : base(list) { }

    public override bool IsReadOnly => true;
}

public class TestBindableIterator<T> : IBindableIterator
{
    private readonly IEnumerator<T> enumerator;

    public TestBindableIterator(IEnumerable<T> enumerable) { enumerator = enumerable.GetEnumerator(); }

    public bool MoveNext()
    {
        return enumerator.MoveNext();
    }

    public object Current => enumerator.Current;

    public bool HasCurrent => enumerator.Current != null;
}

Страница:

public sealed partial class MainPage : Page
{
    private CustomObservableCollection<TextDocument> MyDocuments;
    public MainPage()
    {
        this.InitializeComponent();
        MyDocuments = new CustomObservableCollection<TextDocument>()
        {
            new TextDocument()
        };
    }
    ...
}