将 Flutter module 集成到 Android 项目

Flutter can be embedded into your existing Android application piecemeal, as a source code Gradle subproject or as AARs.

The integration flow can be done using the Android Studio IDE with the Flutter plugin or manually.

Using Android Studio

The Android Studio IDE is a convenient way of integrating your Flutter module automatically. With Android Studio, you can co-edit both your Android code and your Flutter code in the same project. You can also continue to use your normal IntelliJ Flutter plugin functionalities such as Dart code completion, hot reload, and widget inspector.

Add-to-app flows with Android Studio are only supported on Android Studio 3.6 with version 42+ of the Flutter IntelliJ plugin. The Android Studio integration also only supports integrating using a source code Gradle subproject, rather than using AARs. See below for more details on the distinction.

Using the File > New > New Module... menu in Android Studio in your existing Android project, you can either create a new Flutter module to integrate, or select an existing Flutter module that was created previously.

If you create a new module, you can use a wizard to select the module name, location, and so on.

The Android Studio plugin automatically configures your Android project to add your Flutter module as a dependency, and your app is ready to build.

Your app now includes the Flutter module as a dependency. You can jump to the API usage documentations to follow the next steps.

Manual integration

To integrate a Flutter module with an existing Android app manually, without using Flutter’s Android Studio plugin, follow these steps:

Create a Flutter module

Let’s assume that you have an existing Android app at some/path/MyApp, and that you want your Flutter project as a sibling:

$ cd some/path/
$ flutter create -t module --org com.example my_flutter

This creates a some/path/my_flutter/ Flutter module project with some Dart code to get you started and a .android/ hidden subfolder. The .android folder contains an Android project that can both help you run a barebones standalone version of your Flutter module via flutter run and it’s also a wrapper that helps bootstrap the Flutter module an embeddable Android library.

Java 8 requirement

The Flutter Android engine uses Java 8 features.

Before attempting to connect your Flutter module project to your host Android app, ensure that your host Android app declares the following source compatibility within your app’s build.gradle file, under the android { } block, such as:

android {
  //...
  compileOptions {
    sourceCompatibility 1.8
    targetCompatibility 1.8
  }
}

Add the Flutter module as a dependency

Next, add the Flutter module as a dependency of your existing app in Gradle. There are two ways to achieve this. The AAR mechanism creates generic Android AARs as intermediaries that packages your Flutter module. This is good when your downstream app builders don’t want to have the Flutter SDK installed. But, it adds one more build step if you build frequently.

The source code subproject mechanism is a convenient one-click build process, but requires the Flutter SDK. This is the mechanism used by the Android Studio IDE plugin.

Option A - Depend on the Android Archive (AAR)

This option packages your Flutter library as a generic local Maven repository composed of AARs and POMs artifacts. This option allows your team to build the host app without installing the Flutter SDK. You can then distribute the artifacts from a local or remote repository.

Let’s assume you built a Flutter module at some/path/my_flutter, and then run:

$ cd some/path/my_flutter
$ flutter build aar

Then, follow the on-screen instructions to integrate.

More specifically, this command creates (by default all debug/profile/release modes) a local repository, with the following files:

build/host/outputs/repo
└── com
    └── example
        └── my_flutter
            ├── flutter_release
            │   ├── 1.0
            │   │   ├── flutter_release-1.0.aar
            │   │   ├── flutter_release-1.0.aar.md5
            │   │   ├── flutter_release-1.0.aar.sha1
            │   │   ├── flutter_release-1.0.pom
            │   │   ├── flutter_release-1.0.pom.md5
            │   │   └── flutter_release-1.0.pom.sha1
            │   ├── maven-metadata.xml
            │   ├── maven-metadata.xml.md5
            │   └── maven-metadata.xml.sha1
            ├── flutter_profile
            │   ├── ...
            └── flutter_debug
                └── ...

To depend on the AAR, the host app must be able to find these files.

To do that, edit app/build.gradle in your host app such as it includes the local repository and the dependency:

android {
  // ...
}

repositories {
  maven {
    url 'some/path/my_flutter/build/host/outputs/repo'
    // This is relative to the location of the build.gradle file
    // if using a relative path.
  }
  maven {
    url 'https://storage.googleapis.com/download.flutter.io'
  }
}

dependencies {
  // ...
  debugImplementation 'com.example.flutter_module:flutter_debug:1.0'
  profileImplementation 'com.example.flutter_module:flutter_profile:1.0'
  releaseImplementation 'com.example.flutter_module:flutter_release:1.0'
}

Your app now includes the Flutter module as a dependency. You can follow the next steps in the API usage documentations.

Option B - Depend on the module’s source code

This option enables a one-step build for both your Android project and Flutter project. This option is convenient when you work on both parts simultaneously and rapidly iterate, but your team must install the Flutter SDK to build the host app.

Include the Flutter module as a subproject in the host app’s settings.gradle:

include ':app'                                     // assumed existing content
setBinding(new Binding([gradle: this]))                                 // new
evaluate(new File(                                                      // new
  settingsDir.parentFile,                                               // new
  'my_flutter/.android/include_flutter.groovy'                          // new
))                                                                      // new

Assuming my_flutter is a sibling to MyApp.

The binding and script evaluation allows the Flutter module to include itself (as :flutter) and any Flutter plugins used by the module (as :package_info, :video_player, etc) in the evaluation context of your settings.gradle.

Introduce an implementation dependency on the Flutter module from your app:

dependencies {
  implementation project(':flutter')
}

Your app now includes the Flutter module as a dependency. You can follow the next steps in the API usage documentations.