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How do you build Blazor apps with SignalR?

Platform: Blazor| Category: General

Blazor Server

In server code, configure SignalR in the Startup.cs class file as follows.

public void ConfigureServices(IServiceCollection services)
{
    ... ... ... ...
    services.AddSignalR();
    ... ... ... ...

}


public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    ... ... ... ...
    app.UseSignalR(routes => routes.MapHub<Blazor.NetCore.Server.SignalRHub.SignalRHub>("/signalRHub"));
    ... ... ... ...
}

And then create a SignalR hub class as follows.

    public class SignalRHub : Hub
    {
        public override Task OnConnectedAsync()
        {
            Clients.All.SendAsync("ReceiveMessage", "system", $"{Context.ConnectionId} joined the conversation");
            return base.OnConnectedAsync();
        }
        public void SendMessage(string name, string message)
        {
            Clients.All.SendAsync("ReceiveMessage", name, message);
        }

        public override Task OnDisconnectedAsync(System.Exception exception)
        {
            Clients.All.SendAsync("ReceiveMessage", "system", $"{Context.ConnectionId} left the conversation");
            return base.OnDisconnectedAsync(exception);
        }
    }

Blazor client

Create a Blazor app and add the package Blazor.Extensions.SignalR to the client. Then write the code to connect the Hub and event handler as follows.

@page "/signalr"
@using Blazor.Extensions
<div class="container">
    <input type="text" id="user" class="form-control" @bind="@userName" placeholder="User Name" /><br />
    <input type="text" id="message" class="form-control" @bind="@Message" placeholder="Message" /> <br />
    <input type="button" id="sendMessage" value="Send" class="btn btn-primary" @onclick="@SendMessage" />
    <ul id="discussion">
        @foreach (var message in messages)
        {
            <li>@message</li>
        }
    </ul>
</div>

@code {
    HubConnection connection;
    string userName = "";
    string Message = "";
    IList<string> messages = new List<string>();

    protected override async Task OnInitializedAsync()
    {
        connection = new HubConnectionBuilder().WithUrl("/signalRHub").Build();
        connection.On<string, string>("receiveMessage", this.ReceiveMessage);
        await connection.StartAsync();
    }

    Task ReceiveMessage(string name, string message)
    {
        messages.Add(name + " : " + message);
        StateHasChanged();
        return Task.CompletedTask;
    }

    async Task SendMessage()
    {
        await connection.InvokeAsync("SendMessage", userName, Message);
        Message = "";
    }
}
  1. OnInitializedAsync method, connect to the Web API.
  2. ReceiveMessage method, used in the SignalRHub class.
  3. ReceiveMessage method, concatenate the name and message parameters, and append them to a list.

The StateHasChanged method will update the bindings in the HTML. The SendMessage method will invoke the Send method in the hub with name and message parameters.

Reference link: https://docs.microsoft.com/en-us/aspnet/core/tutorials/signalr-blazor-webassembly?view=aspnetcore-3.1&tabs=visual-studio#add-the-signalr-client-library

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