Day13 开发套件 - 范例程序码介绍02 Android 端

接着来看Native 端（Android）：

预设建立的android/.../BatterylevelPlugin.kt：

class BatterylevelPlugin: 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(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
    channel = MethodChannel(flutterPluginBinding.binaryMessenger, "batterylevel")
    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)
  }
}

这边用来实现Native 端（Android）的功能，首先会实作**FlutterPlugin与MethodCallHandler**接口

1. 实作FlutterPlugin接口，必须实作onAttachedToEngine以及onDetachedFromEngine方法
   • onAttachedToEngine：插件被FlutterEngine加载时调用，可以做一些初始化工作，预设已在这边设置好MethodChannel的通道名称（需要与Flutter 端使用的MethodChannel名称相对应），并通过MethodChannel呼叫setMethodCallHandler来注册一个MessageHandler来接收此通道讯息，设定为this是因为BatterylevelPlugin已实作MethodCallHandler接口，所以能够处理接收通道的讯息
   • onDetachedFromEngine：插件从FlutterEngine移除时调用，可以做一些清理工作，这边对MethodChannel呼叫setMethodCallHandler设定为null，将此通道进行注销
2. 实作MethodCallHandler接口，就必须实作onMethodCall，目的可让MethodChannel调用setMethodCallHandler，实现从Flutter 端要调用的原生方法，这边对Flutter 端呼叫的方法getPlatformVersion做功能的实现，当Flutter 端呼叫此方法，就会回传现在Android 的版本资讯回去