# Flutter Plugins

> Build a Flutter plugin that provides native interop for other Flutter apps to use

- Skill: `ulpi-io/flutter-plugins` (Agent Skill)
- Install (CLI): `npx skillmds@latest add ulpi-io/flutter-plugins`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ulpi-io/flutter-plugins/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: ulpi-io (https://skillmd.com/u/ulpi-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/ulpi-io/flutter-plugins

---

# flutter-plugin-generator

## Goal
Scaffolds and configures Flutter plugin packages, handling standard method channels, FFI integrations, and federated plugin architectures. It configures platform-specific native code environments, implements Android v2 embedding lifecycle interfaces, and establishes platform interface packages.

## Decision Logic

Use the following decision tree to determine the plugin architecture and template:

1. **Does the plugin require C/C++ native code via `dart:ffi`?**
   * **Yes:** Use `--template=plugin_ffi`.
     * *Note:* FFI plugins support bundling native code and method channel registration, but *not* method channels themselves.
   * **No:** Proceed to step 2.
2. **Does the plugin require BOTH `dart:ffi` and Method Channels?**
   * **Yes:** Use `--template=plugin` (Non-FFI). You must configure FFI manually within the standard plugin structure.
   * **No:** Proceed to step 3.
3. **Will the plugin be developed by multiple teams or require highly decoupled platform implementations?**
   * **Yes:** Implement a **Package-Separated Federated Plugin** (App-facing package, Platform Interface package, Platform Implementation packages).
   * **No:** Implement a standard monolithic plugin.

## Instructions

1. **Gather Plugin Requirements**
   **STOP AND ASK THE USER:**
   * What is the plugin name?
   * What is the organization name (reverse domain notation, e.g., `com.example`)?
   * Which platforms should be supported (comma-separated: `android,ios,web,linux,macos,windows`)?
   * Do you need an FFI plugin or a standard Method Channel plugin?
   * Do you prefer Java or Kotlin for Android? Objective-C or Swift for iOS?
   * Should this be a federated plugin?

2. **Generate the Plugin Package**
   Execute the Flutter CLI command based on the user's parameters. 
   
   *Standard Plugin Example:*
   ```bash
   flutter create --org com.example --template=plugin --platforms=android,ios,macos -a kotlin -i swift my_plugin
   ```
   
   *FFI Plugin Example:*
   ```bash
   flutter create --template=plugin_ffi my_ffi_plugin
   ```

3. **Configure Federated Plugin Architecture (If Applicable)**
   If the user requested a federated plugin, configure the `pubspec.yaml` of the app-facing package to endorse the platform implementations.

   ```yaml
   # App-facing pubspec.yaml
   flutter:
     plugin:
       platforms:
         android:
           default_package: my_plugin_android
         windows:
           default_package: my_plugin_windows

   dependencies:
     my_plugin_android: ^1.0.0
     my_plugin_windows: ^1.0.0
   ```

   For the platform implementation packages, define the `implements` key:
   ```yaml
   # Platform implementation pubspec.yaml (e.g., my_plugin_windows)
   flutter:
     plugin:
       implements: my_plugin
       platforms:
         windows:
           pluginClass: MyPlugin
   ```

4. **Prepare Native Environments for Editing**
   Before modifying native code, you MUST build the example app to resolve dependencies and generate necessary files.
   ```bash
   cd my_plugin/example
   flutter build apk --config-only # For Android
   flutter build ios --no-codesign --config-only # For iOS
   flutter build windows # For Windows
   ```

5. **Implement Android v2 Embedding Lifecycle**
   Modify the Android plugin class (e.g., `android/src/main/kotlin/com/example/my_plugin/MyPlugin.kt`). Extract logic from `registerWith()` into a private method shared with `onAttachedToEngine()`. Implement `ActivityAware` or `ServiceAware` if context is needed.

   ```kotlin
   package com.example.my_plugin

   import androidx.annotation.NonNull
   import io.flutter.embedding.engine.plugins.FlutterPlugin
   import io.flutter.embedding.engine.plugins.activity.ActivityAware
   import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding
   import io.flutter.plugin.common.MethodCall
   import io.flutter.plugin.common.MethodChannel
   import io.flutter.plugin.common.MethodChannel.MethodCallHandler
   import io.flutter.plugin.common.MethodChannel.Result

   class MyPlugin: FlutterPlugin, MethodCallHandler, ActivityAware {
     private lateinit var channel : MethodChannel

     override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
       setupChannel(flutterPluginBinding.binaryMessenger)
     }

     // Shared private method for v1 and v2 embedding compatibility
     private fun setupChannel(messenger: BinaryMessenger) {
       channel = MethodChannel(messenger, "my_plugin")
       channel.setMethodCallHandler(this)
     }

     override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {
       if (call.method == "getPlatformVersion") {
         result.success("Android ${android.os.Build.VERSION.RELEASE}")
       } else {
         result.notImplemented()
       }
     }

     override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {
       channel.setMethodCallHandler(null)
     }

     override fun onAttachedToActivity(binding: ActivityPluginBinding) {
       // Handle Activity attachment
     }

     override fun onDetachedFromActivityForConfigChanges() {}
     override fun onReattachedToActivityForConfigChanges(binding: ActivityPluginBinding) {}
     override fun onDetachedFromActivity() {}
   }
   ```

6. **Validate and Fix**
   Run the plugin tests and analyzer to ensure the generated code is valid.
   ```bash
   cd my_plugin
   flutter analyze
   flutter test
   ```
   *If the analyzer reports missing dependencies or unresolved native symbols, verify that step 4 (building the example app) was executed successfully. Fix any missing imports in the native code blocks.*

## Constraints

* **Never** attempt to use Method Channels inside a package created with `--template=plugin_ffi`. If both are required, use `--template=plugin`.
* **Always** build the example project (`flutter build <platform>`) at least once before attempting to edit or analyze native Android (`build.gradle`), iOS (`.xcworkspace`), or Windows (`.sln`) files.
* **Never** leave public members undocumented in the Dart API (`lib/<package_name>.dart`).
* **Always** use the v2 Android embedding (`FlutterPlugin`). Do not rely solely on the deprecated `PluginRegistry.Registrar`.
* **Never** edit the `.android` or `.ios` directories inside a Flutter module; only edit the native code inside the plugin's `android/` or `ios/` directories.