场景

1. Flutter项目中需要与Native进行通信
2. Android原生项目嵌入Flutter开发模块
3. iOS原生项目嵌入Flutter开发模块
4. Flutter插件开发

image

平台通道数据类型支持

当在发送和接收值时，这些值在消息中的序列化和反序列化会自动进行。

平台通道

Platform Channel 是所以 Flutter 提供的和平台端通信的工具，针对不同的使用场景，Platform Channel 又分为以下三类：

1. Message channel：用于传递字符串和半结构化的信息,支持使用自定义消息编解码器进行基本的异步消息传递
2. Method channel：用于传递方法调用（method invocation）
3. Event channel：用于数据流（event streams）的通信,通常用在需要进行实时监听的使用场景，比如：网络状态，电池充电状态以及一些监听器的实现

Flutter项目中需要与Native进行通信-实战

我们这里仅使用Method channel和Event channel进行通信实战

要实现的功能：

1. Flutter给Native传递三个参数，Native要把这三个参数相加得到的结果返回给Flutter，并显示在Flutter界面上
2. Native写一个定时器，每隔1秒进行“+1操作”，每次“+1”后，把结果传递给Flutter，当结果大于30的时候结束定时器

功能1：

Android端：

创建MethodChannelDemo.kt

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

    private var channel: MethodChannel = MethodChannel(messenger, "com.mufeng.flutterNativeChannel.MethodChannel")

    init {
        channel.setMethodCallHandler(this)
    }

    override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {
        when(call.method){
            "add" -> {
                val params1 = call.argument<Int>("params1")
                val params2 = call.argument<Int>("params2")
                val params3 = call.argument<Int>("params3")
                val params = params1!! + params2!! + params3!!
                result.success(params)
            }
        }
    }
}

在MainActivity中启动平台通道

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

iOS端

创建MethodChannelDemo.swift

//
//  MethodChannelDemo.swift
//  Runner
//
//  Created by a on 2020/12/28.
//

import Foundation

import Flutter
import UIKit

public class MethodChannelDemo {
    init(messenger: FlutterBinaryMessenger) {
        let channel = FlutterMethodChannel(name: "com.mufeng.flutterNativeChannel.MethodChannel", binaryMessenger: messenger)
        channel.setMethodCallHandler{ (call: FlutterMethodCall, result:@escaping FlutterResult)in
            if(call.method == "add"){
                if let dict = call.arguments as? Dictionary<String, Any>{
                    let params1: Int = dict["params1"] as? Int ?? 0
                    let params2: Int = dict["params2"] as? Int ?? 0
                    let params3: Int = dict["params3"] as? Int ?? 0
                    result(params1 + params2 + params3)
                }
            }
        }
    }
}

在 AppDelegate 中启动平台通道：

import UIKit
import Flutter

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    
    /// start
    let controller: FlutterViewController = window?.rootViewController as! FlutterViewController
    MethodChannelDemo(messenger: controller.binaryMessenger)
    /// end
    GeneratedPluginRegistrant.register(with: self)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

在ios中也用同样的操作，要保证平台通道的channel保持一致，这样在Flutter中就可以保证一套代码试用两个平台了

Flutter

 /// 保证平台channel保持一致
 var channel = MethodChannel('com.mufeng.flutterNativeChannel.MethodChannel');
 var result = await channel.invokeMethod('add', {'params1': int.parse(controller1.text), 'params2': int.parse(controller2.text), 'params3': int.parse(controller3.text)});
 setState(() {
   this.result = result.toString();
 });

显示结果：

Android：

image

iOS:

image

功能2：

Android端

android 下创建 EventChannelDemo：

package com.mufeng.flutter_native_channel

import android.app.Activity
import io.flutter.plugin.common.BinaryMessenger
import io.flutter.plugin.common.EventChannel
import java.util.*
import kotlin.concurrent.timerTask

class EventChannelDemo(private var activity: Activity, messenger: BinaryMessenger) : EventChannel.StreamHandler {

    private var channel: EventChannel = EventChannel(messenger, "com.mufeng.flutterNativeChannel.EventChannel")
    private var count = 0
    private var events: EventChannel.EventSink? = null
    init {
        channel.setStreamHandler(this)
        startTimer()
    }

    private fun startTimer() {
        var timer = Timer().schedule(timerTask {
            count++
            val map = mapOf("count" to count)
            activity.runOnUiThread {
                // 必须运行在主线程
                events?.success(map)
            }
            if(count >= 30){
                 activity.runOnUiThread {
                    events?.error("400", "超过30秒,倒计时结束", null)
                }
                cancel()
            }
        }, 0, 1000)
    }

    override fun onListen(arguments: Any?, events: EventChannel.EventSink?) {
        this.events = events
    }

    override fun onCancel(arguments: Any?) {
        this.events = null
    }
}

在 MainActivity 启动：

class MainActivity: FlutterActivity() {
    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        // MethodChannelDemo(flutterEngine.dartExecutor.binaryMessenger)
        EventChannelDemo(this, flutterEngine.dartExecutor.binaryMessenger)
    }
}

iOS端

ios 下创建 EventChannelDemo

import Foundation
import Flutter
import UIKit

public class EventChannelDemo: NSObject, FlutterStreamHandler {
    var channel: FlutterEventChannel?
    var count = 0
    var events: FlutterEventSink?
    var timer: Timer?
    
    public override init() {
        super.init()
    }
    
    convenience init(messenger: FlutterBinaryMessenger) {
        self.init()
        
        channel = FlutterEventChannel(name: "com.mufeng.flutterNativeChannel.EventChannel", binaryMessenger: messenger)
        channel?.setStreamHandler(self)
        startTimer()
    }
    
    func startTimer() {
        timer = Timer.scheduledTimer(timeInterval: 1, target: self,selector: #selector(self.tickDown),userInfo: nil,repeats: true)
    }
    
    @objc func tickDown(){
        count += 1
        let args = ["count": count]
        if(events != nil){
            events!(args)
        }
        if(count >= 30){
            if(events != nil){
                events!(FlutterError.init(code: "400", message: "超过30秒,倒计时结束", details: nil))
            }
            timer?.fireDate = Date.distantFuture
            timer?.invalidate()
        }
    }
    
    public func onListen(withArguments arguments: Any?, eventSink events: @escaping FlutterEventSink) -> FlutterError? {
        self.events = events
        return nil
    }
    
    public func onCancel(withArguments arguments: Any?) -> FlutterError? {
        self.events = nil
        timer?.invalidate()
        self.timer = nil
        return nil
    }
}

在 AppDelegate 启动：

@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)
    EventChannelDemo(messenger: controller.binaryMessenger)
    GeneratedPluginRegistrant.register(with: self)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

Flutter端

var _eventChannel = EventChannel('com.mufeng.flutterNativeChannel.EventChannel');

_eventChannel.receiveBroadcastStream().listen(_listen, onError: (value){
      print(value);
    });
    
  void _listen(event) {
    setState(() {
      second = event['count'].toString();
    });
  }

显示结果

Android：

// 打印出原生发挥的错误信息
I/flutter (24053): PlatformException(400, 超过30秒,倒计时结束, null, null)

image

iOS：

// 打印出原生发挥的错误信息
flutter: PlatformException(400, 超过30秒,倒计时结束, null, null)

image

源码地址：flutter_native_channel

总结

Flutter 与 Native 通信在 Flutter 应用中几乎是不可缺少的步骤，所以掌握其原理和实际用法尤其重要。熟练的掌握Flutter与Native的通信能极大的提高开发效率

感谢

老孟Flutter

Flutter中文网-Flutter实战