Detect client closing connection Blazor

Question

I have a loop that I have got running the whole time the client is on the page but I got no way to close the loop so that always remains running even when the user already disconnected. Is there a lifecycle method that runs when the user closes the connection? or is there a different way?

Answer 1

I'm not sure just implementing the IDisposable Interface can help you here, but implementing the Blazor Server circuit handler may. I vaguely recall that a similar question to yours was asked in stackoverflow... the OP tried to implement the IDisposable Interface, but to no avail. I've answered once or twice that question and a follow up one...I'm posting the code from my answer, and I hope this helps you...

CircuitHandlerService.cs

using Microsoft.AspNetCore.Components.Server.Circuits;
using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;


namespace BlazorCircuitHandler.Services
{
  public class CircuitHandlerService : CircuitHandler 
  {
    public ConcurrentDictionary<string, Circuit> Circuits { get; set; }
    public event EventHandler CircuitsChanged;

    protected virtual void OnCircuitsChanged()
    => CircuitsChanged?.Invoke(this, EventArgs.Empty);

    public CircuitHandlerService()
    {
        Circuits = new ConcurrentDictionary<string, Circuit>();
    }

    public override Task OnCircuitOpenedAsync(Circuit circuit, 
                              CancellationToken cancellationToken)
    {
        Circuits[circuit.Id] = circuit;
        OnCircuitsChanged();
        return base.OnCircuitOpenedAsync(circuit, cancellationToken);
    }

    public override Task OnCircuitClosedAsync(Circuit circuit, 
                  CancellationToken cancellationToken)
    {
        Console.WriteLine("OnCircuitClosedAsync");
        Circuit circuitRemoved;
        Circuits.TryRemove(circuit.Id, out circuitRemoved);
        OnCircuitsChanged();
        return base.OnCircuitClosedAsync(circuit, cancellationToken);
    }

    public override Task OnConnectionDownAsync(Circuit circuit, 
                    CancellationToken cancellationToken)
    {
        Console.WriteLine("OnConnectionDownAsync");
        return base.OnConnectionDownAsync(circuit, cancellationToken);
    }

    public override Task OnConnectionUpAsync(Circuit circuit, 
        CancellationToken cancellationToken)
    {
        return base.OnConnectionUpAsync(circuit, cancellationToken);
    }

  }
 }

Usage

@page "/"

@using Microsoft.AspNetCore.Components.Server.Circuits
@using BlazorCircuitHandler.Services

@inject CircuitHandler circuitHandler
@implements IDisposable



 <h1>Hello, world!</h1>

 Welcome to your new app.

<p>
 Number of Circuits: @((circuitHandler as 
    BlazorCircuitHandler.Services.CircuitHandlerService).Circuits.Count)
<ul>
    @foreach (var circuit in (circuitHandler as 
          BlazorCircuitHandler.Services.CircuitHandlerService).Circuits)
    {
        <li>@circuit.Key</li>
    }
</ul>
</p>

@code {

protected override void OnInitialized()
{
      // register event handler
    (circuitHandler as CircuitHandlerService).CircuitsChanged += 
                                          HandleCircuitsChanged;
}

public void Dispose()
{
    // unregister the event handler when the component is destroyed
    (circuitHandler as CircuitHandlerService).CircuitsChanged -= 
                                             HandleCircuitsChanged;
}

public void HandleCircuitsChanged(object sender, EventArgs args)
{
    // notify the UI that the state has changed
    InvokeAsync(() => StateHasChanged());
 }
}

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
   // ........ .....
   services.AddSingleton<CircuitHandler>(new CircuitHandlerService());
}