编写C#聊天程序后台及前台，，包含发送文本消息、发送图片、发送小文件、抖动等功能；

以下是一个简单的C#聊天程序后台及前台代码示例，包含发送文本消息、发送图片、发送小文件、抖动等功能：

后台代码：

using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;

namespace ChatServer
{
    public class Server
    {
        private static readonly List<Client> clients = new List<Client>();
        private static readonly TcpListener listener = new TcpListener(IPAddress.Any, 8888);

        public static void Start()
        {
            listener.Start();
            Console.WriteLine("Server started. Listening for connections...");

            while (true)
            {
                TcpClient tcpClient = listener.AcceptTcpClient();
                Client client = new Client(tcpClient);
                clients.Add(client);
                Console.WriteLine($"Client connected: {client.EndPoint}");

                Thread thread = new Thread(() => HandleClient(client));
                thread.Start();
            }
        }

        private static void HandleClient(Client client)
        {
            NetworkStream stream = client.TcpClient.GetStream();
            byte[] buffer = new byte[4096];
            int bytesRead;

            while (true)
            {
                try
                {
                    bytesRead = stream.Read(buffer, 0, buffer.Length);
                    if (bytesRead > 0)
                    {
                        string message = Encoding.UTF8.GetString(buffer, 0, bytesRead);
                        if (message.StartsWith("/send "))
                        {
                            string[] parts = message.Substring(6).Split(new[] { "|||" }, StringSplitOptions.None);
                            string messageType = parts[0];
                            string messageContent = parts[1];
                            switch (messageType)
                            {
                                case "text":
                                    Broadcast($"{client.UserName}: {messageContent}");
                                    break;
                                case "image":
                                    Broadcast($"{client.UserName} sent an image.");
                                    break;
                                case "file":
                                    Broadcast($"{client.UserName} sent a file.");
                                    break;
                            }
                        }
                        else if (message.StartsWith("/shake"))
                        {
                            Shake(client);
                        }
                        else if (message.StartsWith("/quit"))
                        {
                            Console.WriteLine($"Client disconnected: {client.EndPoint}");
                            clients.Remove(client);
                            Broadcast($"{client.UserName} has left the chat.");
                            break;
                        }
                        else
                        {
                            Console.WriteLine($"Received message from {client.EndPoint}: {message}");
                        }
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine($"Error: {ex.Message}");
                    clients.Remove(client);
                    Broadcast($"{client.UserName} has left the chat.");
                    break;
                }
            }
        }

        private static void Broadcast(string message)
        {
            byte[] buffer = Encoding.UTF8.GetBytes(message);
            foreach (Client client in clients)
            {
                client.TcpClient.GetStream().Write(buffer, 0, buffer.Length);
            }
        }

        private static void Shake(Client client)
        {
            byte[] buffer = Encoding.UTF8.GetBytes("/shake");
            client.TcpClient.GetStream().Write(buffer, 0, buffer.Length);
        }
    }

    public class Client
    {
        public TcpClient TcpClient { get; }
        public string EndPoint => TcpClient.Client.RemoteEndPoint.ToString();
        public string UserName { get; set; }

        public Client(TcpClient tcpClient)
        {
            TcpClient = tcpClient;
        }
    }
}

前台代码：

using System;
using System.Drawing;
using System.IO;
using System.Net.Sockets;
using System.Windows.Forms;

namespace ChatClient
{
    public partial class MainForm : Form
    {
        private readonly TcpClient client;
        private readonly NetworkStream stream;
        private readonly byte[] buffer = new byte[4096];

        public MainForm()
        {
            InitializeComponent();

            client = new TcpClient("localhost", 8888);
            stream = client.GetStream();

            SendUserName();
            StartListening();
        }

        private void SendUserName()
        {
            string userName = Prompt.ShowDialog("Enter your name:", "Chat Room");
            byte[] buffer = Encoding.UTF8.GetBytes(userName);
            stream.Write(buffer, 0, buffer.Length);
        }

        private void StartListening()
        {
            stream.BeginRead(buffer, 0, buffer.Length, ReadCallback, null);
        }

        private void ReadCallback(IAsyncResult ar)
        {
            int bytesRead = stream.EndRead(ar);
            if (bytesRead > 0)
            {
                string message = Encoding.UTF8.GetString(buffer, 0, bytesRead);
                if (message.StartsWith("/shake"))
                {
                    Shake();
                }
                else
                {
                    AppendMessage(message);
                }
            }

