snapshot of https://github.com/flutter/samples.git (main, 2026-09-16; blobs > 131072B omitted)

add_to_app/books/flutter_module_books/.gitignore

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+.DS_Store
+.dart_tool/
+
+.packages
+.pub/
+
+.idea/
+.vagrant/
+.sconsign.dblite
+.svn/
+
+*.swp
+profile
+
+DerivedData/
+
+.generated/
+
+*.pbxuser
+*.mode1v3
+*.mode2v3
+*.perspectivev3
+
+!default.pbxuser
+!default.mode1v3
+!default.mode2v3
+!default.perspectivev3
+
+xcuserdata
+
+*.moved-aside
+
+*.pyc
+*sync/
+Icon?
+.tags*
+
+build/
+.android/
+.ios/
+.flutter-plugins
+.flutter-plugins-dependencies
+
+# Symbolication related
+app.*.symbols
+
+# Obfuscation related
+app.*.map.json

add_to_app/books/flutter_module_books/.metadata

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+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: c0091b289e9966b6da99647b2f18dcb93de1f207
+  channel: master
+
+project_type: module

add_to_app/books/flutter_module_books/README.md

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+# Books add-to-app sample
+
+This application simulates a mock scenario in which an existing app with
+business logic and middleware already exists. It demonstrates how to add Flutter
+to an app that has established patterns for these domains. For more information
+on how to use it, see the [README.md](../README.md) parent directory.
+
+This application also utilizes the [Pigeon](https://pub.dev/packages/pigeon)
+plugin to avoid manual platform channel wiring. Pigeon autogenerates the
+platform channel code in Dart/Java/Objective-C to allow interop using higher
+order functions and data classes instead of string-encoded methods and
+serialized primitives.
+
+The Pigeon autogenerated code is checked-in and ready to use. If the schema
+in `pigeon/schema.dart` is updated, the generated classes can also be re-
+generated using:
+
+```shell
+dart run pigeon --input pigeon/schema.dart \
+  --dart_out lib/api.dart \
+  --objc_header_out ../ios_books/IosBooks/api.h \
+  --objc_source_out ../ios_books/IosBooks/api.m \
+  --objc_prefix BK \
+  --java_out ../android_books/app/src/main/java/dev/flutter/example/books/Api.java \
+  --java_package "dev.flutter.example.books"
+```
+
+## Demonstrated concepts
+
+* An existing books catalog app is already implemented in Kotlin and Swift.
+* The platform-side app has existing middleware constraints that should also
+  be the middleware foundation for the additional Flutter screen.
+    * On Android, the Kotlin app already uses GSON and OkHttp for networking and
+      references the Google Books API as a data source. These same libraries
+      also underpin the data fetched and shown in the Flutter screen.
+* The platform application interfaces with the Flutter book details page using
+  idiomatic platform API conventions rather than Flutter conventions.
+    * On Android, the Flutter activity receives the book to show via activity
+      intent and returns the edited book by setting the result intent on the
+      activity. No Flutter concepts are leaked into the consumer activity.
+* The [pigeon](https://pub.dev/packages/pigeon) plugin is used to generate
+  interop APIs and data classes. The same `Book` model class is used within the
+  Kotlin/Swift program, the Dart program and in the interop between Kotlin/Swift
+  and Dart.
+
+## More info
+
+For more information about Flutter, check out
+[flutter.dev](https://flutter.dev).
+
+For instructions on how to integrate Flutter modules into your existing
+applications, see Flutter's
+[add-to-app documentation](https://flutter.dev/docs/development/add-to-app).

