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# 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 {
  
}
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Java 代码:

new Handler(Looper.getMainLooper()).post(new Runnable() {
  @Override
  public void run() {
    
  }
});
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如果可以获取到当前 Activity,也可以使用如下方式:

activity.runOnUiThread {
   
}
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iOS 端从子线程跳转到主线程方式:

Objective-C 代码:

dispatch_async(dispatch_get_main_queue(), ^{
  
});
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Swift 代码:

DispatchQueue.main.async {
  
}
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# 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');
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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})
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  • 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 {
  
  _MethodChannelDemoState createState() => _MethodChannelDemoState();
}

class _MethodChannelDemoState extends State<MethodChannelDemo> {
  var channel = MethodChannel('com.flutter.guide.MethodChannel');

  var _data;

  
  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')
        ],
      ),
    );
  }
}
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# 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) {
        
    }
}
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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)
    }
}
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  • 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'];
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两端的解析要相互对应。

MainActivity 启动:

class MainActivity : FlutterActivity() {
    
    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        MethodChannelDemo(flutterEngine.dartExecutor.binaryMessenger)
    }
}
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# 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])
                }
            }
        }
    }
}

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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)
  }
}

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# 原生端主动发送消息给Flutter

# Flutter 端接收数据

void initState() {
  super.initState();
  channel.setMethodCallHandler((call) {
    setState(() {
      _nativeData = call.arguments['count'];
    });
  });
}
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# 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)
        }
    }
}
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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)
            }
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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())
    }
}
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# 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: 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)
    }
     func tickDown(){
        count += 1
        var args = ["count":count]
        channel.invokeMethod("timer", arguments:args)
    }
}

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