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Add-to-App Samples

This directory contains a bunch of Android and iOS projects (beginning android_ and ios_, respectively) that import and use one of several Flutter modules (which have names beginning with flutter_). They're designed to show recommended approaches for adding Flutter to existing Android and iOS apps.

Goals for these samples

Show developers how to add Flutter to their existing applications.
Show the following options:
- Whether to build the Flutter module from source each time the app builds or rely on a separately pre-built module.
- Whether plugins are needed by the Flutter module used in the app.
Show Flutter being integrated ergonomically with applications with existing middleware and business logic data classes.

tl;dr

If you're just looking to get up and running quickly, these bash commands will fetch packages and set up dependencies (note that the above commands assume you're building for both iOS and Android, with both toolchains installed):

  #!/bin/bash
  set -e

  cd flutter_module_using_plugin
  flutter pub get
  cd ../flutter_module_books
  flutter pub get
  cd ../flutter_module
  flutter pub get

  # For Android builds:
  flutter build aar

  # For iOS builds:
  flutter build ios-framework --xcframework --output=../ios_using_prebuilt_module/Flutter
  cd ../ios_fullscreen
  pod install
  cd ../ios_using_plugin
  pod install

Once those commands have run, you can go into any of the app directories (the ones beginning android_ or ios_), and build the apps as you normally would.

Installing Cocoapods

The iOS samples in this repo require the latest version of Cocoapods. To make sure you've got it, run the following command on a macOS machine:

sudo gem install cocoapods

See https://guides.cocoapods.org/using/getting-started.html for more details.

The important bits

Flutter modules

There are three Flutter modules included in the codebase:

flutter_module displays the dimensions of the screen, a button that increments a simple counter, and an optional exit button.
flutter_module_using_plugin does everything flutter_module does and adds another button that will open the Flutter documentation in a browser using the url_launcher Flutter plugin.
flutter_module_books simulates an integration scenario with existing platform business logic and middleware. It uses the pigeon plugin to make integration easier by generating the platform channel interop inside wrapper API and data classes that are shared between the platform and Flutter.

Before using them, you need to resolve the Flutter modules' dependencies. Do so by running this command from within the flutter_module, flutter_module_using_plugin, and flutter_module_books directories:

flutter pub get

Android and iOS applications

In addition to the Flutter modules, this repo also includes a number of Android and iOS applications that demonstrate different ways of importing them.

With the exception of android_using_prebuilt_module, the Android apps are ready to run once you've completed the flutter pub get commands listed above. Two of the iOS apps (ios_fullscreen and ios_using_plugin) use Cocoapods, though, so you need to run this command within their project directories to install their dependencies:

pod install

Once that command is complete, you'll find an xcworkspace file in the project directories with the correct Flutter module (and any other dependencies) included. Open that workspace file, and the app is ready to build and run.

`android_fullscreen` and `ios_fullscreen`

These apps showcase a relatively straightforward integration of flutter_module:

The Flutter module is built along with the app when the app is built.
The Flutter engine is warmed up at app launch.
The Flutter view is presented with a full-screen Activity or UIViewController.
The Flutter view is a navigational leaf node; it does not launch any new, native Activities or UIViewControllers in response to user actions.

If you are new to Flutter's add-to-app APIs, these projects are a great place to begin learning how to use them.

`android_using_plugin` and `ios_plugin`

These apps are similar to android_fullscreen and ios_fullscreen, with the following differences:

Rather than importing flutter_module, they import flutter_module_using_plugin.
They include the native code (Kotlin or Swift) required to initialize plugins at Flutter engine creation time.
Their Flutter view includes an additional button that opens the Flutter docs in the mobile device's browser.

If you're interested in learning what additional steps an app needs to take in order to use a Flutter module that relies on plugins, these projects can help.

`android_using_prebuilt_module` and `ios_using_prebuilt_module`

These apps are essentially identical to android_fullscreen and ios_fullscreen, respectively, with one key difference. Rather than being set up to compile the flutter_module from source each time the app is built, they import a the module as a prebuilt aar (Android) or framework (iOS). This can be useful for teams that don't want to require every developer working on the app to have the Flutter toolchain installed on their local machines.

Prior to building either project for the first time, the flutter_module needs to be built.

Building for android_using_prebuilt_module

To build flutter_module as an aar, run this command from the flutter_module directory:

flutter build aar

It will produce aar files for debug, profile, and release mode. The Android app is configured to import the appropriate aar based on its own build configuration, so if you build a debug version of the app, it will look for the debug aar, and so on.

If the flutter_module project is updated, the aar files must be rebuilt via one of the commands above in order for those changes to appear in the app.

Building for ios_using_prebuilt_module

To build flutter_module as a set of frameworks, run this command from the flutter_module directory:

flutter build ios-framework --xcframework --output=../ios_using_prebuilt_module/Flutter

This will output frameworks for debug, profile, and release modes into ios_using_prebuilt_module/Flutter. The project file for ios_using_prebuilt_module has been configured to find the frameworks there.

For more information on how to modify an existing iOS app to reference prebuilt Flutter frameworks, see this article in the Flutter GitHub wiki:

https://flutter.dev/docs/development/add-to-app/ios/project-setup

`android_books` and `ios_books (TODO)`

These apps integrate the flutter_books module using the simpler build-together project setup. They simulate a mock scenario where an existing book catalog list app already exists. Flutter is used to implement an additional book details page.

Similar to android_fullscreen and ios_fullscreen.
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.
- iOS TODO.
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.
- iOS TODO.
The 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. No manual platform channel plumbing needed for interop.
- The api.dart/java/mm files generated from the flutter_module_books/pigeon/schema.dart file are checked into source control. Therefore pigeon is only a dev dependency with no runtime requirements.
- If the schema.dart is modified, the generated classes can be updated with
```
flutter pub run pigeon \
    --input pigeon/schema.dart \
    --java_out ../android_books/app/src/main/java/dev/flutter/example/books/Api.java \
    --java_package "dev.flutter.example.books"
```
  in the flutter_module_books directory.

Once you've understood the basics of add-to-app with android_fullscreen and ios_fullscreen, this is a good sample to demonstrate how to integrate Flutter in a slightly more realistic setting with existing business logic.

Questions/issues

If you have a general question about incorporating Flutter into an existing iOS or Android app, the best places to go are:

If you run into an issue with the sample itself, please file an issue in the main Flutter repo.

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