Avalonia/PortfolioManager/Views/MainWindow.axaml.cs

using System.ComponentModel;
using Avalonia.Controls;
using Avalonia.Controls.Primitives;
using Avalonia.Controls.Templates;
using PortfolioManager.ViewModels;

namespace PortfolioManager.Views;

public partial class MainWindow : Window
{
    private TabControl tabControl = null;

    public MainWindow()
    {
        InitializeComponent();
    }

    private void tabControl_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (null == tabControl)
        {
            tabControl = (TabControl)sender;
            MainWindowViewModel viewModel = (MainWindowViewModel)DataContext;
            viewModel.OnIndexChangeEventHandler += OnIndexChangeEvent;
        }
    }

    protected void OnIndexChangeEvent(object sender, TabIndexArgs args)
    {
        if (null == tabControl) return;
        tabControl.SelectedIndex = args.Index;
    }
}