在 Unity 中使用 MQTTnet

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前言

2025年3月24日

Unity 2022.3.54f1

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MQTT X

桌面客户端，用于查看和测试 MQTT
官网地址：https://mqttx.app/

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免费的公共 MQTT 服务器

官网地址：https://www.emqx.com/zh/mqtt/public-mqtt5-broker

Broker：broker.emqx.io
TCP 端口：1883
主题：testtopic/#（注意默认禁止了 $SYS 主题和 # 主题，此处可换为其他的，还挺多的 test 之类的）
MQTT版本：5.0

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MQTTnet.dll

两种方式导入 MQTTnet ，
1、从 nuget.org 把包下载下来，解压后将对应平台的 dll 从 lib 文件夹中取出来，放到 Plugins 文件夹。
2、为 Unity 安装 NuGetForUnity 包管理器，通过它搜索 MQTTnet 安装。

注意 dll 的版本的依赖，是否为 Unity 所支持

Unity3D 入门：为 Unity 的 C# 项目添加 dll 引用或安装 NuGet 包
Unity3D 入门：如何管理 Unity 项目中的 NuGet 包？使用第三方 NuGet 包管理器——NuGetForUnity

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一、自行下载、解压、导入

下载依赖包含 .NETStandard 2.1 的 mqttnet.4.3.7.1207.nupkg。

最新的 5.0 只依赖 .net8.0 ， Unity 里面用不了

将下载好的文件后缀改为 zip ，并解压。

根据 Unity 中设置的 API 兼容性级别 ，找到对应的 lib 文件夹下的 dll 放到 Plugins 文件夹中。

F:\mqttnet.4.3.7.1207\lib\netstandard2.1\MQTTnet.dll

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二、安装 NuGetForUnity ，导入

去这里下载最新的Release
https://github.com/GlitchEnzo/NuGetForUnity

导入后，Unity 上方工具栏点击 NuGet / Manage NuGet Packages，找到对应版本的 MQTTnet ，Install

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三、代码示例

using System;
using System.Threading.Tasks;
using UnityEngine;
using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Exceptions;

public class MQTTManager : MonoBehaviour
{
    private IMqttClient mqttClient;
    public string brokerAddress = "broker.emqx.io"; // Change to your broker address
    public int brokerPort = 1883; // Default MQTT port
    public string topic = "testtopic/#";

    public MQTTnet.Formatter.MqttProtocolVersion mqttProtocolVersion = MQTTnet.Formatter.MqttProtocolVersion.V500;

    private void Start()
    {
        InitializeMQTTClient();
    }

    private async void InitializeMQTTClient()
    {
        mqttClient = new MqttFactory().CreateMqttClient();

        var options = new MqttClientOptionsBuilder()
            .WithClientId("UnityClient_" + Guid.NewGuid())
            .WithTcpServer(brokerAddress, brokerPort)
            .WithProtocolVersion(mqttProtocolVersion)
            .Build();


        mqttClient.ApplicationMessageReceivedAsync += MqttClient_ApplicationMessageReceivedAsync;
        mqttClient.ConnectedAsync += MqttClient_ConnectedAsync;
        mqttClient.DisconnectedAsync += MqttClient_DisconnectedAsync;

        try
        {
            await mqttClient.ConnectAsync(options);
            Debug.Log("Connected to MQTT broker.");
            SubscribeToTopic(topic); // Change to your topic
        }
        catch (MqttProtocolViolationException ex)
        {
            Debug.LogError($"Protocol error: {ex.Message}");
        }
        catch (Exception ex)
        {
            Debug.LogError($"Could not connect to MQTT broker: {ex.Message}");
        }
    }

    private Task MqttClient_DisconnectedAsync(MqttClientDisconnectedEventArgs arg)
    {
        return Task.CompletedTask;
    }

    private Task MqttClient_ConnectedAsync(MqttClientConnectedEventArgs arg)
    {
        return Task.CompletedTask;
    }

    private Task MqttClient_ApplicationMessageReceivedAsync(MqttApplicationMessageReceivedEventArgs arg)
    {
        Debug.Log(arg.ApplicationMessage.Topic);
        Debug.Log(arg.ApplicationMessage.ConvertPayloadToString());

        return Task.CompletedTask;
    }

    public async void PublishMessage(string topic, string message)
    {
        if (mqttClient.IsConnected)
        {
            var mqttMessage = new MqttApplicationMessageBuilder()
                .WithTopic(topic)
                .WithPayload(message)
                .WithQualityOfServiceLevel(MQTTnet.Protocol.MqttQualityOfServiceLevel.AtMostOnce)
                .WithRetainFlag()
                .Build();

            await mqttClient.PublishAsync(mqttMessage);
            Debug.Log($"Published message: {message} to topic: {topic}");
        }
        else
        {
            Debug.LogWarning("MQTT client is not connected.");
        }
    }

    public async void SubscribeToTopic(string topic)
    {
        if (mqttClient.IsConnected)
        {
            var topicFilter = new MqttTopicFilterBuilder()
                .WithTopic(topic)
                .Build();

            await mqttClient.SubscribeAsync(topicFilter);
            Debug.Log($"Subscribed to topic: {topic}");
        }
        else
        {
            Debug.LogWarning("MQTT client is not connected.");
        }
    }

    private async void OnApplicationQuit()
    {
        if (mqttClient != null)
        {
            await mqttClient.DisconnectAsync();
            Debug.Log("Disconnected from MQTT broker.");
        }
    }
}