1、什么是MQTT？
MQTT（Message Queuing Telemetry Transport，訊息佇列遙測傳輸協議），是一種基于發布/訂閱（publish/subscribe）模式的"輕量級"通訊協議，該協議構建于TCP/IP協議上，由IBM在1999年發布，MQTT最大優點在于，可以以極少的代碼和有限的帶寬，為連接遠程設備提供實時可靠的訊息服務，作為一種低開銷、低帶寬占用的即時通訊協議，使其在物聯網、小型設備、移動應用等方面有較廣泛的應用，
MQTT是一個基于客戶端-服務器的訊息發布/訂閱傳輸協議，MQTT協議是輕量、簡單、開放和易于實作的，這些特點使它適用范圍非常廣泛，在很多情況下，包括受限的環境中，如：機器與機器（M2M）通信和物聯網（IoT），其在，通過衛星鏈路通信傳感器、偶爾撥號的醫療設備、智能家居、及一些小型化設備中已廣泛使用，
（具體描述自行百度）
本文將基于.Net C# Socket WinForm MQTT 客戶端開發，實作服務端連接，訊息發布，訊息訂閱，取消訂閱及接收服務端回傳訊息功能，
2、連接服務端
客戶端連接服務端，啟動異步接收服務端訊息，
1 //連接選項 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 //實體客戶端 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 //開始接收 20 this.mqttClient.BeginReceive();
3、發布訊息
客戶端向服務端發送訊息，主要包括主題，內容及訊息質量，
發送訊息程式
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 = https://www.cnblogs.com/henxiao25/archive/2022/11/27/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("發送失敗：" + result.Fail); 25 return; 26 } 27 this._PacketId++; 28 this.AppendText("發送成功，回傳結果：" + result.Result); 29 } 30 finally 31 { 32 this.btnPublish.Enabled = true; 33 this.Cursor = Cursors.Default; 34 } 35 }
4、訂閱訊息
客戶端訂閱訊息，主要包括過濾主題及訊息質量，
訂閱訊息方法：
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("開始訂閱..."); 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("訂閱成功！回傳結果：" + result.Result); 34 MQTT.SubscribeHelper.Save(entity); 35 36 DataRow drData = https://www.cnblogs.com/henxiao25/archive/2022/11/27/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、取消訂閱
客戶端取消某一訂閱訊息，雙擊訂閱訊息行，取消訂閱訊息，
取消訂閱方法：
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("確認取消當前選擇：" + drv["Filter"].ToString() + " 訂閱?", "確認", MessageBoxButtons.OKCancel, MessageBoxIcon.Question) != DialogResult.OK) 11 return; 12 try 13 { 14 this.AppendText("開始取消訂閱..."); 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("取消訂閱成功！回傳結果：" + 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("取消訂閱例外：" + ex.ToString()); 28 } 29 30 }
6、接收服務端訊息
客戶端接收服務端轉發過來的訊息，
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，客戶端工具主要功能簡介完畢，不當之處，歡迎指正！
客戶端下載地址（碼云服務器）：https://gitee.com/ShiQuan25/full-product-management/raw/master/WinMQTTClient/WinMQTTClient.zip
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標籤：.NET技术
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