当用户在SignalR Blazor中关闭浏览器时，如何获得通知

Question

我想在用户离开时向组中连接的所有用户发送通知。我该怎么做？

正如您在我的代码中看到的那样，我已经重写了OnDisconnectedAsync方法，但它仅在调用HubConnection.DisposeAsync();时有效。但如果我关闭浏览器或选项卡，它将不会起任何作用。

public override Task OnConnectedAsync()
{
Console.WriteLine("User Joined.");
return base.OnConnectedAsync();
}
public override Task OnDisconnectedAsync(Exception exception)
{
Console.WriteLine("User Left.");
return base.OnDisconnectedAsync(exception);
}

当浏览器关闭时，有什么方法可以得到通知吗？

Answer 1

您可以创建一个从CircuitHandler派生的服务类：

CircuitHandlerServices.cs

using Microsoft.AspNetCore.Components.Server.Circuits;
using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;
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)
{
Circuit circuitRemoved;
Circuits.TryRemove(circuit.Id, out circuitRemoved);
OnCircuitsChanged();
return base.OnCircuitClosedAsync(circuit, cancellationToken);
}
public override Task OnConnectionDownAsync(Circuit circuit, CancellationToken cancellationToken)
{
return base.OnConnectionDownAsync(circuit, cancellationToken);
}
public override Task OnConnectionUpAsync(Circuit circuit, CancellationToken cancellationToken)
{
return base.OnConnectionUpAsync(circuit, cancellationToken);
}

}

将服务添加到DI容器：

services.AddSingleton<CircuitHandler>(new CircuitHandlerService());

测试服务：

@page "/"
@using Microsoft.AspNetCore.Components.Server.Circuits
@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());
}
}

Answer 2

使用CircuitHandler

Blazor Server允许代码定义电路处理程序，该程序允许在更改用户电路状态时运行代码。电路处理程序是通过从CircuitHandler派生并在应用程序的服务容器中注册类来实现的。

public class TrackingCircuitHandler : CircuitHandler 
{
private HashSet<Circuit> circuits = new HashSet<Circuit>();
public override Task OnConnectionUpAsync(Circuit circuit, CancellationToken cancellationToken)
{
circuits.Add(circuit);
return Task.CompletedTask;
}
public override Task OnConnectionDownAsync(Circuit circuit, CancellationToken cancellationToken)
{
circuits.Remove(circuit);
return Task.CompletedTask;
}
public int ConnectedCircuits => circuits.Count;
}

使用DI 注册电路处理程序

services.AddSingleton<CircuitHandler, TrackingCircuitHandler>();