            StartListening();
        }

        private void SendMessage(string messageType, string messageContent)
        {
            string message = $"/send {messageType}|||{messageContent}";
            byte[] buffer = Encoding.UTF8.GetBytes(message);
            stream.Write(buffer, 0, buffer.Length);
        }

        private void AppendMessage(string message)
        {
            if (InvokeRequired)
            {
                Invoke(new Action(() => AppendMessage(message)));
            }
            else
            {
                chatTextBox.AppendText(message + Environment.NewLine);
            }
        }

        private void Shake()
        {
            if (InvokeRequired)
            {
                Invoke(new Action(() => Shake()));
            }
            else
            {
                Point originalLocation = Location;
                Random random = new Random();
                for (int i = 0; i < 10; i++)
                {
                    int offsetX = random.Next(-5, 6);
                    int offsetY = random.Next(-5, 6);
                    Location = new Point(originalLocation.X + offsetX, originalLocation.Y + offsetY);
                    System.Threading.Thread.Sleep(50);
                }
                Location = originalLocation;
            }
        }

        private void sendButton_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrWhiteSpace(messageTextBox.Text))
            {
                return;
            }

            if (imageRadioButton.Checked)
            {
                OpenFileDialog openFileDialog = new OpenFileDialog();
                openFileDialog.Filter = "Image files (*.jpg, *.jpeg, *.png, *.gif) | *.jpg; *.jpeg; *.png; *.gif";
                if (openFileDialog.ShowDialog() == DialogResult.OK)
                {
                    string fileName = Path.GetFileName(openFileDialog.FileName);
                    using (FileStream fileStream = new FileStream(openFileDialog.FileName, FileMode.Open))
                    {
                        using (BinaryReader binaryReader = new BinaryReader(fileStream))
                        {
                            byte[] fileData = binaryReader.ReadBytes((int)fileStream.Length);
                            SendMessage("image", $"{fileName}|||{Convert.ToBase64String(fileData)}");
                        }
                    }
                }
            }
            else if (fileRadioButton.Checked)
            {
                OpenFileDialog openFileDialog = new OpenFileDialog();
                if (openFileDialog.ShowDialog() == DialogResult.OK)
                {
                    string fileName = Path.GetFileName(openFileDialog.FileName);
                    using (FileStream fileStream = new FileStream(openFileDialog.FileName, FileMode.Open))
                    {
                        using (BinaryReader binaryReader = new BinaryReader(fileStream))
                        {
                            byte[] fileData = binaryReader.ReadBytes((int)fileStream.Length);
                            SendMessage("file", $"{fileName}|||{Convert.ToBase64String(fileData)}");
                        }
                    }
                }
            }
            else
            {
                SendMessage("text", messageTextBox.Text);
            }

            messageTextBox.Clear();
            messageTextBox.Focus();
        }

        private void MainForm_FormClosing(object sender, FormClosingEventArgs e)
        {
            byte[] buffer = Encoding.UTF8.GetBytes("/quit");
            stream.Write(buffer, 0, buffer.Length);
        }
    }

    public static class Prompt
    {
        public static string ShowDialog(string text, string caption)
        {
            Form prompt = new Form();
            prompt.StartPosition = FormStartPosition.CenterScreen;
            prompt.Size = new Size(300, 150);
            prompt.Text = caption;

            Label textLabel = new Label() { Left = 20, Top = 20, Text = text };
            TextBox textBox = new TextBox() { Left = 20, Top = 50, Width = 250 };
            Button okButton = new Button() { Text = "OK", Left = 150, Top = 80, Width = 75, DialogResult = DialogResult.OK };
            okButton.Click += (sender, e) => prompt.Close();

            prompt.Controls.Add(textLabel);
            prompt.Controls.Add(textBox);
            prompt.Controls.Add(okButton);
            prompt.AcceptButton = okButton;

            return prompt.ShowDialog() == DialogResult.OK ? textBox.Text : "";
        }
    }
}

使用方法：

1. 运行ChatServer.exe启动服务器；
2. 运行ChatClient.exe启动客户端；
3. 在客户端输入用户名并按下Enter键；
4. 在客户端输入消息并按下Send按钮，或选择发送图片或小文件；
5. 如果想抖动窗口，可以在客户端按下Shake按钮。

注意：该代码示例为演示用途，没有进行安全性和健壮性方面的优化，仅适用于学习和测试。在实际应用中，需要进行更多的检查和处理，以确保程序的安全和稳定。