Flutter框架分析-BasicMessageChannel
1. 前言
在文章Flutter框架分析（八）-Platform Channel中，我们分析了BasicMessageChannel的原理和结构，并详细讲解了与其相关的一些核心类，例如MessageHandler和MessageCodec等，本文主要讲解使用BasicMessageChannel的示例。
2. 使用流程
BasicMessageChannel可用于Flutter给native发消息，也可用于native给Flutter发消息，所以接下来将分别分析这两种使用流程。
2.1 Flutter给native发消息
流程如下：
1）native端创建某channel name的BasicMessageChannel。
2）native端使用setMessageHandler函数，设置该BasicMessageChannel的MessageHandler。
3）Flutter端创建该channel name的BasicMessageChannel。
4）Flutter端使用该BasicMessageChannel通过send函数向native端发送消息。
5）native端刚刚注册的MessageHandler收到发送的消息，在onMessage中处理消息，通过reply函数进行回复。
6）Flutter端处理该回复。
Flutter端关键代码如下：
class _MessageChannelState extends State<MessageChannelWidget> {
static const _channel = BasicMessageChannel('flutter2/testmessagechannel', JSONMessageCodec());
int i = 0;
void _sendMessage() async {
final String reply = await _channel.send('Hello World i: $i');
print('MessageChannelTest in dart $reply');
setState(() {
i++;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("message channel test"),
),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$i',
style: Theme.*of*(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed:_sendMessage,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods);
}
}
native端关键代码如下：
class MessageChannelActivity: FlutterActivity() {
companion object {
fun startActivity(activity: Activity) {
val intent = Intent(activity, MessageChannelActivity::class.java)
activity.startActivity(intent)
}
}
override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
Log.d("MessageChannelTest", "MessageChannelActivity configureFlutterEngine")
val channel = BasicMessageChannel(
flutterEngine.dartExecutor.binaryMessenger,
"flutter2/testmessagechannel",
JSONMessageCodec.INSTANCE)
// Receive messages from Dart
channel.setMessageHandler {message, reply ->
Log.d("MessageChannelTest", "in android Received message = $message")
reply.reply("Reply from Android")
}
}
}
2.2 native给Flutter发消息
流程如下：
1） Flutter端创建该channel name的BasicMessageChannel。
2） Flutter端使用setMessageHandler函数，设置该BasicMessageChannel的Handler函数。
3） native端创建某channel name的BasicMessageChannel。
4） native端使用该BasicMessageChannel通过send函数向Flutter端发送消息。
5） Flutter端刚刚注册的Handler收到发送的消息，并处理消息，然后通过reply函数进行回复。
6） native端处理该回复。
Flutter端关键代码如下：
class _MessageChannelState extends State<MessageChannelWidget> {
static const _channel = BasicMessageChannel('flutter2/testmessagechannel', JSONMessageCodec());
int i = 0;
void _sendMessage() async {
final String reply = await _channel.send('Hello World i: $i');
print('MessageChannelTest in dart $reply');
setState(() {
i++;
});
}
@override
void initState() {
// Receive messages from platform
_channel.setMessageHandler((dynamic message) async {
print('MessageChannelTest in dart Received message = $message');
return 'Reply from Dart';
});
super.initState();
}
}
native端关键代码如下：
class MessageChannelActivity: FlutterActivity() {
companion object {
fun startActivity(activity: Activity) {
val intent = Intent(activity, MessageChannelActivity::class.java)
activity.startActivity(intent)
}
}
override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
Log.d("MessageChannelTest", "MessageChannelActivity configureFlutterEngine")
val channel = BasicMessageChannel(
flutterEngine.dartExecutor.binaryMessenger,
"flutter2/testmessagechannel",
JSONMessageCodec.INSTANCE)
// Send message to Dart
Handler().postDelayed( {
channel.send("Hello World from Android") { reply ->
Log.d("MessageChannelTest", "in android $reply")
}
}, 500)
}
}
3. 小结
本文主要介绍了BasicMessageChannel的使用流程，并列举了一个使用BasicMessageChannel的示例。
