添加项目文件。

App.config

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+<?xml version="1.0" encoding="utf-8" ?>
+<configuration>
+    <startup> 
+        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.2" />
+    </startup>
+</configuration>

Program.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace SocketSingleSend
+{
+    class Program
+    {
+        private const string ANSWER_FLAG = ">>OK<<";
+        private const int MAX_BYTE_SIZE = 256;
+        static readonly IPAddress localIP = Dns.GetHostByName(Dns.GetHostName()).AddressList[0];
+        static readonly int PORT = 10019;
+        static readonly int AS_PORT = 11019;
+
+        static Socket udpSender;
+        static Socket udpReceiver;
+
+        static void Main(string[] args)
+        {
+            Console.WriteLine("1: Send ;\r\n2: Receive ;");
+            Console.WriteLine("Make a choice to do:");
+
+            string choice = Console.ReadLine();
+            if (choice == "1")
+            {
+                //do Send
+                IPAddress targetIP = null;
+                bool flag = false;
+                while (!flag)
+                {
+                    Console.WriteLine("Enter the other side's IP:");
+                    try
+                    {
+                        targetIP = IPAddress.Parse(Console.ReadLine());
+                        flag = true;
+                    }
+                    catch (Exception ex)
+                    {
+                        Console.WriteLine(ex.Message);
+                    }
+                }
+                Console.WriteLine("Write down your text:");
+                Console.WriteLine("-----------------------------------");
+                string str = null;
+                do
+                {
+                    str = Console.ReadLine();
+                    if (str.Length > (MAX_BYTE_SIZE / 2 - 2))
+                    {
+                        Console.WriteLine("<<<<<<<<<<<Too Long!");
+                        continue;
+                    }
+                    if (str.Length == 0)
+                    {
+                        Console.WriteLine("<<<<<<<<<<<Can not be empty!");
+                        continue;
+                    }
+                    if (!SendText(str, targetIP))
+                        Console.WriteLine("<<<<<<<<<<<The other side may not have received!");
+                } while (str != "exit");
+            }
+            else if (choice == "2")
+            {
+                //do Receive
+                Console.WriteLine("Local IP is: " + localIP);
+                Console.WriteLine("Waiting to receive the Msg...");
+                Console.WriteLine("-----------------------------------");
+                string msg = null;
+                do
+                {
+                    msg = ReceiveText(localIP);
+                    if (msg != null)
+                        Console.WriteLine(msg);
+                } while (msg != "exit");
+            }
+            udpReceiver?.Close();
+            udpSender?.Close();
+        }
+
+        static string ReceiveText(IPAddress listenIP)
+        {
+            IPEndPoint listenIPE = new IPEndPoint(listenIP, PORT);
+            IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
+            EndPoint remoteIPE = sender;
+            //UDP Mode
+            string receiveStr = UDPReceive(listenIPE, ref remoteIPE);
+            if (receiveStr != null)
+            {
+                //Send answer
+                IPEndPoint answerIPE = (IPEndPoint)remoteIPE;
+                answerIPE.Port = AS_PORT;
+                int count = 3;
+                while (count > 0)
+                {
+                    count--;
+                    if (UDPSend(ANSWER_FLAG, answerIPE))
+                        break;
+                }
+            }
+            return receiveStr;
+        }
+
+        static bool SendText(string str, IPAddress targetIP)
+        {
+            IPEndPoint targetIPE = new IPEndPoint(targetIP, PORT);
+            IPEndPoint answerIPE = new IPEndPoint(localIP, AS_PORT);
+            IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
+            EndPoint remoteIPE = sender;
+            //UDP Mode
+            if (UDPSend(str, targetIPE))
+            {
+                //Receive answer
+                if (UDPReceive(answerIPE, ref remoteIPE, false) == ANSWER_FLAG)
+                    return true;
+            }
+            return false;
+        }
+
+        static bool UDPSend(string str, EndPoint targetIPE)
+        {
+            if (udpSender == null)
+            {
+                udpSender = new Socket(AddressFamily.InterNetwork,
+                SocketType.Dgram, ProtocolType.Udp);
+                udpSender.SendTimeout = 800;
+            }
+
+            try
+            {
+                byte[] strByte = Encoding.UTF8.GetBytes(str);
+                int sendLen = udpSender.SendTo(strByte, SocketFlags.None, targetIPE);
+                if (sendLen == strByte.Length)
+                    return true;
+            }
+            catch { }
+            return false;
+        }
+
+        static string UDPReceive(EndPoint listenIPE, ref EndPoint remoteIPE, bool blocked = true)
+        {
+            if (udpReceiver == null)
+            {
+                //Receive_Socket的首次创建导致错过Answer信号的接收-------提升Socket创建顺序
+                //answerReceive网络缓冲区的旧数据导致收到“假Answer”------添加Answer校对
+                udpReceiver = new Socket(AddressFamily.InterNetwork,
+                SocketType.Dgram, ProtocolType.Udp);
+                udpReceiver.Bind(listenIPE);
+                if (!blocked)
+                    udpReceiver.ReceiveTimeout = 2500;
+            }
+
+            try
+            {
+                byte[] strByte = new byte[MAX_BYTE_SIZE];
+                int receiveLen = udpReceiver.ReceiveFrom(strByte,
+                    SocketFlags.None, ref remoteIPE);
+                if (receiveLen > 0)
+                    return Encoding.UTF8.GetString(strByte, 0, receiveLen);
+            }
+            catch { }
+            return null;
+        }
+
+    }
+}

