Added common file dialog service; upgraded to Avalonia 11.3.7

Source/CommonDialogs/IFilePickerService.cs

@@ -0,0 +1,76 @@
+#region Apache License 2.0
+/*
+Nuclex Foundation libraries for .NET
+Copyright (C) 2002-2025 Markus Ewald / Nuclex Development Labs
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+#endregion // Apache License 2.0
+
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+using Avalonia.Platform.Storage;
+
+namespace Nuclex.Avalonia.CommonDialogs {
+
+  /// <summary>Service that asks the user to pick a file to open or to save</summary>
+  /// <remarks>
+  ///   All methods here work with Avalonia's <see cref="IStorageFile" /> interface to
+  ///   support web and mobile platforms.
+  /// </remarks>
+  public interface IFilePickerService {
+
+    /// <summary>Shows a file selector asking the user where to save a file</summary>
+    /// <param name="caption">
+    ///   Caption to use for the dialog asking the user for a save location
+    /// </param>
+    /// <param name="fileTypes">File types the user can choose to save as</param>
+    /// <returns>
+    ///   A task that will provide the pre-opened file for saving or null if
+    ///   the user has canceled the file picker dialog
+    /// </returns>
+    Task<IStorageFile?> AskForSaveLocationAsync(
+      string caption, params FilePickerFileType[] fileTypes
+    );
+
+    /// <summary>Shows a file selector asking the user for a file to open</summary>
+    /// <param name="caption">
+    ///   Caption to use for the dialog asking the user to select a file
+    /// </param>
+    /// <param name="fileTypes">File types the list is filtered for by default</param>
+    /// <returns>
+    ///   A task that will provide the pre-opened file for readiong or null if
+    ///   the user has canceled the file picker dialog
+    /// </returns>
+    Task<IStorageFile?> AskForFileToOpeAsync(
+      string caption, params FilePickerFileType[] fileTypes
+    );
+
+    /// <summary>Shows a file selector asking the user for a file to open</summary>
+    /// <param name="caption">
+    ///   Caption to use for the dialog asking the user to select a file
+    /// </param>
+    /// <param name="fileTypes">File types the list is filtered for by default</param>
+    /// <returns>
+    ///   A task that will provide the pre-opened file for readiong or null if
+    ///   the user has canceled the file picker dialog
+    /// </returns>
+    Task<IReadOnlyList<IStorageFile>?> AskForFilesToOpenAsync(
+      string caption, params FilePickerFileType[] fileTypes
+    );
+
+  }
+
+} // namespace Nuclex.Avalonia.CommonDialogs