以下是一个使用Asp.Net Core的WebSocket的简单示例：

首先，在Startup.cs文件中，添加以下代码以启用WebSocket：

public void ConfigureServices(IServiceCollection services)
{
    services.AddWebSocketManager();
    // 添加其他服务配置
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseWebSockets();
    app.UseWebSocketServer();
    // 添加其他中间件配置
}

然后，创建一个WebSocket中间件WebSocketServerMiddleware.cs：

public class WebSocketServerMiddleware
{
    private readonly RequestDelegate _next;
    private readonly IWebSocketManager _webSocketManager;

    public WebSocketServerMiddleware(RequestDelegate next, IWebSocketManager webSocketManager)
    {
        _next = next;
        _webSocketManager = webSocketManager;
    }

    public async Task Invoke(HttpContext context)
    {
        if (context.WebSockets.IsWebSocketRequest)
        {
            WebSocket webSocket = await context.WebSockets.AcceptWebSocketAsync();

            // 处理WebSocket连接
            var socketId = _webSocketManager.AddSocket(webSocket);
            await _webSocketManager.HandleConnectionAsync(socketId);

            await Receive(webSocket, async (result, buffer) =>
            {
                if (result.MessageType == WebSocketMessageType.Text)
                {
                    await _webSocketManager.HandleMessageAsync(socketId, result, buffer);
                    return;
                }

                if (result.MessageType == WebSocketMessageType.Close)
                {
                    await _webSocketManager.HandleDisconnectedAsync(socketId);
                    return;
                }
            });
        }
        else
        {
            await _next(context);
        }
    }

    private async Task Receive(WebSocket webSocket, Action handleMessage)
    {
        var buffer = new byte[1024 * 4];

        while (webSocket.State == WebSocketState.Open)
        {
            var result = await webSocket.ReceiveAsync(buffer, CancellationToken.None);
            handleMessage(result, buffer);
        }
    }
}

接下来，创建一个WebSocket管理器WebSocketManager.cs：

public interface IWebSocketManager
{
    string AddSocket(WebSocket socket);
    Task HandleConnectionAsync(string socketId);
    Task HandleMessageAsync(string socketId, WebSocketReceiveResult result, byte[] buffer);
    Task HandleDisconnectedAsync(string socketId);
}

public class WebSocketManager : IWebSocketManager
{
    private ConcurrentDictionary _sockets = new ConcurrentDictionary();

    public string AddSocket(WebSocket socket)
    {
        var socketId = Guid.NewGuid().ToString();
        _sockets.TryAdd(socketId, socket);
        return socketId;
    }

    public async Task HandleConnectionAsync(string socketId)
    {
        // 处理新的WebSocket连接
        // 可以向客户端发送初始消息
        await SendMessageAsync(socketId, "Connected");
    }

    public async Task HandleMessageAsync(string socketId, WebSocketReceiveResult result, byte[] buffer)
    {
        // 处理接收到的消息
        var message = Encoding.UTF8.GetString(buffer, 0, result.Count);
        await SendMessageAsync(socketId, $"Received: {message}");
    }

    public async Task HandleDisconnectedAsync(string socketId)
    {
        // 处理WebSocket断开连接
        _sockets.TryRemove(socketId, out var socket);
        await socket.CloseAsync(WebSocketCloseStatus.NormalClosure, "Closed by the server", CancellationToken.None);
    }

    private async Task SendMessageAsync(string socketId, string message)
    {
        if (_sockets.TryGetValue(socketId, out var socket))
        {
            var buffer = Encoding.UTF8.GetBytes(message);
            await socket.SendAsync(buffer, WebSocketMessageType.Text, true, CancellationToken.None);
        }
    }
}

最后，在Startup.cs文件中添加WebSocket服务的扩展方法：

public static class WebSocketExtensions
{
    public static IServiceCollection AddWebSocketManager(this IServiceCollection services)
    {
        services.AddSingleton();
        return services;
    }

    public static IApplicationBuilder UseWebSocketServer(this IApplicationBuilder app)
    {
        app.UseMiddleware();
        return app;
    }
}

现在，你可以在控制器或其他地方注入IWebSocketManager，并使用它进行WebSocket通信。例如，在控制器中：

[ApiController]
[Route("api/[controller]")]
public class WebSocketController : ControllerBase
{
    private readonly IWebSocketManager _webSocketManager;

    public WebSocketController(IWebSocketManager webSocketManager)
    {
        _webSocketManager = webSocketManager;
    }

    [HttpGet]
    public async Task Get()
    {
        // 向所有连接的客户端发送消息