Flutter与原生native互相通信

（本文只列出与Android Native的交互，iOS使用相同的Api，处理方式类似）。主要就是 MethodChannel的使用，因为native端和flutter端都有 methodChannel的setMethodCallHandler()，和invokeMethod()方法，所以两端都可以使用methodChannel进行通信。

Dart调用Native源码：
//Dart端源码

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
...
class _MyHomePageState extends State<MyHomePage> {
  static const platform = const MethodChannel('samples.flutter.dev/battery');

  // Get battery level.
}



// Get battery level.
  String _batteryLevel = 'Unknown battery level.';

  Future<void> _getBatteryLevel() async {
    String batteryLevel;
    try {
      final int result = await platform.invokeMethod('getBatteryLevel');
      batteryLevel = 'Battery level at $result % .';
    } on PlatformException catch (e) {
      batteryLevel = "Failed to get battery level: '${e.message}'.";
    }

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

//Native端，Android Java.(Kotlin类似)。交互代码运行在mainThread主线程。

import io.flutter.app.FlutterActivity;
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;

public class MainActivity extends FlutterActivity {
    private static final String CHANNEL = "samples.flutter.dev/battery";

    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        GeneratedPluginRegistrant.registerWith(this);

        new MethodChannel(getFlutterView(), CHANNEL).setMethodCallHandler(
                new MethodCallHandler() {

                    @Override
                    public void onMethodCall(MethodCall call, Result result) {
                        // Note: this method is invoked on the main thread.
                        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();
                        }
                    }
                });
    }
}

Native发送给flutter数据：（同样使用methodChannel机制）
//native 端。这里是Kotlin,Java类似。

const val CONNECTION_CHANNEL = "com.demo.flutter.connection"

val methodChannel = MethodChannel(flutterView, CONNECTION_CHANNEL)
        methodChannel.setMethodCallHandler { methodCall, result ->
            when (methodCall.method) {
                "activityFinish" -> {
                    goBack() //关闭当前页面
                    result.success(null) //标识调用成功
                }
                "showToastMessage" -> showShortToast(methodCall.argument<String>("message"))
            }
        }


//使用注册的方法channel调用dart端方法名称，并传递参数。
        Handler().postDelayed({
            methodChannel.invokeMethod("aaa", "c")
        }, 5000)；

//dart端

static const _platform = const MethodChannel("com.whitehorse.flutter.connection");

  _AboutPageState() {
    _platform.setMethodCallHandler((handler) {
      switch (handler.method) {
        case "aaa":
          _platform.invokeMethod("showToastMessage", {"message": "您调用了dart里的方法"});
          break;
      }
    });
  }

  void _goBack() {
//    _platform.invokeMethod("activityFinish");
  }

另一种方式，实现native flutter通信：

基于 EventChannel，使用事件流 event stream 驱动，更适合长久耗时的方法调用。

//Native端，android.

public class MainActivity extends FlutterActivity {
    public static final String STREAM = "com.yourcompany.eventchannelsample/stream"; 

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        new EventChannel(getFlutterView(), STREAM).setStreamHandler(
                new EventChannel.StreamHandler() {
                    @Override
                    public void onListen(Object args, final EventChannel.EventSink events) {
                        Log.w(TAG, "adding listener");
                    }

                    @Override
                    public void onCancel(Object args) {
                        Log.w(TAG, "cancelling listener");
                    }
                }
        );
    }
}

//flutter,dart端

static const stream =
    const EventChannel('com.yourcompany.eventchannelsample/stream');

StreamSubscription _timerSubscription = null;

void _enableTimer() {
  if (_timerSubscription == null) {
    _timerSubscription = stream.receiveBroadcastStream().listen(_updateTimer); // 添加监听
  }
}

void _disableTimer() {
  if (_timerSubscription != null) {
    _timerSubscription.cancel();
    _timerSubscription = null;
  }
}

* flutter receiveBroadcastStream([arguments]) 返回一个 broadcast stream对象。使用API进行操作。
https://api.flutter.dev/flutter/dart-async/Stream-class.html。
常用的为 listener。