add_to_app/books/flutter_module_books/analysis_options.yaml

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+include: ../../../analysis_options.yaml

add_to_app/books/flutter_module_books/lib/api.dart

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+// Autogenerated from Pigeon (v1.0.1), do not edit directly.
+// See also: https://pub.dev/packages/pigeon
+// ignore_for_file: public_member_api_docs, non_constant_identifier_names, avoid_as, unused_import, unnecessary_parenthesis, prefer_null_aware_operators, omit_local_variable_types, unused_shown_name
+// @dart = 2.12
+import 'dart:async';
+import 'dart:typed_data' show Uint8List, Int32List, Int64List, Float64List;
+
+import 'package:flutter/services.dart';
+
+class Book {
+  String? title;
+  String? subtitle;
+  String? author;
+  String? summary;
+  String? publishDate;
+  int? pageCount;
+  Thumbnail? thumbnail;
+
+  Object encode() {
+    final pigeonMap = <Object?, Object?>{};
+    pigeonMap['title'] = title;
+    pigeonMap['subtitle'] = subtitle;
+    pigeonMap['author'] = author;
+    pigeonMap['summary'] = summary;
+    pigeonMap['publishDate'] = publishDate;
+    pigeonMap['pageCount'] = pageCount;
+    pigeonMap['thumbnail'] = thumbnail == null ? null : thumbnail!.encode();
+    return pigeonMap;
+  }
+
+  static Book decode(Object message) {
+    final pigeonMap = message as Map<Object?, Object?>;
+    return Book()
+      ..title = pigeonMap['title'] as String?
+      ..subtitle = pigeonMap['subtitle'] as String?
+      ..author = pigeonMap['author'] as String?
+      ..summary = pigeonMap['summary'] as String?
+      ..publishDate = pigeonMap['publishDate'] as String?
+      ..pageCount = pigeonMap['pageCount'] as int?
+      ..thumbnail = pigeonMap['thumbnail'] != null
+          ? Thumbnail.decode(pigeonMap['thumbnail']!)
+          : null;
+  }
+}
+
+class Thumbnail {
+  String? url;
+
+  Object encode() {
+    final pigeonMap = <Object?, Object?>{};
+    pigeonMap['url'] = url;
+    return pigeonMap;
+  }
+
+  static Thumbnail decode(Object message) {
+    final pigeonMap = message as Map<Object?, Object?>;
+    return Thumbnail()..url = pigeonMap['url'] as String?;
+  }
+}
+
+class _FlutterBookApiCodec extends StandardMessageCodec {
+  const _FlutterBookApiCodec();
+  @override
+  void writeValue(WriteBuffer buffer, Object? value) {
+    if (value is Book) {
+      buffer.putUint8(128);
+      writeValue(buffer, value.encode());
+    } else {
+      super.writeValue(buffer, value);
+    }
+  }
+
+  @override
+  Object? readValueOfType(int type, ReadBuffer buffer) {
+    switch (type) {
+      case 128:
+        return Book.decode(readValue(buffer)!);
+
+      default:
+        return super.readValueOfType(type, buffer);
+    }
+  }
+}
+
+abstract class FlutterBookApi {
+  static const MessageCodec<Object?> codec = _FlutterBookApiCodec();
+
+  void displayBookDetails(Book book);
+  static void setup(FlutterBookApi? api) {
+    {
+      const channel = BasicMessageChannel<Object?>(
+          'dev.flutter.pigeon.FlutterBookApi.displayBookDetails', codec);
+      if (api == null) {
+        channel.setMessageHandler(null);
+      } else {
+        // ignore: avoid_types_on_closure_parameters
