【Flutter 混合开发】与原生通信-MethodChannel

Flutter 混合开发系列包含如下：

嵌入原生View-Android

嵌入原生View-iOS

与原生通信-MethodChannel

与原生通信-BasicMessageChannel

与原生通信-EventChannel

添加 Flutter 到 Android Activity

添加 Flutter 到 Android Fragment

添加 Flutter 到 iOS

每个工作日分享一篇，欢迎关注、点赞及转发。

平台通信的3中方式

Flutter 与 Native 端通信有如下3个方法：

MethodChannel：Flutter 与 Native 端相互调用，调用后可以返回结果，可以 Native 端主动调用，也可以Flutter主动调用，属于双向通信。此方式为最常用的方式， Native 端调用需要在主线程中执行。
BasicMessageChannel：用于使用指定的编解码器对消息进行编码和解码，属于双向通信，可以 Native 端主动调用，也可以Flutter主动调用。
EventChannel：用于数据流（event streams）的通信， Native 端主动发送数据给 Flutter，通常用于状态的监听，比如网络变化、传感器数据等。

通信架构图

此图为官方的架构图

Flutter 与 Native 端通信是异步的。

通信与平台线程

Native 端主动发送数据给 Flutter时，Native 端代码需要在主线程中执行，Android 端从子线程跳转到主线程方式：

Kotlin 代码：

Handler(Looper.getMainLooper()).post {

}

Java 代码：

new Handler(Looper.getMainLooper()).post(new Runnable() {

  @Override

  public void run() {

  }

});

如果可以获取到当前 Activity，也可以使用如下方式：

activity.runOnUiThread {

}

iOS 端从子线程跳转到主线程方式：

Objective-C 代码：

dispatch_async(dispatch_get_main_queue(), ^{

});

Swift 代码：

DispatchQueue.main.async {

}

MethodChannel

Flutter 端

Flutter 端创建 MethodChannel 通道，用于与原生端通信：

var channel = MethodChannel('com.flutter.guide.MethodChannel');

com.flutter.guide.MethodChannel 是 MethodChannel 的名称，原生端要与之对应。

发送消息：

var result = await channel.invokeMethod('sendData',{'name': 'laomeng', 'age': 18})

第一个参数表示method，方法名称，原生端会解析此参数。
第二个参数表示参数，类型任意，多个参数通常使用Map。
返回 Future，原生端返回的数据。

完整代码：

class MethodChannelDemo extends StatefulWidget {

  @override

  _MethodChannelDemoState createState() => _MethodChannelDemoState();

}

class _MethodChannelDemoState extends State<MethodChannelDemo> {

  var channel = MethodChannel('com.flutter.guide.MethodChannel');

  var _data;

  @override

  Widget build(BuildContext context) {

    return Scaffold(

      appBar: AppBar(),

      body: Column(

        children: [

          SizedBox(

            height: 50,

          ),

          RaisedButton(

            child: Text('发送数据到原生'),

            onPressed: () async {

              var result = await channel

                  .invokeMethod('sendData', {'name': 'laomeng', 'age': 18});

              var name = result['name'];

              var age = result['age'];

              setState(() {

                _data = '$name,$age';

              });

            },

          ),

          Text('原生返回数据：$_data')

        ],

      ),

    );

  }

}

Android 端

android 下创建 MethodChannelDemo：

package com.flutter.guide

import io.flutter.plugin.common.BinaryMessenger

import io.flutter.plugin.common.MethodCall

import io.flutter.plugin.common.MethodChannel

/**

 * des:

 */

class MethodChannelDemo(messenger: BinaryMessenger): MethodChannel.MethodCallHandler {

    private var channel: MethodChannel

    init {

        channel = MethodChannel(messenger, "com.flutter.guide.MethodChannel")

        channel.setMethodCallHandler(this)

    }

    override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {

    }

}

onMethodCall 方法在 Flutter 端调用 invokeMethod 方法回调，解析方法如下：

override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {

    if (call.method == "sendData") {

        val name = call.argument("name") as String?

        val age = call.argument("age") as Int?

        var map = mapOf("name" to "hello,$name",

                "age" to "$age"

        )

        result.success(map)

    }

}

call.method 字符串就是 invokeMethod 方法传入的 method。
call.argument 是 invokeMethod 传入的参数，由于 Flutter 端传入的是 Map，所以上面的解析按照 Map 解析。
result.success() 是返回给 Flutter 的结果。

