Can't call client method from server - asp.net

Question

I'm trying to use SignalR to broadcast a message from the server to the client without the client triggering the message. From tutorials that I've seen, defining a method in the client, like so:
signalRConnection.client.addNewMessage = function(message) {
console.log(message);
};
should allow the following hub code to be used on the server:
public async Task SendMessage(string message)
{
await Clients.All.addNewMessage("Hey from the server!");
}
However, the Clients.All.addNewMessage call causes an error in the C# compiler:
'IClientProxy' does not contain a definition for 'addNewMessage' and no accessible extension method 'addNewMessage' accepting a first argument of type 'IClientProxy' could be found (are you missing a using directive or an assembly reference?)
How do I fix this? The server code is contained within the hub.

Answer 1

This is because you are using ASP.NET Core SignalR but you are calling client method following ASP.NET MVC SignalR. In ASP.NET Core SignalR you have to call the client method as follows:
public async Task SendMessage(string message)
{
await Clients.All.SendAsync("AddNewMessage", message); // here `AddNewMessage` is the method name in the client side.
}
It showing your client side code is also for ASP.NET MVC SignalR. For ASP.NET Core SignalR it should be as follows:
"use strict";
var connection = new signalR.HubConnectionBuilder().withUrl("/chatHub").build();
connection.on("AddNewMessage", function (message) {
// do whatever you want to do with `message`
});
connection.start().catch(function (err) {
return console.error(err.toString());
});
And In the Startup class SignalR setup should be as follows:
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
public void ConfigureServices(IServiceCollection services)
{
services.Configure<CookiePolicyOptions>(options =>
{
// This lambda determines whether user consent for non-essential cookies is needed for a given request.
options.CheckConsentNeeded = context => true;
options.MinimumSameSitePolicy = SameSiteMode.None;
});
services.AddMvc()
.SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
services.AddSignalR(); // Must add this
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Error");
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseCookiePolicy();
app.UseSignalR(routes =>
{
routes.MapHub<ChatHub>("/chatHub"); // Here is configuring for `ChatHub`
});
app.UseMvc();
}
}
Please follow Get started with ASP.NET Core SignalR this tutorial if you face further problem.