Properties/AssemblyInfo.cs

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+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+// 有关程序集的一般信息由以下
+// 控制。更改这些特性值可修改
+// 与程序集关联的信息。
+[assembly: AssemblyTitle("SocketSingleSend")]
+[assembly: AssemblyDescription("")]
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyCompany("")]
+[assembly: AssemblyProduct("SocketSingleSend")]
+[assembly: AssemblyCopyright("Copyright ©  2019")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCulture("")]
+
+// 将 ComVisible 设置为 false 会使此程序集中的类型
+//对 COM 组件不可见。如果需要从 COM 访问此程序集中的类型
+//请将此类型的 ComVisible 特性设置为 true。
+[assembly: ComVisible(false)]
+
+// 如果此项目向 COM 公开，则下列 GUID 用于类型库的 ID
+[assembly: Guid("10f1df60-2525-41d6-8d30-ce0c22c0332c")]
+
+// 程序集的版本信息由下列四个值组成: 
+//
+//      主版本
+//      次版本
+//      生成号
+//      修订号
+//
+// 可以指定所有值，也可以使用以下所示的 "*" 预置版本号和修订号
+// 方法是按如下所示使用“*”: :
+// [assembly: AssemblyVersion("1.0.*")]
+[assembly: AssemblyVersion("1.0.0.0")]
+[assembly: AssemblyFileVersion("1.0.0.0")]

SocketSingleSend.csproj

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+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
+  <PropertyGroup>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <ProjectGuid>{10F1DF60-2525-41D6-8D30-CE0C22C0332C}</ProjectGuid>
+    <OutputType>Exe</OutputType>
+    <RootNamespace>SocketSingleSend</RootNamespace>
+    <AssemblyName>SocketSingleSend</AssemblyName>
+    <TargetFrameworkVersion>v4.6.2</TargetFrameworkVersion>
+    <FileAlignment>512</FileAlignment>
+    <AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects>
+    <Deterministic>true</Deterministic>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
+    <PlatformTarget>AnyCPU</PlatformTarget>
+    <DebugSymbols>true</DebugSymbols>
+    <DebugType>full</DebugType>
+    <Optimize>false</Optimize>
+    <OutputPath>bin\Debug\</OutputPath>
+    <DefineConstants>DEBUG;TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
+    <PlatformTarget>AnyCPU</PlatformTarget>
+    <DebugType>pdbonly</DebugType>
+    <Optimize>true</Optimize>
+    <OutputPath>bin\Release\</OutputPath>
+    <DefineConstants>TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <ItemGroup>
+    <Reference Include="System" />
+    <Reference Include="System.Core" />
+    <Reference Include="System.Xml.Linq" />
+    <Reference Include="System.Data.DataSetExtensions" />
+    <Reference Include="Microsoft.CSharp" />
+    <Reference Include="System.Data" />
+    <Reference Include="System.Net.Http" />
+    <Reference Include="System.Xml" />
+  </ItemGroup>
+  <ItemGroup>
+    <Compile Include="Program.cs" />
+    <Compile Include="Properties\AssemblyInfo.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="App.config" />
+  </ItemGroup>
+  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+</Project>

SocketSingleSend.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio 15
+VisualStudioVersion = 15.0.28307.136
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SocketSingleSend", "SocketSingleSend.csproj", "{10F1DF60-2525-41D6-8D30-CE0C22C0332C}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{10F1DF60-2525-41D6-8D30-CE0C22C0332C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{10F1DF60-2525-41D6-8D30-CE0C22C0332C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{10F1DF60-2525-41D6-8D30-CE0C22C0332C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{10F1DF60-2525-41D6-8D30-CE0C22C0332C}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {AEDFDC66-2A93-4E14-B270-5554BCE31708}
+	EndGlobalSection
+EndGlobal