EbayListingTool/EbayListingTool/App.xaml.cs

using System.Threading.Tasks;
using System.Windows;
using System.Windows.Threading;
using Microsoft.Extensions.Configuration;

namespace EbayListingTool;

public partial class App : Application
{
    public static IConfiguration Configuration { get; private set; } = null!;

    protected override void OnStartup(StartupEventArgs e)
    {
        // Global handler for unhandled exceptions on the UI thread
        DispatcherUnhandledException += OnDispatcherUnhandledException;

        // Global handler for unhandled exceptions on background Task threads
        TaskScheduler.UnobservedTaskException += OnUnobservedTaskException;

        // Global handler for unhandled exceptions on non-UI threads
        AppDomain.CurrentDomain.UnhandledException += OnDomainUnhandledException;

        Configuration = new ConfigurationBuilder()
            .SetBasePath(AppContext.BaseDirectory)
            .AddJsonFile("appsettings.json",         optional: true,  reloadOnChange: false)
            .AddJsonFile("appsettings.local.json",   optional: true,  reloadOnChange: false)
            .Build();

        base.OnStartup(e);
    }

    private void OnDispatcherUnhandledException(object sender, DispatcherUnhandledExceptionEventArgs e)
    {
        MessageBox.Show(
            $"An unexpected error occurred:\n\n{e.Exception.Message}",
            "Unexpected Error",
            MessageBoxButton.OK,
            MessageBoxImage.Error);
        e.Handled = true; // Prevent crash; remove this line if you want fatal errors to still terminate
    }

    private void OnUnobservedTaskException(object? sender, UnobservedTaskExceptionEventArgs e)
    {
        e.SetObserved();
        Dispatcher.InvokeAsync(() =>
        {
            MessageBox.Show(
                $"A background operation failed:\n\n{e.Exception.InnerException?.Message ?? e.Exception.Message}",
                "Background Error",
                MessageBoxButton.OK,
                MessageBoxImage.Warning);
        });
    }

    private void OnDomainUnhandledException(object sender, UnhandledExceptionEventArgs e)
    {
        var message = e.ExceptionObject is Exception ex
            ? ex.Message
            : e.ExceptionObject?.ToString() ?? "Unknown error";

        MessageBox.Show(
            $"A fatal error occurred and the application must close:\n\n{message}",
            "Fatal Error",
            MessageBoxButton.OK,
            MessageBoxImage.Error);
    }
}