Flutter Building Plugins

Developing Flutter Plugins

Contents

• Architecture & Design Patterns
• Workflow: Creating a New Plugin
• Workflow: Implementing Android Platform Code
• Workflow: Implementing Windows Platform Code
• Workflow: Adding Platforms to an Existing Plugin
• Examples

Architecture & Design Patterns

Federated Plugins

Implement federated plugins to split a plugin's API across multiple packages, allowing independent teams to build platform-specific implementations. Structure federated plugins into three distinct components:

1. App-facing interface: The primary package users depend on. It exports the public API.
2. Platform interface: The package defining the common interface that all platform implementations must implement.
3. Platform implementations: Independent packages containing platform-specific code (e.g., my_plugin_android, my_plugin_windows).

FFI vs. Standard Plugins

Choose the correct plugin template based on your native interoperability requirements:

• Standard Plugins (--template=plugin): Use for accessing platform-specific APIs (e.g., Android SDK, iOS frameworks) via Method Channels.
• FFI Plugins (--template=plugin_ffi): Use for accessing C/C++ native libraries, configuring Google Play services on Android, or using static linking on iOS/macOS.
  • Constraint: FFI plugin packages support bundling native code and method channel registration code, but not method channels themselves. If you require both method channels and FFI, use the standard non-FFI plugin template.

Workflow: Creating a New Plugin

Follow this workflow to initialize a new plugin package.

Task Progress:

• Determine if the plugin requires FFI or standard Method Channels.
• Execute the appropriate flutter create command.
• Verify the generated directory structure.

Conditional Initialization:

• If creating a STANDARD plugin: Run the following command, specifying your supported platforms, organization, and preferred languages (defaults are Swift and Kotlin):

  flutter create --template=plugin \
    --platforms=android,ios,web,linux,macos,windows \
    --org com.example.organization \
    -i objc -a java \
    my_plugin

• If creating an FFI plugin: Run the following command to generate a project with Dart code in lib (using dart:ffi) and native source code in src (with a CMakeLists.txt):

  flutter create --template=plugin_ffi my_ffi_plugin

Workflow: Implementing Android Platform Code

Always edit Android platform code using Android Studio to ensure proper code completion and Gradle synchronization.

Task Progress:

• Run initial build to generate necessary Gradle files.
• Open the Android module in Android Studio.
• Implement FlutterPlugin and lifecycle-aware interfaces.
• Refactor legacy registerWith logic.
• Run validator -> review errors -> fix.

1. Generate Build Files: Build the code at least once before editing to resolve dependencies.

   cd example
   flutter build apk --config-only

2. Open in IDE: Launch Android Studio and open the example/android/build.gradle or example/android/build.gradle.kts file.
3. Locate Source: Navigate to your plugin's source code at java/<organization-path>/<PluginName>.
4. Implement V2 Embedding:
   • Implement the FlutterPlugin interface.
   • Ensure your plugin class has a public constructor.
   • Extract shared initialization logic from the legacy registerWith() method and the new onAttachedToEngine() method into a single private method. Both entry points must call this private method to maintain backward compatibility without duplicating logic.
5. Implement Lifecycle Interfaces:
   • If your plugin requires an Activity reference: Implement the ActivityAware interface and handle the onAttachedToActivity, onDetachedFromActivityForConfigChanges, onReattachedToActivityForConfigChanges, and onDetachedFromActivity callbacks.
   • If your plugin runs in a background Service: Implement the ServiceAware interface.
6. Update Example App: Ensure the example app's MainActivity.java extends the v2 embedding io.flutter.embedding.android.FlutterActivity.
7. Document API: Document all non-overridden public members in your Android implementation.