VeloeAvaloniaKemonoPartyApplication/VeloeAvaloniaKemonoPartyApp/VeloeAvaloniaKemonoPartyApp/Services/StorageService.cs

using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Controls;
using Avalonia.Platform.Storage;
using System;
using System.Threading.Tasks;
using Avalonia;
using Avalonia.VisualTree;

namespace VeloeAvaloniaKemonoPartyApp.Services
{
    public class StorageService
    {
        protected virtual IStorageProvider Storage => _storage ??= GetTopLevel()?.StorageProvider ?? throw new NullReferenceException("No StorageProvider found.");
        private IStorageProvider? _storage;

        public async Task<string?> GetDocumentsFolderAsync()
        {
            var result = await Storage.TryGetWellKnownFolderAsync(WellKnownFolder.Documents);
            return result.TryGetLocalPath();
        }

        public async Task<string?> GetPicturesFolderAsync()
        {
            var result = await Storage.TryGetWellKnownFolderAsync(WellKnownFolder.Pictures);
            return result.TryGetLocalPath();
        }

        private TopLevel? GetTopLevel()
        {
            if (Application.Current?.ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
            {
                return desktop.MainWindow;
            }
            if (Application.Current?.ApplicationLifetime is ISingleViewApplicationLifetime viewApp)
            {
                var visualRoot = viewApp.MainView?.GetVisualRoot();
                return visualRoot as TopLevel;
            }
            return null;
        }
    }
}