Flutter和原生交互学习

PlatformChannel功能简介

PlatformChannel分为BasicMessageChannel、MethodChannel以及EventChannel三种。其各自的主要用途如下：

• BasicMessageChannel: 用于传递数据。Flutter与原生项目的资源是不共享的，可以通过BasicMessageChannel来获取Native项目的图标等资源。
• MethodChannel: 传递方法调用。Flutter主动调用Native的方法，并获取相应的返回值。比如获取系统电量，发起Toast等调用系统API，可以通过这个来完成。
• EventChannel: 传递事件。这里是Native将事件通知到Flutter。比如Flutter需要监听网络情况，这时候MethodChannel就无法胜任这个需求了。EventChannel可以将Flutter的一个监听交给Native，Native去做网络广播的监听，当收到广播后借助EventChannel调用Flutter注册的监听，完成对Flutter的事件通知。

其实可以看到，无论传方法还是传事件，其本质上都是数据的传递，不过上层包的一些逻辑不同而已。

flutter

import 'dart:async';

import 'package:flutter/material.dart';

import 'package:flutter/services.dart';

class ChannelPage extends StatefulWidget {

  @override

  State<StatefulWidget> createState() {

    return new _ChannelPageState();

  }

}

class _ChannelPageState extends State<ChannelPage> {

  //获取到插件与原生的交互通道

  static const jumpPlugin = const MethodChannel('com.example.jump/plugin');

  static const counterPlugin = const EventChannel('com.example.counter/plugin');

  var _count;

  StreamSubscription _counterSub;

  @override

  void initState() {

    super.initState();

    _startCounterPlugin();

  }

  @override

  void dispose() {

    super.dispose();

    _endCounterPlugin();

  }

  void _startCounterPlugin(){

    if(_counterSub == null){

      _counterSub =  counterPlugin.receiveBroadcastStream().listen(_onCounterEvent,onError: _onCounterError);

    }

  }

  void _endCounterPlugin(){

    if(_counterSub != null){

      _counterSub.cancel();

    }

  }

  void _onCounterError(Object error) {

    setState(() {

      _count = "计时器异常";

      print(error);

    });

  }

  void _onCounterEvent(Object event) {

    setState(() {

      _count = event;

    });

  }

  Future<Null> _jumpToNative() async {

    String result = await jumpPlugin.invokeMethod('oneAct');

    print(result);

  }

  Future<Null> _jumpToNativeWithValue() async {

    Map<String, String> map = { "flutter": "这是一条来自flutter的参数" };

    String result = await jumpPlugin.invokeMethod('twoAct', map);

    print(result);

  }

  @override

  Widget build(BuildContext context) {

    return new Scaffold(

      appBar: new AppBar(

        title: new Text("Channel"),

        centerTitle: true,

      ),

      body: new Center(

          child: new ListView(

            children: <Widget>[

              new Padding(

                padding: const EdgeInsets.only(left: 10.0, top: 10.0, right: 10.0),

                child: new RaisedButton(

                    textColor: Colors.black,

                    child: new Text('跳转到原生界面'),

                    onPressed: () {

                      _jumpToNative();

                    }),

              ),

              new Padding(

                padding: const EdgeInsets.only(

                    left: 10.0, top: 10.0, right: 10.0),

                child: new RaisedButton(

                    textColor: Colors.black,

                    child: new Text('跳转到原生界面(带参数)'),

                    onPressed: () {

                      _jumpToNativeWithValue();

                    }),

              ),

              new Padding(

                padding: const EdgeInsets.only(

                    left: 10.0, top: 10.0, right: 10.0),

                child: new Text('这是一个从原生发射过来的数据：$_count'),

              ),

            ],

          )

      ),

    );

  }

}

android

package com.example.flutter_app.plugins;

import android.app.Activity;

import android.util.Log;

import io.flutter.plugin.common.EventChannel;

import io.flutter.plugin.common.PluginRegistry;

public class FlutterPluginCounter implements EventChannel.StreamHandler {

    public static String CHANNEL = "com.example.counter/plugin";

    static EventChannel channel;

    private Activity activity;

    private FlutterPluginCounter(Activity activity) {

        this.activity = activity;

