Flutter platform channels实现dart和原生交互

目的

在flutter中调用原生代码，比如调用Android原生的api获取设备的电量

实现

1.首先在MainActivity中增加一个通过原生Api获取设备电量的方法getBatteryLevel()

private fun getBatteryLevel(): Int {
    val batteryLevel: Int
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
      val batteryManager = getSystemService(Context.BATTERY_SERVICE) as BatteryManager
      batteryLevel = batteryManager.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY)
    } else {
      val intent = ContextWrapper(applicationContext).registerReceiver(null, IntentFilter(Intent.ACTION_BATTERY_CHANGED))
      batteryLevel = intent!!.getIntExtra(BatteryManager.EXTRA_LEVEL, -1) * 100 / intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1)
    }
    return batteryLevel
  }

2.然后在MainActivity的onCreate方法中增加如下代码，用于处理从flutter端发送过来的请求消息，若方法名为getBatteryLevel，则调用getBatteryLevel()方法获取电量，通过result对象设置获取的结果

MethodChannel的第二个参数channel name必须唯一

MethodChannel(flutterView, "samples.flutter.dev/battery").setMethodCallHandler { call, result ->
  if (call.method == "getBatteryLevel") {
    val batteryLevel = getBatteryLevel()
    if (batteryLevel != -1) {
      result.success(batteryLevel)
    } else {
      result.error("UNAVAILABLE", "Battery level not available.", null)
    }
  } else {
    result.notImplemented()
  }
}

3.在Flutter端的main.dart的State中创建一个MethodChannel对象，参数须与步骤2中的channel name一致

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

4.在State中新增一个_getBatteryLevel()方法，通过MethodChannel对象调用原生的方法获取设备电量，然后通过setState更新UI显示获取的电量值

String _batteryLevel = '电量';

Future<void> _getBatteryLevel() async {
  String batteryLevel;
  try {
    final int result = await platform.invokeMethod('getBatteryLevel');
    batteryLevel = '电量 $result%';
  } on PlatformException catch (e) {
    batteryLevel = "获取电量失败: '${e.message}'.";
  }

  setState(() {
    _batteryLevel = batteryLevel;
  });
}

完整代码

原生端代码

class MainActivity: FlutterActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    GeneratedPluginRegistrant.registerWith(this)

    MethodChannel(flutterView, "samples.flutter.dev/battery").setMethodCallHandler { call, result ->
      if (call.method == "getBatteryLevel") {
        val batteryLevel = getBatteryLevel()
        if (batteryLevel != -1) {
          result.success(batteryLevel)
        } else {
          result.error("UNAVAILABLE", "Battery level not available.", null)
        }
      } else {
        result.notImplemented()
      }
    }
  }

  private fun getBatteryLevel(): Int {
    val batteryLevel: Int
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
      val batteryManager = getSystemService(Context.BATTERY_SERVICE) as BatteryManager
      batteryLevel = batteryManager.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY)
    } else {
      val intent = ContextWrapper(applicationContext).registerReceiver(null, IntentFilter(Intent.ACTION_BATTERY_CHANGED))
      batteryLevel = intent!!.getIntExtra(BatteryManager.EXTRA_LEVEL, -1) * 100 / intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1)
    }
    return batteryLevel
  }
}

Flutter端代码

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  static const platform = const MethodChannel('samples.flutter.dev/battery');
String _batteryLevel = '电量';

Future<void> _getBatteryLevel() async {
  String batteryLevel;
  try {
    final int result = await platform.invokeMethod('getBatteryLevel');
    batteryLevel = '电量 $result%';
  } on PlatformException catch (e) {
    batteryLevel = "获取电量失败: '${e.message}'.";
  }

  setState(() {
    _batteryLevel = batteryLevel;
  });
}

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Text(
          _batteryLevel,
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _getBatteryLevel,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

Java实现

java实现与kotlin类似，至于iOS的object-c或者swift实现，可以参考官方文档

public class MainActivity extends FlutterActivity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    GeneratedPluginRegistrant.registerWith(this);

    new MethodChannel(getFlutterView(), "samples.flutter.dev/battery").setMethodCallHandler(
            new MethodChannel.MethodCallHandler() {
              @Override
              public void onMethodCall(MethodCall call, MethodChannel.Result result) {
                if (call.method.equals("getBatteryLevel")) {
                  int batteryLevel = getBatteryLevel();

                  if (batteryLevel != -1) {
                    result.success(batteryLevel);
                  } else {
                    result.error("UNAVAILABLE", "Battery level not available.", null);
                  }
                } else {
                  result.notImplemented();
                }
              }
            });
  }

  private int getBatteryLevel() {
    int batteryLevel = -1;
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
      BatteryManager batteryManager = (BatteryManager) getSystemService(BATTERY_SERVICE);
      batteryLevel = batteryManager.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY);
    } else {
      Intent intent = new ContextWrapper(getApplicationContext()).
              registerReceiver(null, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
      batteryLevel = (intent.getIntExtra(BatteryManager.EXTRA_LEVEL, -1) * 100) /
              intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1);
    }
    return batteryLevel;
  }
}

参考

Writing custom platform-specific code