Kotlin开发Android应用连接HiveMQ时whenComplete未执行求助

问题描述 #

用Kotlin开发Android应用，通过HiveMQ发布消息给ESP8266，参考官方文档适配代码后，调试日志始终不打印，推测whenComplete回调从未执行。代码如下：

val builder = MqttClient.builder()
    .identifier(UUID.randomUUID().toString())
    .serverHost("server.hivemq.cloud")
    .serverPort(8883)
    .sslWithDefaultConfig();

val client = builder.useMqttVersion5().buildAsync();

client.connectWith()
    .simpleAuth()
    .username("username")
    .password("password".toByteArray())
    .applySimpleAuth()
    .send()
    .whenComplete { connAck, throwable ->
        run {
            Log.d("TAG", "Some debug string");
            if (throwable != null) {
                Toast.makeText(
                    context,
                    "Unable to connect to HiveMQ servers!!",
                    Toast.LENGTH_LONG
                ).show();
            } else {
                client.publishWith()
                    .topic("my/topic")
                    .payload("ChopChop".toByteArray())
                    .send()
                    .whenComplete { publish, throwable ->
                        run {
                            if(throwable != null) {
                                Toast.makeText(context, "Unable to publish message!", Toast.LENGTH_LONG).show();
                            }
                            client.disconnect();
                        }
                    }
            }
        }
    }

排查线索 #

• 检查网络权限：确保AndroidManifest.xml中添加互联网权限：

  <uses-permission android:name="android.permission.INTERNET" />
  

  Android 9及以上默认禁止明文流量，但HiveMQ Cloud用8883端口（SSL加密），无需额外配置usesCleartextTraffic，但权限必须存在。

• 线程问题：whenComplete回调默认在后台线程执行，直接调用Toast.makeText会触发主线程异常，导致回调执行中断且无日志。需将UI操作切换到主线程，比如用Handler(Looper.getMainLooper()).post{ ... }包裹Toast代码。

• 添加异常捕获：在send()后追加exceptionally方法，捕获请求发送阶段的异常（比如网络连接失败、参数错误），避免异常被直接吞掉：

  .send()
  .exceptionally { throwable ->
      Log.e("TAG", "Request failed", throwable)
      null
  }
  

• 检查Logcat配置：确认Logcat的TAG过滤正确，没有隐藏Debug级别日志，且选择了当前应用进程。

• SSL证书验证：设备时间不正确会导致SSL证书验证失败，检查设备系统时间是否同步。若仍有问题，可尝试自定义SSL配置（比如信任HiveMQ的证书）。

• 客户端生命周期：client是局部变量，可能在回调执行前被GC回收，将其改为类成员变量，延长生命周期。

修正后的代码示例 #

import android.os.Handler
import android.os.Looper
import android.widget.Toast
import org.eclipse.paho.mqttv5.client.MqttClient
import java.util.UUID

// 将client设为类成员变量，避免被提前回收
private lateinit var client: MqttClient

fun connectAndPublish(context: Context) {
    val builder = MqttClient.builder()
        .identifier(UUID.randomUUID().toString())
        .serverHost("server.hivemq.cloud")
        .serverPort(8883)
        .sslWithDefaultConfig()

    client = builder.useMqttVersion5().buildAsync()

    client.connectWith()
        .simpleAuth()
        .username("username")
        .password("password".toByteArray())
        .applySimpleAuth()
        .send()
        .exceptionally { throwable ->
            Log.e("TAG", "Connect request failed", throwable)
            Handler(Looper.getMainLooper()).post {
                Toast.makeText(context, "Connect request failed!", Toast.LENGTH_LONG).show()
            }
            null
        }
        .whenComplete { connAck, throwable ->
            Log.d("TAG", "Connect callback triggered")
            Handler(Looper.getMainLooper()).post {
                if (throwable != null) {
                    Log.e("TAG", "Connect failed", throwable)
                    Toast.makeText(
                        context,
                        "Unable to connect to HiveMQ servers!!",
                        Toast.LENGTH_LONG
                    ).show()
                } else {
                    Log.d("TAG", "Connected successfully")
                    client.publishWith()
                        .topic("my/topic")
                        .payload("ChopChop".toByteArray())
                        .send()
                        .exceptionally { publishThrowable ->
                            Log.e("TAG", "Publish request failed", publishThrowable)
                            Handler(Looper.getMainLooper()).post {
                                Toast.makeText(context, "Publish request failed!", Toast.LENGTH_LONG).show()
                            }
                            null
                        }
                        .whenComplete { publish, publishThrowable ->
                            Handler(Looper.getMainLooper()).post {
                                if (publishThrowable != null) {
                                    Log.e("TAG", "Publish failed", publishThrowable)
                                    Toast.makeText(context, "Unable to publish message!", Toast.LENGTH_LONG).show()
                                }
                                client.disconnect()
                            }
                        }
                }
            }
        }
}

内容的提问来源于stack exchange，提问作者Gaurav Joseph