+        channel.setMessageHandler((Object? message) async {
+          assert(message != null,
+              'Argument for dev.flutter.pigeon.FlutterBookApi.displayBookDetails was null.');
+          final List<Object?> args = (message as List<Object?>?)!;
+          final Book? arg_book = args[0] as Book?;
+          assert(arg_book != null,
+              'Argument for dev.flutter.pigeon.FlutterBookApi.displayBookDetails was null, expected non-null Book.');
+          api.displayBookDetails(arg_book!);
+          return;
+        });
+      }
+    }
+  }
+}
+
+class _HostBookApiCodec extends StandardMessageCodec {
+  const _HostBookApiCodec();
+  @override
+  void writeValue(WriteBuffer buffer, Object? value) {
+    if (value is Book) {
+      buffer.putUint8(128);
+      writeValue(buffer, value.encode());
+    } else {
+      super.writeValue(buffer, value);
+    }
+  }
+
+  @override
+  Object? readValueOfType(int type, ReadBuffer buffer) {
+    switch (type) {
+      case 128:
+        return Book.decode(readValue(buffer)!);
+
+      default:
+        return super.readValueOfType(type, buffer);
+    }
+  }
+}
+
+class HostBookApi {
+  /// Constructor for [HostBookApi].  The [binaryMessenger] named argument is
+  /// available for dependency injection.  If it is left null, the default
+  /// BinaryMessenger will be used which routes to the host platform.
+  HostBookApi({BinaryMessenger? binaryMessenger})
+      : _binaryMessenger = binaryMessenger;
+
+  final BinaryMessenger? _binaryMessenger;
+
+  static const MessageCodec<Object?> codec = _HostBookApiCodec();
+
+  Future<void> cancel() async {
+    final channel = BasicMessageChannel<Object?>(
+        'dev.flutter.pigeon.HostBookApi.cancel', codec,
+        binaryMessenger: _binaryMessenger);
+    final Map<Object?, Object?>? replyMap =
+        await channel.send(null) as Map<Object?, Object?>?;
+    if (replyMap == null) {
+      throw PlatformException(
+        code: 'channel-error',
+        message: 'Unable to establish connection on channel.',
+        details: null,
+      );
+    } else if (replyMap['error'] != null) {
+      final error = (replyMap['error'] as Map<Object?, Object?>?)!;
+      throw PlatformException(
+        code: (error['code'] as String?)!,
+        message: error['message'] as String?,
+        details: error['details'],
+      );
+    }
+  }
+
+  Future<void> finishEditingBook(Book arg_book) async {
+    final BasicMessageChannel<Object?> channel = BasicMessageChannel<Object?>(
+        'dev.flutter.pigeon.HostBookApi.finishEditingBook', codec,
+        binaryMessenger: _binaryMessenger);
+    final Map<Object?, Object?>? replyMap =
+        await channel.send(<Object>[arg_book]) as Map<Object?, Object?>?;
+    if (replyMap == null) {
+      throw PlatformException(
+        code: 'channel-error',
+        message: 'Unable to establish connection on channel.',
+        details: null,
+      );
+    } else if (replyMap['error'] != null) {
+      final Map<Object?, Object?> error =
+          (replyMap['error'] as Map<Object?, Object?>?)!;
+      throw PlatformException(
+        code: (error['code'] as String?)!,
+        message: error['message'] as String?,
+        details: error['details'],
+      );
+    }
+  }
+}

