基于C#实现MQTT通信实战

    // 连接主机
    MqttFactory factory = new MqttFactory();
    _client = factory.CreateMqttClient();
    var options = new MqttClientOptionsBuilder().
        WithTcpServer(this.ipAddress.Text, Convert.ToInt32(this.port.Text))
        .WithClientId(this.clientId.Text)
        .Build();
    var result = await _client.ConnectAsync(options, CancellationToken.None);
    if (result.ResultCode == MqttClientConnectResultCode.Success)
    {
        this.log.Text = DateTime.Now.ToString() + "    连接成功" + Environment.NewLine + this.log.Text;
    }
    else
    {
        this.log.Text = DateTime.Now.ToString() + $"    连接失败，{result.ReasonString}" + Environment.NewLine + this.log.Text;
        return;
    }

    // 订阅消息
    var option = new MqttClientSubscribeOptions();
    MqttQualityOfServiceLevel level;
    switch (this.subscribeQos.SelectedIndex)
    {
        case 0:
            level = MQTTnet.Protocol.MqttQualityOfServiceLevel.AtMostOnce;
            break;
        case 1:
            level = MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce;
            break;
        case 2:
            level = MQTTnet.Protocol.MqttQualityOfServiceLevel.ExactlyOnce;
            break;
        default:
            throw new Exception("请选择服务质量");
    }
 
    option.TopicFilters = new List<MqttTopicFilter>()
    {
        new MqttTopicFilter()
        {
            Topic = this.subscribeTopic.Text,
            QualityOfServiceLevel = level
        }
    };
    this._client.SubscribeAsync(option, CancellationToken.None);
 
    // 将订阅的消息回显到日志区
    this._client.ApplicationMessageReceivedAsync += e =>
    {
        var task = Task.Factory.StartNew(() => {
            try
            {
                var array = e.ApplicationMessage.PayloadSegment.Array;
                if (array == null)
                {
                    return;
                }
 
                var str = Encoding.UTF8.GetString(array);
 
                // 跨线程更新UI
                Application.Current.Dispatcher.Invoke(() => {
                    this.log.Text = DateTime.Now.ToString() + "    收到消息：" + str + Environment.NewLine + this.log.Text;
                });
            }
            catch (Exception ex)
            {
                this.log.Text = DateTime.Now.ToString() + $"    {ex.Message}" + Environment.NewLine + this.log.Text;
            }
        });
 
        return task;
    };
 
    this.log.Text = DateTime.Now.ToString() + "    订阅成功" + Environment.NewLine + this.log.Text;

    var msg = new MqttApplicationMessage();
    msg.Topic = this.topic.Text;
    msg.PayloadSegment = Encoding.UTF8.GetBytes(this.msg.Text);
    msg.Retain = isSave.IsChecked??false;
    MqttQualityOfServiceLevel level;
    switch (this.publishQos.SelectedIndex)
    {
        case 0:
            level = MQTTnet.Protocol.MqttQualityOfServiceLevel.AtMostOnce;
            break;
        case 1:
            level = MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce;
            break;
        case 2:
            level = MQTTnet.Protocol.MqttQualityOfServiceLevel.ExactlyOnce;
            break;
        default:
            throw new Exception("请选择服务质量");
    }
    
    msg.QualityOfServiceLevel = level;
    var resultPublish = await _client.PublishAsync(msg, CancellationToken.None);
    if (resultPublish.IsSuccess == true)
    {
        this.log.Text = DateTime.Now.ToString() + "    发送成功" + Environment.NewLine + this.log.Text;
    }
    else
    {
        this.log.Text = DateTime.Now.ToString() + "    发送失败" + Environment.NewLine + this.log.Text;
    }