最近flutter不是一般的火呀，但对于一些成熟的产品来说，完全摒弃原有App的历史沉淀，全面转向Flutter是不现实的。因此使用Flutter去统一Android、iOS技术栈，把它作为已有原生App的扩展能力，通过有序推进来提升移动端的开发效率
（1）创建flutter模块，创建module后会AS会自动进行flutter的相关配置

（2）将FlutterActivity添加到AndroidManifest.xml

        <activity
            android:name="io.flutter.embedding.android.FlutterActivity"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:theme="@style/FlutterTheme"
            android:windowSoftInputMode="adjustResize" />

（3）跳转到flutter页面

startActivity(FlutterActivity.withNewEngine().initialRoute("route").build(this))

（4）你也可以使用缓存的FlutterEngine，可以减少加载延迟
在MyApplication中实例化一个FlutterEngine

class MyApplication : Application() { 
    lateinit var flutterEngine: FlutterEngine
    override fun onCreate() { 
        super.onCreate()
        flutterEngine = FlutterEngine(this)
        flutterEngine.dartExecutor.executeDartEntrypoint(DartExecutor.DartEntrypoint.createDefault())
        FlutterEngineCache.getInstance().put("my_engine_id", flutterEngine)
    }
}

然后在Activity中跳转

        btn.setOnClickListener { 
            startActivity(FlutterActivity.withCachedEngine("my_engine_id").build(this))
        }

注意：使用withCachedEngine()工厂方法时，请传递与缓存所需的ID相同的ID FlutterEngine

设置缓存引擎时也可以初始路由，修改MyApplication

        flutterEngine = FlutterEngine(this)
        flutterEngine.navigationChannel.setInitialRoute("route") //可以借此携带一些字符串数据，可传递到flutter页面
        flutterEngine.dartExecutor.executeDartEntrypoint(DartExecutor.DartEntrypoint.createDefault())
        FlutterEngineCache.getInstance().put("my_engine_id", flutterEngine)

对应的dart

import 'dart:ui';
import 'package:flutter/material.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: _widgetForRoute(window.defaultRouteName),
    );
  }
}

//路由的选择
Widget _widgetForRoute(String route) { 
  switch (route) { 
    case 'route':
      return MaterialApp(
        home: Scaffold(
          appBar: AppBar(
            title: Text('Flutter页面'),
          ),
          body: Center(
            child: Text('行走的猪蹄',
                style: TextStyle(color: Colors.red),
                textDirection: TextDirection.ltr),
          ),
        ),
      );
    default:
      return Center(
        child: Text('Unknown route: $route',
            style: TextStyle(color: Colors.red),
            textDirection: TextDirection.ltr),
      );
  }
}