Feature: Native file pickers on Linux via the desktop portal

src/Files.App/Data/Contracts/ICommonDialogService.cs

@@ -35,6 +35,24 @@ public interface ICommonDialogService
 		/// <returns>True if the 'Open' button was clicked; otherwise, false.</returns>
 		bool Open_FileSaveDialog(nint hWnd, bool pickFoldersOnly, string[] filters, Environment.SpecialFolder defaultFolder, out string filePath);
 
+		/// <summary>
+		/// Asynchronous <see cref="Open_FileOpenDialog"/>; implementations that can should avoid blocking the calling thread.
+		/// </summary>
+		Task<(bool Result, string FilePath)> OpenFileOpenDialogAsync(nint hWnd, bool pickFoldersOnly, string[] filters, Environment.SpecialFolder defaultFolder, Guid? clientGuid = null)
+		{
+			var result = Open_FileOpenDialog(hWnd, pickFoldersOnly, filters, defaultFolder, out var filePath, clientGuid);
+			return Task.FromResult((result, filePath));
+		}
+
+		/// <summary>
+		/// Asynchronous <see cref="Open_FileSaveDialog"/>; implementations that can should avoid blocking the calling thread.
+		/// </summary>
+		Task<(bool Result, string FilePath)> OpenFileSaveDialogAsync(nint hWnd, bool pickFoldersOnly, string[] filters, Environment.SpecialFolder defaultFolder)
+		{
+			var result = Open_FileSaveDialog(hWnd, pickFoldersOnly, filters, defaultFolder, out var filePath);
+			return Task.FromResult((result, filePath));
+		}
+
 		/// <summary>
 		/// Opens a common dialog called NetworkConnectionDialog through native Win32API.
 		/// </summary>

src/Files.App/Platforms/Desktop/Services/DesktopStubServices.cs

@@ -1,7 +1,10 @@
 // Copyright (c) Files Community
 // Licensed under the MIT License.
 
+using Files.Platform.Abstractions.FileChooser;
+using Microsoft.Extensions.Logging;
 using System.Collections.Specialized;
+using System.Threading;
 
 namespace Files.App.Services.Desktop
 {
@@ -59,22 +62,74 @@ internal sealed class DesktopJumpListService : IWindowsJumpListService
 		public Task<IEnumerable<string>> GetFoldersAsync() => Task.FromResult<IEnumerable<string>>([]);
 	}
 
-	// LINUX-TODO(pickers): open file/folder choosers through the xdg-desktop-portal FileChooser; until then pickers report "cancelled"
+	// Prefer the Async methods: the synchronous ones block the calling thread while the chooser is open.
 	internal sealed class DesktopCommonDialogService : ICommonDialogService
 	{
+		private readonly IFileChooserService _fileChooser;
+		private int _unavailableLogged;
+
+		public DesktopCommonDialogService(IFileChooserService fileChooser)
+		{
+			_fileChooser = fileChooser;
+		}
+
 		public bool Open_FileOpenDialog(nint hWnd, bool pickFoldersOnly, string[] filters, Environment.SpecialFolder defaultFolder, out string filePath, Guid? clientGuid = null)
 		{
-			filePath = string.Empty;
-			return false;
+			// Synchronous fallback for callers that cannot await; it blocks the calling thread
+			var (result, path) = Task.Run(() => OpenFileOpenDialogAsync(hWnd, pickFoldersOnly, filters, defaultFolder, clientGuid)).GetAwaiter().GetResult();
+			filePath = path;
+			return result;
 		}
 
 		public bool Open_FileSaveDialog(nint hWnd, bool pickFoldersOnly, string[] filters, Environment.SpecialFolder defaultFolder, out string filePath)
 		{
-			filePath = string.Empty;
-			return false;
+			var (result, path) = Task.Run(() => OpenFileSaveDialogAsync(hWnd, pickFoldersOnly, filters, defaultFolder)).GetAwaiter().GetResult();
+			filePath = path;
+			return result;
+		}
+
+		public Task<(bool Result, string FilePath)> OpenFileOpenDialogAsync(nint hWnd, bool pickFoldersOnly, string[] filters, Environment.SpecialFolder defaultFolder, Guid? clientGuid = null)
+			=> ChooseAsync(new FileChooserRequest { PickFolder = pickFoldersOnly, Filters = ParseFilters(filters), ParentWindowId = (ulong)hWnd });
+
+		public Task<(bool Result, string FilePath)> OpenFileSaveDialogAsync(nint hWnd, bool pickFoldersOnly, string[] filters, Environment.SpecialFolder defaultFolder)
+		{
+			var folder = Environment.GetFolderPath(defaultFolder);
+			return ChooseAsync(new FileChooserRequest
+			{
+				Save = true,
+				PickFolder = pickFoldersOnly,
+				Filters = ParseFilters(filters),
+				CurrentFolder = string.IsNullOrEmpty(folder) ? null : folder,
+				ParentWindowId = (ulong)hWnd,
+			});
 		}
 