add_to_app/books/flutter_module_books/lib/main.dart

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+// Copyright 2020 The Flutter team. 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:flutter/material.dart';
+import 'package:flutter_module_books/api.dart';
+
+void main() => runApp(const MyApp());
+
+class MyApp extends StatelessWidget {
+  const MyApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      theme: ThemeData(primaryColor: const Color(0xff6200ee)),
+      home: const BookDetail(),
+    );
+  }
+}
+
+typedef BookReceived = void Function(Book book);
+
+class FlutterBookApiHandler extends FlutterBookApi {
+  FlutterBookApiHandler(this.callback);
+
+  final BookReceived callback;
+
+  @override
+  void displayBookDetails(Book book) {
+    callback(book);
+  }
+}
+
+class BookDetail extends StatefulWidget {
+  const BookDetail({super.key, this.hostApi, this.flutterApi, this.book});
+
+  // These are the outgoing and incoming APIs that are here for injection for
+  // tests.
+  final HostBookApi? hostApi;
+  final FlutterBookApi? flutterApi;
+  final Book? book;
+
+  @override
+  State<BookDetail> createState() => _BookDetailState();
+}
+
+class _BookDetailState extends State<BookDetail> {
+  Book? book;
+
+  late HostBookApi hostApi;
+
+  FocusNode textFocusNode = FocusNode();
+  TextEditingController titleTextController = TextEditingController();
+  TextEditingController subtitleTextController = TextEditingController();
+  TextEditingController authorTextController = TextEditingController();
+
+  @override
+  void initState() {
+    super.initState();
+    book = widget.book;
+
+    // This `HostBookApi` class instance lets us make outgoing calls to the
+    // platform.
+    hostApi = widget.hostApi ?? HostBookApi();
+
+    // Registering this `FlutterBookApiHandler` class lets us receive incoming
+    // calls from the platform.
+    FlutterBookApi.setup(
+      FlutterBookApiHandler(
+        // The `FlutterBookApi` just has one method. Just give a closure for that
+        // method to the handler class.
+        (book) {
+          setState(() {
+            // This book model is what we're going to return to Kotlin eventually.
+            // Keep it bound to the UI.
+            this.book = book;
+            titleTextController.text = book.title ?? '';
+            titleTextController.addListener(() {
+              this.book!.title = titleTextController.text;
+            });
+            // Subtitle could be null.
+            subtitleTextController.text = book.subtitle ?? '';
+            subtitleTextController.addListener(() {
+              this.book!.subtitle = subtitleTextController.text;
+            });
+            authorTextController.text = book.author ?? '';
+            authorTextController.addListener(() {
+              this.book!.author = authorTextController.text;
+            });
+          });
+        },
+      ),
+    );
+  }
+
+  // Not overriding didUpdateWidget because the Android program can't change
+  // the book given to Flutter on the Android side.
+
+  void clear() {
+    book = null;
+    // Keep focus if going to the home screen but unfocus if leaving
+    // the activity.
+    textFocusNode.unfocus();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Book Details'),
+        leading: IconButton(
+          icon: const Icon(Icons.clear),
+          // Pressing clear cancels the edit and leaves the activity without
+          // modification.
+          onPressed: () {
+            hostApi.cancel();
+            clear();
+          },
+        ),
+        actions: [
+          IconButton(
+            icon: const Icon(Icons.check),
+            // Pressing save sends the updated book to the platform.
+            onPressed: book != null
+                ? () {
+                    hostApi.finishEditingBook(book!);
+                    clear();
+                  }
+                : null,
+          ),
+        ],
+      ),
+      body: book == null
+          // Draw a spinner until the platform gives us the book to show details
+          // for.
+          ? const Center(child: CircularProgressIndicator())
+          : BookForm(
+              book: book!,
+              focusNode: textFocusNode,
+              authorTextController: authorTextController,
+              subtitleTextController: subtitleTextController,
+              titleTextController: titleTextController,
+            ),
+    );
+  }
+}
+
+class BookForm extends StatelessWidget {
+  const BookForm({
+    super.key,
+    required this.book,
+    required this.focusNode,
+    required this.authorTextController,
+    required this.subtitleTextController,
+    required this.titleTextController,
+  });
+
+  final Book book;
+  final FocusNode focusNode;
+  final TextEditingController titleTextController;
+  final TextEditingController subtitleTextController;
+  final TextEditingController authorTextController;
+
+  @override
+  Widget build(BuildContext context) {
+    return Focus(
+      focusNode: focusNode,
+      child: ListView(
+        padding: const EdgeInsets.all(24),
+        children: [
+          TextField(
+            controller: titleTextController,
+            decoration: const InputDecoration(
+              border: OutlineInputBorder(),
+              filled: true,
+              hintText: "Title",
+              labelText: "Title",
+            ),
+          ),
+          const SizedBox(height: 24),
+          TextField(
+            controller: subtitleTextController,
+            maxLines: 2,
+            decoration: const InputDecoration(
+              border: OutlineInputBorder(),
+              filled: true,
+              hintText: "Subtitle",
+              labelText: "Subtitle",
+            ),
+          ),
+          const SizedBox(height: 24),
+          TextField(
+            controller: authorTextController,
+            decoration: const InputDecoration(
+              border: OutlineInputBorder(),
+              filled: true,
+              hintText: "Author",
+              labelText: "Author",
+            ),
+          ),
+          const SizedBox(height: 32),
+          const Divider(),
+          Center(
+            child: Padding(
+              padding: const EdgeInsets.all(8.0),
+              child: Text(
+                '${book.pageCount} pages  ~  published ${book.publishDate}',
+              ),
+            ),
+          ),
+          const Divider(),
+          const SizedBox(height: 32),
+          if (book.thumbnail?.url != null) ...[
+            Center(child: Image.network(book.thumbnail!.url!)),
+            const SizedBox(height: 32),
+          ],
+          if (book.summary != null) ...[
+            const Center(
+              child: Text(
+                'BOOK DESCRIPTION',
+                style: TextStyle(
+                  fontSize: 15,
+                  fontWeight: FontWeight.bold,
+                  decoration: TextDecoration.underline,
+                ),
+              ),
+            ),
+            const SizedBox(height: 12),
+            Text(
+              book.summary ?? '',
+              style: TextStyle(color: Colors.grey.shade600, height: 1.24),
+            ),
+          ],
+        ],
+      ),
+    );
+  }
+}

