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 

Flutter 開發筆記 - 排除 Could not open settings generic class cache for settings file @ macOS 13.2.1, openjdk 19.0.2, Android Studio Electric Eel | 2022.1.1 Patch 2

最近工作上關係，來回顧一下 Flutter app 的開發，預計寫一款非常簡單的 App 試試水溫。結果在 macOS 13.2.1, openjdk 19.0.2, Android Studio Electric Eel | 2022.1.1 Patch 2 環境，預設弄個專案出來卻不能編譯：

Launching lib/main.dart on sdk gphone64 arm64 in debug mode...

Running Gradle task 'assembleDebug'...

FAILURE: Build failed with an exception.

* What went wrong:

Could not open settings generic class cache for settings file '/Users/UserID/AndroidStudio/usb_displayport_helper/android/settings.gradle' (/Users/UserID/.gradle/caches/7.5/scripts/XXXXXX).

> BUG! exception in phase 'semantic analysis' in source unit '_BuildScript_' Unsupported class file major version 63

* Try:

> Run with --stacktrace option to get the stack trace.

> Run with --info or --debug option to get more log output.

> Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 24s

Exception: Gradle task assembleDebug failed with exit code 1

研究了一下，主因是 JDK 與 Gradle 版本問題，需要多做一些事就能排除了。記錄一下。

此時環境：

% java --version

openjdk 19.0.2 2023-01-17

OpenJDK Runtime Environment (build 19.0.2+7-44)

OpenJDK 64-Bit Server VM (build 19.0.2+7-44, mixed mode, sharing)

這時，在既有專案的左邊上方的 Project 小視窗，挑選 android 目錄，點選右鍵 -> Flutter -> Open Android module in Android Studio -> New Window ，在新的 Android Studio 還沒按 Build 就看到訊息：

Unsupported Java. 

Your build is currently configured to use Java 19.0.2 and Gradle 7.5.

Possible solution:

 - Open Gradle wrapper settings, change `distributionUrl` property to use compatible Gradle version and reload the project

這時就來更換預設的環境： File -> Project Structure -> Project

- Android Gradle Plugin Version: 7.4.2

- Gradle Version: 7.6.1

按下 OK 就會開始抓資料，最後也順利編譯後在模擬器上跑了。