Add win32 package and base dialog wrapper class.

Add methods of FileDialogController

Add FileDialogController tests.

Extract the interface conversion to a new class to make it testable.

Add DialogWrapper constructor.

Add test constructor to DialogWrapper and add two tests.

Add mock for FileDialogController and tests for implemented methods.

free memory allocations

remove unused properties in dialog_wrapper

use Arena

Return the value of the path.

fix extension string list to remove trailing semicolon

Author: eugerossetto

packages/file_selector/file_selector_windows/lib/src/file_selector_dart/dialog_mode.dart

@@ -0,0 +1,12 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/// The kind of file dialog to show.
+enum DialogMode {
+  /// Used for chosing files.
+  Open,
+
+  /// Used for chosing a directory to save a file.
+  Save
+}

packages/file_selector/file_selector_windows/lib/src/file_selector_dart/dialog_wrapper.dart

@@ -0,0 +1,197 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:core';
+import 'dart:ffi';
+
+import 'package:ffi/ffi.dart';
+import 'package:file_selector_platform_interface/file_selector_platform_interface.dart';
+import 'package:flutter/cupertino.dart';
+import 'package:win32/win32.dart';
+
+import 'dialog_mode.dart';
+import 'file_dialog_controller.dart';
+import 'ifile_dialog_controller_factory.dart';
+import 'ifile_dialog_factory.dart';
+import 'shell_win32_api.dart';
+
+/// Wraps an IFileDialog, managing object lifetime as a scoped object and
+/// providing a simplified API for interacting with it as needed for the plugin.
+class DialogWrapper {
+  /// Creates a DialogWrapper using a [IFileDialogControllerFactory] and a [DialogMode].
+  /// It is also responsible of creating a [IFileDialog].
+  DialogWrapper(IFileDialogControllerFactory fileDialogControllerFactory,
+      IFileDialogFactory fileDialogFactory, this._dialogMode)
+      : _isOpenDialog = _dialogMode == DialogMode.Open {
+    try {
+      final IFileDialog dialog = fileDialogFactory.createInstace(_dialogMode);
+      _dialogController = fileDialogControllerFactory.createController(dialog);
+      _shellWin32Api = ShellWin32Api();
+    } catch (ex) {
+      if (ex is WindowsException) {
+        _lastResult = ex.hr;
+      }
+    }
+  }
+
+  /// Creates a DialogWrapper for testing purposes.
+  @visibleForTesting
+  DialogWrapper.withFakeDependencies(FileDialogController dialogController,
+      this._dialogMode, this._shellWin32Api)
+      : _isOpenDialog = _dialogMode == DialogMode.Open,
+        _dialogController = dialogController;
+
+  int _lastResult = S_OK;
+
+  final DialogMode _dialogMode;
+
+  final bool _isOpenDialog;
+
+  final String _allowAnyValue = 'Any';
+
+  final String _allowAnyExtension = '*.*';
+
+  late FileDialogController _dialogController;
+
+  late ShellWin32Api _shellWin32Api;
+
+  /// Returns the result of the last Win32 API call related to this object.
+  int get lastResult => _lastResult;
+
+  /// Attempts to set the default folder for the dialog to [path], if it exists.
+  void setFolder(String path) {
+    if (path == null || path.isEmpty) {
+      return;
+    }
+
+    using((Arena arena) {
+      final Pointer<GUID> ptrGuid = GUIDFromString(IID_IShellItem);
+      final Pointer<Pointer<COMObject>> ptrPath = arena<Pointer<COMObject>>();
+      _lastResult =
+          _shellWin32Api.createItemFromParsingName(path, ptrGuid, ptrPath);
+
+      if (!SUCCEEDED(_lastResult)) {
+        return;
+      }
+
+      _dialogController.setFolder(ptrPath.value);
+    });
+  }
+
+  /// Sets the file name that is initially shown in the dialog.
+  void setFileName(String name) {
+    _dialogController.setFileName(name);
+  }
+
+  /// Sets the label of the confirmation button.
+  void setOkButtonLabel(String label) {
+    _dialogController.setOkButtonLabel(label);
+  }
+
