feat: Implement FileSavePicker for Gtk

Author: Youssef1313

doc/articles/features/windows-storage-pickers.md

@@ -12,7 +12,7 @@ Legend
 | Picker         | UWP   | WebAssembly | Android | iOS   | macOS | WPF | GTK |
 |----------------|-------|-------------|---------|-------|-------|-----|-----|
 | FileOpenPicker | ✔️   | ✔️  (1)     | ✔️     | ✔️    | ✔️   | ✔️  | ✔️  |
-| FileSavePicker | ✔️   | ✔️  (1)     | ✔️     | ✔️    | ✔️   | ✔️  | ❌  |
+| FileSavePicker | ✔️   | ✔️  (1)     | ✔️     | ✔️    | ✔️   | ✔️  | ✔️  |
 | FolderPicker   | ✔️   | ✔️          | ✔️     | 💬 (2)| ✔️   | ❌  | ✔️  |
 
 *(1) - Multiple implementations supported - see WebAssembly section below*

src/Uno.UI.Runtime.Skia.Gtk/Extensions/Storage/Pickers/FileSavePickerExtension.cs

@@ -0,0 +1,51 @@
+#nullable enable
+
+using Gtk;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Uno.UI.Runtime.Skia;
+using Windows.Storage;
+using Windows.Storage.Pickers;
+
+namespace Uno.Extensions.Storage.Pickers
+{
+	internal class FileSavePickerExtension : IFileSavePickerExtension
+	{
+		private readonly FileSavePicker _picker;
+
+		public FileSavePickerExtension(FileSavePicker owner)
+		{
+			_picker = owner ?? throw new ArgumentNullException(nameof(owner));
+		}
+
+		public async Task<StorageFile?> PickSaveFileAsync(CancellationToken token)
+		{
+			string commitText = "Save File";
+			if (!string.IsNullOrWhiteSpace(_picker.CommitButtonText))
+			{
+				commitText = _picker.CommitButtonText;
+			}
+
+			FileChooserDialog dialog = new FileChooserDialog(
+			"Save File",
+			GtkHost.Window,
+			FileChooserAction.Save,
+			"Cancel", ResponseType.Cancel,
+			commitText, ResponseType.Accept);
+
+			dialog.SelectMultiple = false;
+			dialog.SetFilename(_picker.SuggestedFileName);
+			dialog.SetCurrentFolder(PickerHelpers.GetInitialDirectory(_picker.SuggestedStartLocation));
+
+			StorageFile? file = null;
+			if (dialog.Run() == (int)ResponseType.Accept)
+			{
+				file = await StorageFile.GetFileFromPathAsync(dialog.Filename);
+			}
+
+			dialog.Destroy();
+			return file;
+		}
+	}
+}

src/Uno.UI.Runtime.Skia.Gtk/GtkHost.cs

@@ -64,6 +64,7 @@ public void Run()
 			ApiExtensibility.Register<FileOpenPicker>(typeof(IFileOpenPickerExtension), o => new FileOpenPickerExtension(o));
 			ApiExtensibility.Register<FolderPicker>(typeof(IFolderPickerExtension), o => new FolderPickerExtension(o));
 			ApiExtensibility.Register(typeof(IClipboardExtension), o => new ClipboardExtensions(o));
+			ApiExtensibility.Register<FileSavePicker>(typeof(IFileSavePickerExtension), o => new FileSavePickerExtension(o));
 
 			_isDispatcherThread = true;
 			_window = new Gtk.Window("Uno Host");