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
老孟Flutter博客（330个控件用法+实战入门系列文章）：http://laomengit.com
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