 		public bool Open_NetworkConnectionDialog(nint hWnd, bool hideRestoreConnectionCheckBox = false, bool persistConnectionAtLogon = false, bool readOnlyPath = false, string? remoteNetworkName = null, bool useMostRecentPath = false) => false;
+
+		private async Task<(bool Result, string FilePath)> ChooseAsync(FileChooserRequest request)
+		{
+			var result = await _fileChooser.ChooseAsync(request).ConfigureAwait(true);
+			if (result.Status == FileChooserStatus.Unavailable && Interlocked.Exchange(ref _unavailableLogged, 1) == 0)
+				App.Logger.LogWarning("The xdg-desktop-portal FileChooser is not available; file pickers will report cancelled.");
+
+			return result.Status == FileChooserStatus.Selected && result.Paths.Count > 0
+				? (true, result.Paths[0])
+				: (false, string.Empty);
+		}
+
+		// Filters come as [name, "*.a;*.b", name, ...] pairs
+		private static List<FileChooserFilter> ParseFilters(string[] filters)
+		{
+			var list = new List<FileChooserFilter>();
+			for (var i = 0; i + 1 < filters.Length; i += 2)
+			{
+				var patterns = filters[i + 1].Split(';', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+				if (patterns.Length > 0)
+					list.Add(new FileChooserFilter(filters[i], patterns));
+			}
+
+			return list;
+		}
 	}
 
 	// Linux has no Start Menu pins

src/Files.App/ViewModels/Dialogs/DecompressArchiveDialogViewModel.cs

@@ -136,12 +136,11 @@ private string DefaultDestinationFolderPath()
 			return string.IsNullOrEmpty(directory) ? fileName : Path.Combine(directory, fileName);
 		}
 
-		private Task SelectDestinationAsync()
+		private async Task SelectDestinationAsync()
 		{
-			bool result = CommonDialogService.Open_FileOpenDialog(MainWindow.Instance.WindowHandle, true, [], Environment.SpecialFolder.Desktop, out var filePath);
+			var (result, filePath) = await CommonDialogService.OpenFileOpenDialogAsync(MainWindow.Instance.WindowHandle, true, [], Environment.SpecialFolder.Desktop);
 			if (result)
 				DestinationFolderPath = filePath;
-			return Task.CompletedTask;
 		}
 
 		private void RefreshEncodingOptions()

src/Files.App/ViewModels/Properties/BasePropertiesPage.cs

@@ -111,7 +111,7 @@ protected override void OnNavigatedTo(NavigationEventArgs e)
 					"PNG", "*.png",
 				];
 
-				var result = CommonDialogService.Open_FileOpenDialog(hWnd, false, extensions, Environment.SpecialFolder.Desktop, out var filePath);
+				var (result, filePath) = await CommonDialogService.OpenFileOpenDialogAsync(hWnd, false, extensions, Environment.SpecialFolder.Desktop);
 				if (result)
 				{
 					ViewModel.IsAblumCoverModified = true;

src/Files.App/ViewModels/Properties/HashesViewModel.cs

@@ -195,12 +195,7 @@ private async Task OnCompareFileAsync()
 		{
 			var hWnd = Microsoft.UI.Win32Interop.GetWindowFromWindowId(_appWindow.Id);
 
-			var result = CommonDialogService.Open_FileOpenDialog(
-				hWnd,
-				false,
-				[],
-				Environment.SpecialFolder.Desktop,
-				out var filePath);
+			var (result, filePath) = await CommonDialogService.OpenFileOpenDialogAsync(hWnd, false, [], Environment.SpecialFolder.Desktop);
 