Flutter 端解析：

var result = await channel

    .invokeMethod('sendData', {'name': 'laomeng', 'age': 18});

var name = result['name'];

var age = result['age'];

两端的解析要相互对应。

在 MainActivity 启动：

class MainActivity : FlutterActivity() {

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {

        super.configureFlutterEngine(flutterEngine)

        MethodChannelDemo(flutterEngine.dartExecutor.binaryMessenger)

    }

}

iOS 端

ios 下创建 MethodChannelDemo，按如下方式：

import Flutter

import UIKit

public class MethodChannelDemo {

    init(messenger: FlutterBinaryMessenger) {

        let channel = FlutterMethodChannel(name: "com.flutter.guide.MethodChannel", binaryMessenger: messenger)

        channel.setMethodCallHandler { (call:FlutterMethodCall, result:@escaping FlutterResult) in

            if (call.method == "sendData") {

                if let dict = call.arguments as? Dictionary<String, Any> {

                    let name:String = dict["name"] as? String ?? ""

                    let age:Int = dict["age"] as? Int ?? -1

                    result(["name":"hello,\(name)","age":age])

                }

            }

        }

    }

}

在 AppDelegate 启动：

import UIKit

import Flutter

@UIApplicationMain

@objc class AppDelegate: FlutterAppDelegate {

  override func application(

    _ application: UIApplication,

    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?

  ) -> Bool {

    let controller : FlutterViewController = window?.rootViewController as! FlutterViewController

    MethodChannelDemo(messenger: controller.binaryMessenger)

    GeneratedPluginRegistrant.register(with: self)

    return super.application(application, didFinishLaunchingWithOptions: launchOptions)

  }

}

原生端主动发送消息给Flutter

Flutter 端接收数据

@override

void initState() {

  super.initState();

  channel.setMethodCallHandler((call) {

    setState(() {

      _nativeData = call.arguments['count'];

    });

  });

}

Android 发送数据

原生端启动定时器，每隔一秒向 Flutter 发送数据，Android 端代码：

class MethodChannelDemo(var activity: Activity, messenger: BinaryMessenger) : MethodChannel.MethodCallHandler {

    private var channel: MethodChannel

    private var count = 0

    init {

        channel = MethodChannel(messenger, "com.flutter.guide.MethodChannel")

        channel.setMethodCallHandler(this)

        startTimer()

    }

    fun startTimer() {

        var timer = Timer().schedule(timerTask {

            activity.runOnUiThread {

                var map = mapOf("count" to count++)

                channel.invokeMethod("timer", map)

            }

        }, 0, 1000)

    }

    override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {

        if (call.method == "sendData") {

            val name = call.argument("name") as String?

            val age = call.argument("age") as Int?

            var map = mapOf("name" to "hello,$name",

                    "age" to "$age"

            )

            result.success(map)

        }

    }

}

注意：Android 端发送数据要在主现场中调用，即：

activity.runOnUiThread {

             var map = mapOf("count" to count++)

             channel.invokeMethod("timer", map)

         }

启动修改如下：

class MainActivity : FlutterActivity() {

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {

        super.configureFlutterEngine(flutterEngine)

        MethodChannelDemo(this,flutterEngine.dartExecutor.binaryMessenger)

        flutterEngine.plugins.add(MyPlugin())

    }

}

iOS 发送数据

iOS 端启动定时器代码如下：

import Flutter

import UIKit

public class MethodChannelDemo {

    var count =  0

    var channel:FlutterMethodChannel

    init(messenger: FlutterBinaryMessenger) {

        channel = FlutterMethodChannel(name: "com.flutter.guide.MethodChannel", binaryMessenger: messenger)

        channel.setMethodCallHandler { (call:FlutterMethodCall, result:@escaping FlutterResult) in

            if (call.method == "sendData") {

                if let dict = call.arguments as? Dictionary<String, Any> {

                    let name:String = dict["name"] as? String ?? ""

                    let age:Int = dict["age"] as? Int ?? -1

                    result(["name":"hello,\(name)","age":age])

                }

            }

        }

        startTimer()

    }

    func startTimer() {

        var timer = Timer.scheduledTimer(timeInterval:1, target: self, selector:#selector(self.tickDown),userInfo:nil,repeats: true)

    }

    @objc func tickDown(){

        count += 1

        var args = ["count":count]

        channel.invokeMethod("timer", arguments:args)

    }

}

交流

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