如何使用EventChannel获取当前时间（Flutter+Kotlin实现）

现存问题 #

• 两端EventChannel名称不匹配：Flutter端定义的通道名为samples.flutter.dev/eventChannel_profile，Kotlin端配置的通道名不一致，会导致通信完全失效
• Kotlin端未保存EventSink实例、未实现时间发送逻辑，且EventSink强制要求在主线程调用，否则Flutter端无法正常接收数据
• Flutter端未实现按钮点击触发逻辑，初始直接监听流会导致进入页面就自动请求时间，不符合点击触发的需求

Kotlin端完整代码 #

直接替换MainActivity中对应代码即可：

import android.util.Log
import android.os.Handler
import android.os.Looper
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.EventChannel

class MainActivity : FlutterActivity() {
    private val EVENT_CHANNEL = "samples.flutter.dev/eventChannel_profile"
    private var eventSink: EventChannel.EventSink? = null
    private val mainHandler = Handler(Looper.getMainLooper())

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        EventChannel(flutterEngine.dartExecutor.binaryMessenger, EVENT_CHANNEL).setStreamHandler(
            object : EventChannel.StreamHandler {
                override fun onListen(arguments: Any?, events: EventChannel.EventSink) {
                    eventSink = events
                    // Flutter端开始监听时，直接发送当前时间戳（毫秒级）
                    sendCurrentTime()
                }

                override fun onCancel(arguments: Any?) {
                    Log.w("Android", "EventChannel onCancel called")
                    eventSink = null
                }
            }
        )
    }

    private fun sendCurrentTime() {
        val time = System.currentTimeMillis()
        // 切换到主线程发送事件，避免线程异常
        mainHandler.post {
            eventSink?.success(time)
        }
    }
}

Flutter端调整后代码 #

补全按钮点击逻辑，改为点击时才触发流监听获取时间：

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);
  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  static const EventChannel _eventPlatform =
      EventChannel('samples.flutter.dev/eventChannel_profile');
  
  int? currentTime;
  StreamSubscription? _timeSub;

  void _getUpdateProfile() {
    _timeSub?.cancel();
    // 点击时开始监听流，触发Kotlin侧onListen回调
    _timeSub = _eventPlatform.receiveBroadcastStream().cast<int>().listen((ts) {
      setState(() {
        currentTime = ts;
      });
      _timeSub?.cancel();
    });
  }

  @override
  void dispose() {
    _timeSub?.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        padding: const EdgeInsets.all(20),
        child: Center(
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              Text(currentTime != null ? "Current Time: $currentTime" : "Waiting for get data..."),
              const SizedBox(height: 30),
              ElevatedButton(
                onPressed: _getUpdateProfile,
                child: const Text('Get Update Profile'),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

注意事项 #

• 时间数据全程仅通过EventChannel传递，无其他通道参与
• 两端通道名必须完全一致，大小写、特殊字符不能有任何偏差
• 页面销毁时必须取消流订阅，避免内存泄漏
• 若需要持续接收时间更新，可移除_timeSub?.cancel()逻辑，Kotlin侧可使用定时器循环调用sendCurrentTime()即可

内容的提问来源于stack exchange，提问作者userName