 			HashInput = result && filePath != null
 				? await CalculateFileHashAsync(filePath)

src/Files.App/ViewModels/Settings/AdvancedViewModel.cs

@@ -165,7 +165,7 @@ private async Task SetAsOpenFileDialogAsync()
 		private async Task ImportSettingsAsync()
 		{
 			string[] extensions = [Strings.ZipFileCapitalized.GetLocalizedResource(), "*.zip"];
-			bool result = CommonDialogService.Open_FileOpenDialog(MainWindow.Instance.WindowHandle, false, extensions, Environment.SpecialFolder.Desktop, out var filePath);
+			var (result, filePath) = await CommonDialogService.OpenFileOpenDialogAsync(MainWindow.Instance.WindowHandle, false, extensions, Environment.SpecialFolder.Desktop);
 			if (!result)
 				return;
 
@@ -212,7 +212,7 @@ private async Task ImportSettingsAsync()
 		private async Task ExportSettingsAsync()
 		{
 			string[] extensions = [Strings.ZipFileCapitalized.GetLocalizedResource(), "*.zip"];
-			bool result = CommonDialogService.Open_FileSaveDialog(MainWindow.Instance.WindowHandle, false, extensions, Environment.SpecialFolder.Desktop, out var filePath);
+			var (result, filePath) = await CommonDialogService.OpenFileSaveDialogAsync(MainWindow.Instance.WindowHandle, false, extensions, Environment.SpecialFolder.Desktop);
 			if (!result)
 				return;
 

src/Files.App/ViewModels/Settings/AppearanceViewModel.cs

@@ -96,15 +96,15 @@ public AppearanceViewModel(IUserSettingsService userSettingsService, IResourcesS
 
 			LoadAppThemeFontFamilyOptions();
 
-			SelectImageCommand = new RelayCommand(SelectBackgroundImage);
+			SelectImageCommand = new AsyncRelayCommand(SelectBackgroundImageAsync);
 			RemoveImageCommand = new RelayCommand(RemoveBackgroundImage);
 			CustomizeToolbarCommand = new AsyncRelayCommand(() => CommandManager.CustomizeToolbar.ExecuteAsync());
 		}
 
 		/// <summary>
 		/// Opens a file picker to select a background image
 		/// </summary>
-		private void SelectBackgroundImage()
+		private async Task SelectBackgroundImageAsync()
 		{
 			string[] extensions =
 			[
@@ -118,7 +118,7 @@ private void SelectBackgroundImage()
 				"WEBP", "*.webp",
 			];
 
-			var result = CommonDialogService.Open_FileOpenDialog(MainWindow.Instance.WindowHandle, false, extensions, Environment.SpecialFolder.MyPictures, out var filePath, _backgroundImagePickerClientGuid);
+			var (result, filePath) = await CommonDialogService.OpenFileOpenDialogAsync(MainWindow.Instance.WindowHandle, false, extensions, Environment.SpecialFolder.MyPictures, _backgroundImagePickerClientGuid);
 			if (result)
 				AppThemeBackgroundImageSource = filePath;
 		}

src/Files.App/ViewModels/Settings/GeneralViewModel.cs

@@ -4,7 +4,7 @@
 using System.Collections.Specialized;
 using Windows.Storage;
 using Windows.System;
 using static Files.App.Helpers.MenuFlyoutHelper;
 using DispatcherQueue = Microsoft.UI.Dispatching.DispatcherQueue;
 
 namespace Files.App.ViewModels.Settings
@@ -18,7 +18,7 @@
 
 		private ReadOnlyCollection<IMenuFlyoutItemViewModel>? addFlyoutItemsSource;
 
-		public RelayCommand ChangePageCommand { get; }
+		public AsyncRelayCommand ChangePageCommand { get; }
 		public RelayCommand<PageOnStartupViewModel> RemovePageCommand { get; }
 		public RelayCommand<string> AddPageCommand { get; }
 		public RelayCommand RestartCommand { get; }
@@ -86,7 +86,7 @@
 
 		public GeneralViewModel()
 		{
-			ChangePageCommand = new RelayCommand(ChangePageAsync);
+			ChangePageCommand = new AsyncRelayCommand(ChangePageAsync);
 			RemovePageCommand = new RelayCommand<PageOnStartupViewModel>(RemovePage);
 			AddPageCommand = new RelayCommand<string>(async (path) => await AddPageAsync(path));
 			RestartCommand = new RelayCommand(DoRestartAsync);
@@ -346,9 +346,9 @@
 			}
 		}
 