+  /// Adds the given options to the dialog's current [options](https://pub.dev/documentation/win32/latest/winrt/FILEOPENDIALOGOPTIONS-class.html).
+  /// Both are bitfields.
+  void addOptions(int newOptions) {
+    using((Arena arena) {
+      final Pointer<Uint32> currentOptions = arena<Uint32>();
+      _lastResult = _dialogController.getOptions(currentOptions);
+      if (!SUCCEEDED(_lastResult)) {
+        return;
+      }
+      currentOptions.value |= newOptions;
+      _lastResult = _dialogController.setOptions(currentOptions.value);
+    });
+  }
+
+  /// Sets the filters for allowed file types to select.
+  /// filters -> std::optional<EncodableList>
+  void setFileTypeFilters(List<XTypeGroup> filters) {
+    final Map<String, String> filterSpecification = <String, String>{};
+
+    if (filters.isEmpty) {
+      filterSpecification[_allowAnyValue] = _allowAnyExtension;
+    } else {
+      for (final XTypeGroup option in filters) {
+        final String? label = option.label;
+        if (option.allowsAny || option.extensions!.isEmpty) {
+          filterSpecification[label ?? _allowAnyValue] = _allowAnyExtension;
+        } else {
+          final String extensionsForLabel = option.extensions!
+              .map((String extension) => '*.$extension')
+              .join(';');
+          filterSpecification[label ?? extensionsForLabel] = extensionsForLabel;
+        }
+      }
+    }
+
+    using((Arena arena) {
+      final Pointer<COMDLG_FILTERSPEC> registerFilterSpecification =
+          arena<COMDLG_FILTERSPEC>(filterSpecification.length);
+
+      int index = 0;
+      for (final String key in filterSpecification.keys) {
+        registerFilterSpecification[index]
+          ..pszName = TEXT(key)
+          ..pszSpec = TEXT(filterSpecification[key]!);
+        index++;
+      }
+
+      _lastResult = _dialogController.setFileTypes(
+          filterSpecification.length, registerFilterSpecification);
+    });
+  }
+
+  /// Displays the dialog, and returns the selected files, or null on error.
+  List<String?>? show(int parentWindow) {
+    _lastResult = _dialogController.show(parentWindow);
+    if (!SUCCEEDED(_lastResult)) {
+      return null;
+    }
+    late List<String>? files;
+
+    using((Arena arena) {
+      final Pointer<Pointer<COMObject>> shellItemArrayPtr =
+          arena<Pointer<COMObject>>();
+      final Pointer<Uint32> shellItemCountPtr = arena<Uint32>();
+      final Pointer<Pointer<COMObject>> shellItemPtr =
+          arena<Pointer<COMObject>>();
+
+      files =
+          _getFilePathList(shellItemArrayPtr, shellItemCountPtr, shellItemPtr);
+    });
+    return files;
+  }
+
+  List<String>? _getFilePathList(
+      Pointer<Pointer<COMObject>> shellItemArrayPtr,
+      Pointer<Uint32> shellItemCountPtr,
+      Pointer<Pointer<COMObject>> shellItemPtr) {
+    final List<String> files = <String>[];
+    if (_isOpenDialog) {
+      _lastResult = _dialogController.getResults(shellItemArrayPtr);
+      if (!SUCCEEDED(_lastResult)) {
+        return null;
+      }
+
+      final IShellItemArray shellItemResources =
+          IShellItemArray(shellItemArrayPtr.cast());
+      _lastResult = shellItemResources.getCount(shellItemCountPtr);
+      if (!SUCCEEDED(_lastResult)) {
+        return null;
+      }
+      for (int index = 0; index < shellItemCountPtr.value; index++) {
+        shellItemResources.getItemAt(index, shellItemPtr);
+        final IShellItem shellItem = IShellItem(shellItemPtr.cast());
+        files.add(_shellWin32Api.getPathForShellItem(shellItem));
+      }
+    } else {
+      _lastResult = _dialogController.getResult(shellItemPtr);
+      if (!SUCCEEDED(_lastResult)) {
+        return null;
+      }
+      final IShellItem shellItem = IShellItem(shellItemPtr.cast());
+      files.add(_shellWin32Api.getPathForShellItem(shellItem));
+    }
+    return files;
+  }
+}