add_to_app/books/flutter_module_books/pigeon/schema.dart

@@ -0,0 +1,30 @@
+// Copyright 2020 The Flutter team. 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:pigeon/pigeon.dart';
+
+class Book {
+  String? title;
+  String? subtitle;
+  String? author;
+  String? summary;
+  String? publishDate;
+  int? pageCount;
+  Thumbnail? thumbnail;
+}
+
+class Thumbnail {
+  String? url;
+}
+
+@FlutterApi()
+abstract class FlutterBookApi {
+  void displayBookDetails(Book book);
+}
+
+@HostApi()
+abstract class HostBookApi {
+  void cancel();
+  void finishEditingBook(Book book);
+}

add_to_app/books/flutter_module_books/pubspec.yaml

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+name: flutter_module_books
+description: A Flutter module using the Pigeon package to demonstrate
+  integrating Flutter in a realistic scenario where the existing platform app
+  already has business logic and middleware constraints.
+version: 1.0.0+1
+resolution: workspace
+
+environment:
+  sdk: ^3.9.0-0
+
+dependencies:
+  flutter:
+    sdk: flutter
+
+dev_dependencies:
+  analysis_defaults:
+    path: ../../../analysis_defaults
+  pigeon: ">=11.0.0 <27.0.0"
+  flutter_test:
+    sdk: flutter
+
+flutter:
+  uses-material-design: true
+
+  # This section identifies your Flutter project as a module meant for
+  # embedding in a native host app.  These identifiers should _not_ ordinarily
+  # be changed after generation - they are used to ensure that the tooling can
+  # maintain consistency when adding or modifying assets and plugins.
+  # They also do not have any bearing on your native host application's
+  # identifiers, which may be completely independent or the same as these.
+  module:
+    androidX: true
+    androidPackage: dev.flutter.example.flutter_module_books
+    iosBundleIdentifier: dev.flutter.example.flutterModuleBooks

add_to_app/books/flutter_module_books/run_pigeon.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+dart run pigeon --input pigeon/schema.dart \
+  --dart_out lib/api.dart \
+  --objc_header_out ../ios_books/IosBooks/api.h \
+  --objc_source_out ../ios_books/IosBooks/api.m \
+  --objc_prefix BK \
+  --java_out ../android_books/app/src/main/java/dev/flutter/example/books/Api.java \
+  --java_package "dev.flutter.example.books"

add_to_app/books/flutter_module_books/test/widget_test.dart

@@ -0,0 +1,54 @@
+// Copyright 2020 The Flutter team. 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:flutter/material.dart';
+import 'package:flutter_module_books/api.dart';
+import 'package:flutter_module_books/main.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Pressing clear calls the cancel API', (tester) async {
+    MockHostBookApi mockHostApi = MockHostBookApi();
+
+    await tester.pumpWidget(
+      MaterialApp(home: BookDetail(hostApi: mockHostApi)),
+    );
+
+    await tester.tap(find.byIcon(Icons.clear));
+
+    expect(mockHostApi.cancelCalls, 1);
+  });
+
+  testWidgets('Pressing done calls the finish editing API', (
+    tester,
+  ) async {
+    MockHostBookApi mockHostApi = MockHostBookApi();
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: BookDetail(book: Book(), hostApi: mockHostApi),
+      ),
+    );
+
+    await tester.tap(find.byIcon(Icons.check));
+
+    expect(mockHostApi.booksFinished.length, 1);
+  });
+}
+
+// A super-simple mock for testing that calls are made to the API.
+class MockHostBookApi implements HostBookApi {
+  int cancelCalls = 0;
+  final booksFinished = <Book>[];
+
+  @override
+  Future<void> cancel() async {
+    cancelCalls++;
+  }
+
+  @override
+  Future<void> finishEditingBook(Book arg) async {
+    booksFinished.add(arg);
+  }
+}