Flutter 開發筆記 - 撰寫平台相依性功能，以取得 Android Device 資料為例

本文參考：docs.flutter.dev/development/platform-integration/platform-channels?tab=android-channel-kotlin-tab 做為練習，快速筆記。

研究了一下 Flutter 如何寫平台相依性的程式碼，看一眼也是常見的 Channel or Message 等溝通機制，也滿直觀的。以 Android 平台和 Kotlin 為例，先找到 MainActivity.kt ，接著，在 Code -> Override Methods 可以找到 configureFlutterEngine 可以添加

class MainActivity: FlutterActivity() {

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {

        super.configureFlutterEngine(flutterEngine)

    }

}

接著就可以在透過 MethodChannel 建立綁定溝通管道：

import android.os.Build

import io.flutter.embedding.android.FlutterActivity

import io.flutter.embedding.engine.FlutterEngine

import io.flutter.plugin.common.MethodChannel

class MainActivity: FlutterActivity() {

    private val myCHANNEL = "samples.flutter.dev/helper"

    

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {

        super.configureFlutterEngine(flutterEngine)

        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, myCHANNEL).setMethodCallHandler {

                call, result ->

            // This method is invoked on the main thread.

            // TODO

            if (call.method == "getBatteryLevel") {

                val batteryLevel = 0; // getBatteryLevel()

                if (batteryLevel != -1) {

                    result.success(batteryLevel)

                } else {

                    result.error("UNAVAILABLE", "Battery level not available.", null)

                }

            } else if (call.method == "getDeviceInfo") {

                result.success(getDeviceInfo())

            } else {

                result.notImplemented()

            }

        }

    }

    private fun getDeviceInfo(): HashMap<String, String> {

        val deviceInfo:HashMap<String, String> = HashMap<String, String>()

        deviceInfo.run {

            put("MODEL", Build.MODEL)

            put("MANUFACTURER", Build.MANUFACTURER)

        }

        return deviceInfo

    }

}

如此在 Flutter Dart 端，就可以呼叫：

class _MyHomePageState extends State<MyHomePage> {

  static const platform = MethodChannel('samples.flutter.dev/helper');

  String _deviceInfo = "system info unknown";

  Future<void> _getDeviceInfo() async {

    Map<String, String> deviceInfo = {};

    try {

      final Map<Object?, Object?> result = await platform.invokeMethod('getDeviceInfo');

      deviceInfo.clear();

      result.forEach((key, value) {

        if (key.runtimeType == String && value.runtimeType == String) {

          deviceInfo[key.toString()] = value.toString();

        }

      });

    } on PlatformException catch (e) {

      deviceInfo.clear();

    } on Exception catch (e) {

      //print("Exception catch: $e ");

    }

    setState(() {

      _deviceInfo = json.encode(deviceInfo);

    });

  }

...

後續就只是完善細節，強烈建議直接觀看官方文件，有完整的細流程資訊和各平台的範例： docs.flutter.dev/development/platform-integration/platform-channels