段时间在使用MQTTnet，都说这个东西比较好,可是翻了翻网上没有例子给参考一下。
今天算是找到了，给高手的帖子做个宣传吧.
原网址如下：https://blog.csdn.net/chenlu5201314/article/details/94740765
由于GitHub上介绍的东西比较少，以我的水平真是不知道怎么用，先照葫芦画瓢，再看看怎么回事吧：
功能：
把订阅与发布做成一个类，还带有自动重连的功能
using System.Threading; using System.Threading.Tasks; using MQTTnet; using MQTTnet.Client; //客户端需要用到 using MQTTnet.Client.Options; //具体连接时需要用到的属性,ID的名称,要连接Server的名称,接入时用到的账号和密码,掉线时是否重新清除原有名称,还有许多... using MQTTnet.Packets; //这个没用上 using MQTTnet.Protocol; //这个也没用上 using MQTTnet.Client.Receiving; //接收 using MQTTnet.Client.Disconnecting; //断线 using MQTTnet.Client.Connecting; //连接
新建一个类：先写一下变量和一些字段
class HOSMQTT { private static MqttClient mqttClient = null; private static IMqttClientOptions options = null; private static bool runState = false; private static bool running = false; /// <summary> /// 服务器IP /// </summary> private static string ServerUrl = "182.61.51.85"; /// <summary> /// 服务器端口 /// </summary> private static int Port = 61613; /// <summary> /// 选项 - 开启登录 - 密码 /// </summary> private static string Password = "ruichi8888"; /// <summary> /// 选项 - 开启登录 - 用户名 /// </summary> private static string UserId = "admin"; /// <summary> /// 主题 /// <para>China/Hunan/Yiyang/Nanxian</para> /// <para>Hotel/Room01/Tv</para> /// <para>Hospital/Dept01/Room001/Bed001</para> /// <para>Hospital/#</para> /// </summary> private static string Topic = "China/Hunan/Yiyang/Nanxian"; /// <summary> /// 保留 /// </summary> private static bool Retained = false; /// <summary> /// 服务质量 /// <para>0 - 至多一次</para> /// <para>1 - 至少一次</para> /// <para>2 - 刚好一次</para> /// </summary> private static int QualityOfServiceLevel = 0; }
先看一下Start方法
public static void Start() { try { runState = true; Thread thread = new Thread(Work); //原帖中是这样写的 Thread thread = new Thread(new ThreadStart( Work)); thread.IsBackground = true; thread.Start(); } catch (Exception ex) { Console.WriteLine( "启动客户端出现问题:" + ex.ToString()); } }
没进入正题之前，先普及一下基本知识
C#的ThreadStart 和 Thread 多线程，new Thread(t1);和new Thread(new ThreadStart(t1));没有什么区别.前者是.net的写法，后者是C#的写法
具体请看下面的连接
https://www.cnblogs.com/rosesmall/p/8358348.html
进入整体，介绍连接方法 Work
private static void Work() { running = true; Console.WriteLine("Work >>Begin"); try { var factory = new MqttFactory(); //声明一个MQTT客户端的标准步骤 的第一步 mqttClient = factory.CreateMqttClient() as MqttClient; //factory.CreateMqttClient()实际是一个接口类型（IMqttClient）,这里是把他的类型变了一下 options = new MqttClientOptionsBuilder() //实例化一个MqttClientOptionsBulider
.WithTcpServer(ServerUrl, Port) .WithCredentials(UserId, Password) .WithClientId("XMan") .Build(); mqttClient.ConnectAsync(options); //连接服务器
//下面这些东西是什么，为什么要这么写，直到刚才我还是不懂，不过在GitHub的网址我发现了出处. mqttClient.ConnectedHandler = new MqttClientConnectedHandlerDelegate(new Func<MqttClientConnectedEventArgs, Task>(Connected)); mqttClient.DisconnectedHandler = new MqttClientDisconnectedHandlerDelegate(new Func<MqttClientDisconnectedEventArgs, Task>(Disconnected)); mqttClient.ApplicationMessageReceivedHandler = new MqttApplicationMessageReceivedHandlerDelegate(new Action<MqttApplicationMessageReceivedEventArgs>(MqttApplicationMessageReceived)); while (runState) { Thread.Sleep(100); } } catch(Exception exp) { Console.WriteLine(exp); } Console.WriteLine("Work >>End"); running = false; runState = false; }
先来看看MqttClient 类里面都有什么东西
需要实现的接口，如何实现，说重点！
在GitHub上有个地方进去看看就知道了‘
这个页面的最下方写着如何实现 https://github.com/chkr1011/MQTTnet/wiki/Upgrading-guide
private void Something() { mqttClient.ApplicationMessageReceivedHandler = new MqttApplicationMessageReceivedHandlerDelegate(OnAppMessage); mqttClient.ConnectedHandler = new MqttClientConnectedHandlerDelegate(OnConnected); mqttClient.DisconnectedHandler = new MqttClientDisconnectedHandlerDelegate(OnDisconnected); } private async void OnAppMessage(MqttApplicationMessageReceivedEventArgs e) { } private async void OnConnected(MqttClientConnectedEventArgs e) { } private async void OnDisconnected(MqttClientDisconnectedEventArgs e) { }
在开始Connected方法之前有必要看一下关于同步和异步的知识，
现学现卖简单说一下：
Task就是异步的调用，就在不影响主线程运行的另一个线程，但是他能像线程池一样更高效的利用现有的空闲线程
async必须用来修饰Task ,void，或者Task<TResult>, await是等待异步线程Task.Run()开始的后台线程执行完毕。