packages/file_selector/file_selector_windows/lib/src/file_selector_dart/file_dialog_controller_factory.dart

@@ -0,0 +1,18 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:win32/win32.dart';
+
+import 'file_dialog_controller.dart';
+import 'ifile_dialog_controller_factory.dart';
+import 'ifile_open_dialog_factory.dart';
+
+/// Implementation of FileDialogControllerFactory that makes standard
+/// FileDialogController instances.
+class FileDialogControllerFactory implements IFileDialogControllerFactory {
+  @override
+  FileDialogController createController(IFileDialog dialog) {
+    return FileDialogController(dialog, IFileOpenDialogFactory());
+  }
+}

packages/file_selector/file_selector_windows/lib/src/file_selector_dart/ifile_dialog_controller_factory.dart

@@ -0,0 +1,14 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:win32/win32.dart';
+
+import 'file_dialog_controller.dart';
+
+/// Interface for creating FileDialogControllers, to allow for dependency
+/// injection.
+abstract class IFileDialogControllerFactory {
+  /// Returns a FileDialogController to interact with the given [IFileDialog].
+  FileDialogController createController(IFileDialog dialog);
+}

packages/file_selector/file_selector_windows/lib/src/file_selector_dart/ifile_dialog_factory.dart

@@ -0,0 +1,19 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:win32/win32.dart';
+
+import 'dialog_mode.dart';
+
+/// A factory for [IFileDialog] instances.
+class IFileDialogFactory {
+  /// Creates the corresponding IFileDialog instace. The caller is responsible of releasing the resource.
+  IFileDialog createInstace(DialogMode dialogMode) {
+    if (dialogMode == DialogMode.Open) {
+      return FileOpenDialog.createInstance();
+    }
+
+    return FileSaveDialog.createInstance();
+  }
+}

packages/file_selector/file_selector_windows/lib/src/file_selector_dart/shell_win32_api.dart

@@ -0,0 +1,36 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:ffi';
+
+import 'package:ffi/ffi.dart';
+import 'package:win32/win32.dart';
+
+/// A thin wrapper for Win32 platform specific Shell methods.
+///
+/// The only purpose of this class is to decouple specific Win32 Api call from the bussiness logic so it can be init tested in any environment.
+class ShellWin32Api {
+  /// Creates and [initializes](https://learn.microsoft.com/en-us/windows/win32/api/shobjidl_core/nf-shobjidl_core-shcreateitemfromparsingname) a Shell item object from a parsing name.
+  /// If the directory doesn't exist it will return an error result.
+  int createItemFromParsingName(String initialDirectory, Pointer<GUID> ptrGuid,
+      Pointer<Pointer<NativeType>> ptrPath) {
+    return SHCreateItemFromParsingName(
+        TEXT(initialDirectory), nullptr, ptrGuid, ptrPath);
+  }
+
+  /// Returns the path for [shellItem] as a UTF-8 string, or an empty string on
+  /// failure.
+  String getPathForShellItem(IShellItem shellItem) {
+    return using((Arena arena) {
+      final Pointer<Pointer<Utf16>> ptrPath = arena<Pointer<Utf16>>();
+
+      if (!SUCCEEDED(
+          shellItem.getDisplayName(SIGDN.SIGDN_FILESYSPATH, ptrPath.cast()))) {
+        return '';
+      }
+
+      return ptrPath.value.toDartString();
+    });
+  }
+}