如何使用实时（SignalR）更新数据

Question

I am writing to seek help, in regards creating a real-time data update using SignalR. I am currently having issue on the client-side, where I am unable to render the data content.

I have a tested the query command and it seems to be returning data. This leads me to believe, that my client-side code, maybe incorrect.

<script src="~/Scripts/jquery-1.8.2.min.js" type="text/javascript" ></script>
<script src="~/Scripts/jquery.signalR-2.0.1.min.js" type="text/javascript" ></script>
<script src="~/signalr/hubs" type="text/javascript" ></script>
<script type="text/javascript">
$(function () {
    // Declare a proxy to reference the hub.          
    var notifications = $.connection.NotificationHub;
    // Create a function that the hub can call to broadcast messages.
    notifications.client.recieveNotification = function (role, descrip) {
        // Add the message to the page.                    
        $('#spanNewMessages').text(role);
        $('#spanNewCircles').text(descrip);

    };
    // Start the connection.
   $.connection.hub.start().done(function () {
        notifications.server.sendNotifications(function () {
            alert("does it work");
            });
    }).fail(function (e) {
        alert(e);
    });
 </script>
 <h1>New Notifications</h1>
 <div>
<b>New <span id="spanNewMessages"></span> role.</b><br />
<b>New<span id="spanNewCircles"></span> descrip.</b><br />

 </div>

Hub Class:

  [HubName("NotificationHub")]
  public class notificationHub : Hub
  {
    string role = "";
    string descrip = "";

    [HubMethodName("sendNotifications")]
    public void SendNotifications()
    {
        using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["dummyConnectionString"].ConnectionString))
        {
            string query = "SELECT [role],[description] FROM [dbo].[User]";
            connection.Open();
            using (SqlCommand command = new SqlCommand(query, connection))
            {                  
                command.Notification = null;                
                DataTable dt = new DataTable();
                SqlDependency dependency = new SqlDependency(command);
                dependency.OnChange += new OnChangeEventHandler(dependency_OnChange);
                if (connection.State == ConnectionState.Closed)
                    connection.Open();                
                var reader = command.ExecuteReader();
                dt.Load(reader);
                if (dt.Rows.Count > 0)
                {
                    role = dt.Rows[0]["role"].ToString();
                    descrip = dt.Rows[0]["description"].ToString();

                }
            }  
        }

     Clients.All.RecieveNotification(role, descrip);
    }
    private void dependency_OnChange(object sender, SqlNotificationEventArgs e)
    {
        if (e.Type == SqlNotificationType.Change)
        {
            notificationHub nHub = new notificationHub();
            nHub.SendNotifications();
        }
    }

}

StartUp CLass:

 using Microsoft.Owin;
 using Owin;
 using WebApplication2;

 namespace WebApplication2
 {
   public class Startup
    {
       public void Configuration(IAppBuilder app)
       {
        app.MapSignalR();
       }
    }
  }

Could anyone, please provide some assistant, to where I may be going wrong with this task. Thank you.

Answer 1

I mocked up your app. Your issue was you are returning a string from your hub action:

public string SendNotifications()
{
    return context.Clients.All.RecieveNotification(role, descrip);
}

this should be void (you aren't returning anything, but actually calling the clients), and you also don't need to use GlobalHost to get the context here, only when the context isn't available (IE calling the hub from the server). Try making these changes:

[HubMethodName("sendNotifications")]
public void SendNotifications()
{
    //using...

    //IHubContext context = GlobalHost.ConnectionManager.GetHubContext<notificationHub>();
    //return context.Clients.All.RecieveNotification(role, descrip);

    Clients.All.RecieveNotification(role, descrip);
}

Put a breakpoint at Clients.All... and see if it is being triggered. Let me know if these updates fix your issue.