-		private void ChangePageAsync()
+		private async Task ChangePageAsync()
 		{
-			var result = CommonDialogService.Open_FileOpenDialog(MainWindow.Instance.WindowHandle, true, [], Environment.SpecialFolder.Desktop, out var filePath);
+			var (result, filePath) = await CommonDialogService.OpenFileOpenDialogAsync(MainWindow.Instance.WindowHandle, true, [], Environment.SpecialFolder.Desktop);
 			if (result && SelectedPageIndex >= 0)
 				PagesOnStartupList[SelectedPageIndex] = new PageOnStartupViewModel(filePath);
 		}
@@ -363,7 +363,7 @@
 		{
 			if (string.IsNullOrWhiteSpace(path))
 			{
-				bool result = CommonDialogService.Open_FileOpenDialog(MainWindow.Instance.WindowHandle, true, [], Environment.SpecialFolder.Desktop, out var filePath);
+				var (result, filePath) = await CommonDialogService.OpenFileOpenDialogAsync(MainWindow.Instance.WindowHandle, true, [], Environment.SpecialFolder.Desktop);
 				if (!result)
 					return;
 

src/Files.App/Views/Properties/LibraryPage.xaml.cs

@@ -91,7 +91,7 @@ protected override void Properties_Loaded(object sender, RoutedEventArgs e)
 
 		private async Task AddLocationAsync()
 		{
-			var result = CommonDialogService.Open_FileOpenDialog(MainWindow.Instance.WindowHandle, true, [], Environment.SpecialFolder.Desktop, out var filePath);
+			var (result, filePath) = await CommonDialogService.OpenFileOpenDialogAsync(MainWindow.Instance.WindowHandle, true, [], Environment.SpecialFolder.Desktop);
 			if (!result)
 				return;
 

src/Files.Platform.Abstractions/FileChooser/IFileChooserService.cs

@@ -0,0 +1,76 @@
+// Copyright (c) Files Community
+// Licensed under the MIT License.
+
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Files.Platform.Abstractions.FileChooser
+{
+	/// <summary>
+	/// One entry of the file type list. Each pattern is a glob such as <c>*.png</c>.
+	/// </summary>
+	public sealed record FileChooserFilter(string Name, IReadOnlyList<string> Patterns);
+
+	/// <summary>
+	/// What to ask the user for.
+	/// </summary>
+	public sealed record FileChooserRequest
+	{
+		/// <summary>Pick a folder instead of a file.</summary>
+		public bool PickFolder { get; init; }
+
+		/// <summary>Ask for a destination to write to instead of existing items.</summary>
+		public bool Save { get; init; }
+
+		/// <summary>Allow several selections (open only).</summary>
+		public bool Multiple { get; init; }
+
+		/// <summary>The dialog title; the desktop picks a default when empty.</summary>
+		public string Title { get; init; } = string.Empty;
+
+		public IReadOnlyList<FileChooserFilter> Filters { get; init; } = [];
+
+		/// <summary>The suggested file name (save only).</summary>
+		public string? CurrentName { get; init; }
+
+		/// <summary>The folder to start in (save only; the portal ignores it for open).</summary>
+		public string? CurrentFolder { get; init; }
+
+		/// <summary>The X11 window id of the parent window, or zero when unknown.</summary>
+		public ulong ParentWindowId { get; init; }
+	}
+
+	/// <summary>
+	/// How the request ended.
+	/// </summary>
+	public enum FileChooserStatus
+	{
+		/// <summary>The user chose something.</summary>
+		Selected,
+
+		/// <summary>The user dismissed the dialog or it failed.</summary>
+		Cancelled,
+
+		/// <summary>No file chooser is available on this desktop.</summary>
+		Unavailable,
+	}
+
+	/// <summary>
+	/// The outcome of a chooser request; <see cref="Paths"/> are absolute local paths.
+	/// </summary>
+	public sealed record FileChooserResult(FileChooserStatus Status, IReadOnlyList<string> Paths)
+	{
+		public static FileChooserResult Cancelled { get; } = new(FileChooserStatus.Cancelled, []);
+
+		public static FileChooserResult Unavailable { get; } = new(FileChooserStatus.Unavailable, []);
+	}
+
+	/// <summary>
+	/// Shows the desktop's own file and folder chooser.
+	/// </summary>
+	public interface IFileChooserService
+	{
+		Task<FileChooserResult> ChooseAsync(FileChooserRequest request, CancellationToken cancellationToken = default);
+	}
+}