记住要是Task 实现异步功能，必须用 async 修饰，且async 与await成对出现。
详见下面大神写的大作:https://www.cnblogs.com/doforfuture/p/6293926.html
下面是什么意思？
mqttClient.ConnectedHandler = new MqttClientConnectedHandlerDelegate(new Func<MqttClientConnectedEventArgs, Task>(Connected));
MqttClientConnectedHandlerDelegate 这个实例实现了mqttClient.ConnectedHandler接口
new Func<MqttClientConnectedEventArgs, Task>(Connected) ，
使用Func委托传入MqttClientConnectedEventArgs类型的参数，返回的类型是Task,Task是一个类，这个类没有返回值，如果有返回值就是Task<TResult>。
是委托就要带一个方法取实现，这个方法就是Connected。
这句话的意思是，用MqttClientConnectedHandlerDelegate实现接口，同时使用委托取调用Connected的方法，并且给这个方法传入一个MqttClientConnectedEventArgs参数，
这个委托的返回值是Task（就是不需要返回类型的异步调用），这也就定义了Connected的类型必须是async Task。
好了来看下 Connected，这个函数什么意思
就是与服务器连接之后要干什么，订阅一个Topic，或几个Topic。连接之前已经连接了Connectasync(),如果断线还会重连，后面会提到。
这个就连接之后需要做的事----订阅！
private static async Task Connected(MqttClientConnectedEventArgs e) { try { List<TopicFilter> listTopic = new List<TopicFilter>(); if (listTopic.Count() <= 0) { var topicFilterBulder = new TopicFilterBuilder().WithTopic(Topic).Build(); listTopic.Add(topicFilterBulder); Console.WriteLine("Connected >>Subscribe " + Topic); } await mqttClient.SubscribeAsync(listTopic.ToArray()); Console.WriteLine("Connected >>Subscribe Success"); } catch (Exception exp) { Console.WriteLine(exp.Message); } }
TopicFilter是一个Topic详细信息的类
掉线的发生时会执行这个函数
private static async Task Disconnected(MqttClientDisconnectedEventArgs e) { try { Console.WriteLine("Disconnected >>Disconnected Server"); await Task.Delay(TimeSpan.FromSeconds(5)); try { await mqttClient.ConnectAsync(options); } catch (Exception exp) { Console.WriteLine("Disconnected >>Exception " + exp.Message); } } catch (Exception exp) { Console.WriteLine(exp.Message); } }
越写问题越多，这个为什么断线的时候会执行这个方法，这不是事件，只是接口！
怎么实现的？看了一下源码，一时只看了大概，这些功能的绑定都是在ConnectAsync的时候就完成了！
下面接收到消息的时候
/// <summary> /// 接收消息触发事件 /// </summary> /// <param name="e"></param> private static void MqttApplicationMessageReceived(MqttApplicationMessageReceivedEventArgs e) { try { string text = Encoding.UTF8.GetString(e.ApplicationMessage.Payload); string Topic = e.ApplicationMessage.Topic; string QoS = e.ApplicationMessage.QualityOfServiceLevel.ToString(); string Retained = e.ApplicationMessage.Retain.ToString(); Console.WriteLine("MessageReceived >>Topic:" + Topic + "; QoS: " + QoS + "; Retained: " + Retained + ";"); Console.WriteLine("MessageReceived >>Msg: " + text); } catch (Exception exp) { Console.WriteLine(exp.Message); } }
最后就是发布：一般会选择0，如果选择其他的情况在订阅端不在的时候，服务器可能会崩溃
/// <summary> /// /// 发布 /// <paramref name="QoS"/> /// <para>0 - 最多一次</para> /// <para>1 - 至少一次</para> /// <para>2 - 仅一次</para> /// </summary> /// <param name="Topic">发布主题</param> /// <param name="Message">发布内容</param> /// <returns></returns> public static void Publish( string Topic,string Message) { try { if (mqttClient == null) return; if (mqttClient.IsConnected == false) mqttClient.ConnectAsync(options); if (mqttClient.IsConnected == false) { Console.WriteLine("Publish >>Connected Failed! "); return; } Console.WriteLine("Publish >>Topic: " + Topic + "; QoS: " + QualityOfServiceLevel + "; Retained: " + Retained + ";"); Console.WriteLine("Publish >>Message: " + Message); MqttApplicationMessageBuilder mamb = new MqttApplicationMessageBuilder() .WithTopic(Topic) .WithPayload(Message).WithRetainFlag(Retained); if (QualityOfServiceLevel == 0) { mamb = mamb.WithAtMostOnceQoS(); } else if (QualityOfServiceLevel == 1) { mamb = mamb.WithAtLeastOnceQoS(); } else if (QualityOfServiceLevel == 2) { mamb = mamb.WithExactlyOnceQoS(); } mqttClient.PublishAsync(mamb.Build()); } catch (Exception exp) { Console.WriteLine("Publish >>" + exp.Message); } }
重点补充一下：
这两天验证的时候发现，对于MQTT服务器来说客户端的用户名必须是唯一的，
举例：同一台电脑上，两个程序同时发布(publish)到一个MQTT服务器，必须设置两个不同的ClientId，否则只有一个能连接上。
Paho的使用：
具体说明也可以看这位高手的：
https://blog.csdn.net/weixin_42133779/article/details/80226633
只是有一点需要强调以下：
Paho的目录不要太深，之前我就是三层文件夹下面，结果无法运行。一直提示 error code=13
没办法把他放在D盘的根目录下就可以了
纸上得来终觉浅，要改造成自己想要的些东西，还要花些功夫！不过这已经很好了！谢谢各位高手的贡献
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