基于.net C# Socket WinForm MQTT 客户端开发

1、什么是MQTT？
　　MQTT（Message Queuing Telemetry Transport，消息队列遥测传输协议），是一种基于发布/订阅（publish/subscribe）模式的"轻量级"通讯协议，该协议构建于TCP/IP协议上，由IBM在1999年发布。MQTT最大优点在于，可以以极少的代码和有限的带宽，为连接远程设备提供实时可靠的消息服务。作为一种低开销、低带宽占用的即时通讯协议，使其在物联网、小型设备、移动应用等方面有较广泛的应用。

　　MQTT是一个基于客户端-服务器的消息发布/订阅传输协议。MQTT协议是轻量、简单、开放和易于实现的，这些特点使它适用范围非常广泛。在很多情况下，包括受限的环境中，如：机器与机器（M2M）通信和物联网（IoT）。其在，通过卫星链路通信传感器、偶尔拨号的医疗设备、智能家居、及一些小型化设备中已广泛使用。
（具体描述自行百度）

　　本文将基于.Net C# Socket WinForm MQTT 客户端开发，实现服务端连接，消息发布，消息订阅，取消订阅及接收服务端返回消息功能。

2、连接服务端

　　客户端连接服务端，启动异步接收服务端消息。

 1                     //连接选项
 2                     var option = new MQTT.MQTTClientOption()
 3                     {
 4                         ClientId = this.txtClientId.Text,
 5                         IpString = this.txtServer.Text,
 6                         Port = Convert.ToInt32(this.txtPort.Text),
 7                         UserName = this.txtUserName.Text,
 8                         Password = this.txtPassword.Text
 9                     };
10                     //实例客户端
11                     this.mqttClient = new MQTT.MQTTClient();
12                     this.mqttClient.ClientReceived += MqttClient_ClientReceived;
13                     var result = await this.mqttClient.ConnectAsync(option);
14                     if(result.State == false)
15                     {
16                         MessageBox.Show(result.Fail, "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);
17                         return;
18                     }
19                     //开始接收
20                     this.mqttClient.BeginReceive();

3、发布消息

　　客户端向服务端发送消息，主要包括主题，内容及消息质量。

　　发送消息程序

 1         private short _PacketId = 1;
 2         private async void BtnPublish_Click(object sender, EventArgs e)
 3         {
 4             this.btnPublish.Enabled = false;
 5             this.Cursor = Cursors.WaitCursor;
 6             try
 7             {
 8                 short qos = 0;
 9                 if (rdbLevel1.Checked)
10                     qos = 1;
11                 if (rdbLevel2.Checked)
12                     qos = 2;
13
14                 var data = new MQTT.PublishEntity()
15                 {
16                     Topic = this.txtTopic.Text,
17                     Reload = System.Text.Encoding.UTF8.GetBytes(this.txtContent.Text),
18                     Qos = qos,
19                     PacketId=_PacketId
20                 };
21                 var result = await this.mqttClient.PublishAsync(data,false);
22                 if(result.State == false)
23                 {
24                     this.AppendText("发送失败：" + result.Fail);
25                     return;
26                 }
27                 this._PacketId++;
28                 this.AppendText("发送成功，返回结果：" + result.Result);
29             }
30             finally
31             {
32                 this.btnPublish.Enabled = true;
33                 this.Cursor = Cursors.Default;
34             }
35         }

4、订阅消息

　　客户端订阅消息，主要包括过滤主题及消息质量。

　　订阅消息方法：

 1 private async void BtnSubscribe_Click(object sender, EventArgs e)
 2         {
 3             this.btnSubscribe.Enabled = false;
 4             this.Cursor = Cursors.WaitCursor;
 5
 6             try
 7             {
 8                 string fail = string.Empty;
 9
10                 short qos = 0;
11                 if (rdbQos1.Checked)
12                     qos = 1;
13                 if (rdbQos2.Checked)
14                     qos = 2;
15
16                 MQTT.SubscribeEntity entity = new MQTT.SubscribeEntity();
17                 entity.Filter = this.txtFilter.Text;
18                 entity.Qos = qos;
19
20                 this.AppendText("开始订阅...");
21                 //if (mqttClient.Subscribe(this.txtFilter.Text, qos, out result, out fail) == false)
22                 //{
23                 //    this.AppendText(fail);
24                 //    return;
25                 //}
26                 var result = await mqttClient.SubscribeAsync(entity.Filter,entity.Qos);
27                 if (result.State == false)
28                 {
29                     this.AppendText(result.Fail);
30                     return;
31                 }
32
33                 this.AppendText("订阅成功！返回结果：" + result.Result);
34                 MQTT.SubscribeHelper.Save(entity);
35
36                 DataRow drData = this.dtSubscribes.NewRow();
37                 drData["Id"] = entity.Id;
38                 drData["Filter"] = entity.Filter;
39                 drData["Qos"] = entity.Qos;
40                 drData["Count"] = 0;
41                 dtSubscribes.Rows.Add(drData);
42             }
43             finally
44             {
45                 this.btnSubscribe.Enabled = true;
46                 this.Cursor = Cursors.Default;
47             }
48         }

5、取消订阅

　　客户端取消某一订阅消息。双击订阅消息行，取消订阅消息。

　　取消订阅方法：

 1         private async void DataGridView1_CellDoubleClick(object sender, DataGridViewCellEventArgs e)
 2         {
 3             if (this.dataGridView1.CurrentCell == null)
 4                 return;
 5
 6             DataRowView drv = this.dataGridView1.CurrentRow.DataBoundItem as DataRowView;
 7             if (drv == null)
 8                 return;
 9
10             if (MessageBox.Show("确认取消当前选择：" + drv["Filter"].ToString() + " 订阅?", "确认", MessageBoxButtons.OKCancel, MessageBoxIcon.Question) != DialogResult.OK)
11                 return;
12             try
13             {
14                 this.AppendText("开始取消订阅...");
15                 var result = await mqttClient.UnSubscribeAsync(drv["Filter"].ToString());
16                 if (result.State == false)
17                 {
18                     this.AppendText(result.Fail);
19                     return;
20                 }
21                 this.AppendText("取消订阅成功！返回结果：" + result.Result);
22                 MQTT.SubscribeHelper.Delete(drv["Id"].ToString());
23                 this.dataGridView1.Rows.RemoveAt(this.dataGridView1.CurrentCell.RowIndex);
24             }
25             catch (Exception ex)
26             {
27                 this.AppendText("取消订阅异常：" + ex.ToString());
28             }
29
30         }

6、接收服务端消息

　　客户端接收服务端转发过来的消息。

1         private void MqttClient_ClientReceived(MQTT.MQTTClient client, MQTT.ReceiveResult receive)
2         {
3             if(receive.Data != null)
4                 this.AppendText("DataReceived state="+receive.State+" topic="+ receive.Data.Topic + " content=" + System.Text.Encoding.UTF8.GetString(receive.Data.Reload));
5             else if(receive.State)
6                 this.AppendText("DataReceived state=" + receive.State + " result=" + receive.Result);
7             else
8                 this.AppendText("DataReceived state=" + receive.State + " fail=" + receive.Fail);
9         }

至此，客户端工具主要功能简介完毕，不当之处，欢迎指正！

客户端下载地址（码云服务器）：https://gitee.com/ShiQuan25/full-product-management/raw/master/WinMQTTClient/WinMQTTClient.zip