Flutter创建插件的步骤

说明

Flutter插件是一种用于封装平台特定代码的组件，它通过方法通道（Method Channel） 将Dart代码与平台（如Android和iOS）代码连接起来。插件可以使Flutter应用访问原生平台的功能，如相机、地理位置、蓝牙等。

开发插件的步骤：

1. 定义插件Dart API
2. 编写原生平台代码
3. 连接Dart与原生平台

另外：

联合插件：将原生平台代码拆分为单独的包，并组合到主插件包中，参考：Federated plugins

共享iOS与macOS平台的代码：要在插件中共享iOS与macOS平台的代码，参考：Shared iOS and macOS implementations

下面讨论开发插件的步骤。

创建项目

创建一个名为hello的插件，支持Android、iOS：

flutter create --template plugin --platforms android,ios --project-name hello --org com.example hello-plugin

项目结构：

hello_plugin/
├── android/
│   └── src/...               # Android平台代码
├── example/                  # 示例项目，它把外层的插件项目当作依赖，用于测试与演示。
├── ios/
│   └── Classes/...           # iOS平台代码
├── lib/
│   └── hello.dart            # Dart接口，插件的API
├── pubspec.yaml              # 包配置

主要代码：

pubspec.yaml

name: hello
description: "A new Flutter plugin project."
version: 0.0.1
homepage:

environment:
  sdk: ^3.5.3
  flutter: '>=3.3.0'

dependencies:
  flutter:
    sdk: flutter
  plugin_platform_interface: ^2.0.2

dev_dependencies:
  flutter_test:
    sdk: flutter
  flutter_lints: ^4.0.0

flutter:
  plugin:
    platforms:
      android:
        package: com.example.hello
        pluginClass: HelloPlugin
      ios:
        pluginClass: HelloPlugin

hello.dart

import 'hello_platform_interface.dart';

class Hello {
  Future<String?> getPlatformVersion() {
    return HelloPlatform.instance.getPlatformVersion();
  }
}

HelloPlugin.kt

package com.example.hello

import androidx.annotation.NonNull

import io.flutter.embedding.engine.plugins.FlutterPlugin
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

/** HelloPlugin */
class HelloPlugin: FlutterPlugin, MethodCallHandler {
  /// The MethodChannel that will the communication between Flutter and native Android
  ///
  /// This local reference serves to register the plugin with the Flutter Engine and unregister it
  /// when the Flutter Engine is detached from the Activity
  private lateinit var channel : MethodChannel

  override fun onAttachedToEngine(flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
    channel = MethodChannel(flutterPluginBinding.binaryMessenger, "hello")
    channel.setMethodCallHandler(this)
  }

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

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

HelloPlugin.swift

import Flutter
import UIKit

public class HelloPlugin: NSObject, FlutterPlugin {
  public static func register(with registrar: FlutterPluginRegistrar) {
    let channel = FlutterMethodChannel(name: "hello", binaryMessenger: registrar.messenger())
    let instance = HelloPlugin()
    registrar.addMethodCallDelegate(instance, channel: channel)
  }

  public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
    switch call.method {
    case "getPlatformVersion":
      result("iOS " + UIDevice.current.systemVersion)
    default:
      result(FlutterMethodNotImplemented)
    }
  }
}

实现

创建的项目中，已包含简单的实现代码，下面说明一下：

定义插件API

编辑lib/hello.dart，定义API。

在lib/hello.dart中，默认定义了一个getPlatformVersion方法。

实现Android平台

编译example

为了顺利打开项目，先编译一次hello/example项目：

flutter build apk --config-only

打开example

1. 编译后，使用Android Studio打开hello/example/android/build.gradle。

   WARNING

   是打开示例项目hello/example/android/build.gradle，不是外层的hello/android/build.gradle！

2. 打开后，进行Gradle Sync。

实现API

编辑HelloPlugin.kt，实现API。

实现iOS平台

编译example

为了顺利打开项目，先编译一次hello/example项目：

flutter build ios --no-codesign --config-only

打开example

编译后，使用XCode打开hello/example/ios/Runner.xcworkspace。

实现API

编辑HelloPlugin.swift。

如果要添加CocoaPod依赖，参考：Add CocoaPod dependencies

连接Dart与平台代码

连接的原理是Method Channel。

在lib/hello.dart中，已有默认代码。

记录

Android

获取ApplicationContext

override fun onAttachedToEngine(flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
  val context = flutterPluginBinding.applicationContext
}

获取Activity

class HelloPlugin : FlutterPlugin, ActivityAware {

  private var activity: Activity? = null
  override fun onAttachedToActivity(binding: ActivityPluginBinding) {
    activity = binding.activity
  }

  override fun onDetachedFromActivityForConfigChanges() {
    activity = null
  }

  override fun onReattachedToActivityForConfigChanges(binding: ActivityPluginBinding) {
    activity = binding.activity
  }

  override fun onDetachedFromActivity() {
    activity = null
  }
}

iOS

获取UIViewController

let viewController = UIApplication.shared.keyWindow?.rootViewController

参考

官方文档：Developing plugin packages