    }

    public static void registerWith(PluginRegistry.Registrar registrar) {

        channel = new EventChannel(registrar.messenger(), CHANNEL);

        FlutterPluginCounter instance = new FlutterPluginCounter(registrar.activity());

        channel.setStreamHandler(instance);

       // basicMessageChannel = new BasicMessageChannel<String> ("foo", StringCodec.INSTANCE);

    }

    @Override

    public void onListen(Object o, final EventChannel.EventSink eventSink) {

        eventSink.success(123456);

    }

    @Override

    public void onCancel(Object o) {

        Log.i("FlutterPluginCounter", "FlutterPluginCounter:onCancel");

    }

}

package com.example.flutter_app.plugins;

import android.app.Activity;

import android.content.Intent;

import com.example.flutter_app.OneActivity;

import com.example.flutter_app.TwoActivity;

import io.flutter.plugin.common.MethodCall;

import io.flutter.plugin.common.MethodChannel;

import io.flutter.plugin.common.MethodChannel.MethodCallHandler;

import io.flutter.plugin.common.PluginRegistry;

public class FlutterPluginJumpToAct implements MethodCallHandler {

    public static String CHANNEL = "com.example.jump/plugin";

    static MethodChannel channel;

    private Activity activity;

    private FlutterPluginJumpToAct(Activity activity) {

        this.activity = activity;

    }

    public static void registerWith(PluginRegistry.Registrar registrar) {

        channel = new MethodChannel(registrar.messenger(), CHANNEL);

        FlutterPluginJumpToAct instance = new FlutterPluginJumpToAct(registrar.activity());

        //setMethodCallHandler在此通道上接收方法调用的回调

        channel.setMethodCallHandler(instance);

    }

    @Override

    public void onMethodCall(MethodCall call, MethodChannel.Result result) {

        //通过MethodCall可以获取参数和方法名，然后再寻找对应的平台业务，本案例做了2个跳转的业务

        //接收来自flutter的指令oneAct

        if (call.method.equals("oneAct")) {

            //跳转到指定Activity

            Intent intent = new Intent(activity, OneActivity.class);

            activity.startActivity(intent);

            //返回给flutter的参数

            result.success("success");

        }

        //接收来自flutter的指令twoAct

        else if (call.method.equals("twoAct")) {

            //解析参数

            String text = call.argument("flutter");

            //带参数跳转到指定Activity

            Intent intent = new Intent(activity, TwoActivity.class);

            intent.putExtra(TwoActivity.VALUE, text);

            activity.startActivity(intent);

            //返回给flutter的参数

            result.success("success");

        }

        else {

            result.notImplemented();

        }

    }

}

package com.example.flutter_app;

import android.app.Activity;

import android.content.Intent;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

public class OneActivity extends Activity implements View.OnClickListener {

    private Button mGoFlutterBtn;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_one);

        mGoFlutterBtn = findViewById(R.id.go_flutter);

        mGoFlutterBtn.setOnClickListener(this);

    }

    @Override

    public void onClick(View view) {

        switch (view.getId()) {

            case R.id.go_flutter:

                Intent intent = new Intent(this, MainActivity.class);

                startActivity(intent);

                break;

        }

    }

}

package com.example.flutter_app;

import android.app.Activity;

import android.os.Bundle;

import android.widget.TextView;

public class TwoActivity extends Activity{

    private TextView mTextView;

    public static final String VALUE = "value";

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_two);

        mTextView = findViewById(R.id.text);

        String text = getIntent().getStringExtra(VALUE);

        mTextView.setText(text);

    }

}

package com.example.flutter_app;

import android.os.Bundle;

import com.example.flutter_app.plugins.FlutterPluginCounter;

import com.example.flutter_app.plugins.FlutterPluginJumpToAct;

import io.flutter.app.FlutterActivity;

import io.flutter.plugins.GeneratedPluginRegistrant;

public class MainActivity extends FlutterActivity {

  @Override

  protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    GeneratedPluginRegistrant.registerWith(this);

    FlutterPluginJumpToAct.registerWith(this.registrarFor(FlutterPluginJumpToAct.CHANNEL));//注册

    FlutterPluginCounter.registerWith(this.registrarFor(FlutterPluginCounter.CHANNEL));//注册

  }

}

效果：