c# - 事件处理器 ASP.NET CORE

Question

我在 ASP.NET CORE 中有一个项目。我想在 ExchangeService 类的 RejectExchange 方法完成之前调用一个方法(将来有几种方法)。所以我阅读了 EventHandlers 来做到这一点，但我不知道应该在哪里将方法分配给委托(delegate)。我有 ExchangeService 类:

public class ExchangeService : IExchange
{
    private readonly SocialNetworkContext _context;
    private readonly IUser _userService;
    private readonly IItem _itemService;
    private readonly IExchangeRequestNotification _exchangeRequestNotificationService;

    public event EventHandler<Exchange> ExchangeRejecting;

    protected virtual void OnExchangeRejecting(Exchange exchange)
    {
        ExchangeRejecting?.Invoke(this, exchange);
    }

    public void RejectExchange(int id)
    {
        var exchange = GetById(id);

        OnExchangeRejecting(exchange);

        Delete(exchange);
    }

    public ExchangeService(SocialNetworkContext context, IUser userService, IItem itemService, IExchangeRequestNotification exchangeRequestNotificationService)
    {
        _context = context;
        _userService = userService;
        _itemService = itemService;
        _exchangeRequestNotificationService = exchangeRequestNotificationService;            
    }
}

我想删除关于交换的通知，在交换被删除之前，在 ExchangeRequestNorificationService 中，所以我创建了方法 OnExchangeRejecting:

public class ExchangeRequestNotificationService : IExchangeRequestNotification
{
    private readonly SocialNetworkContext _context;
    private readonly IUser _userService;

    public ExchangeRequestNotificationService(SocialNetworkContext context, IUser userService)
    {
        _context = context;
        _userService = userService;
    }

    public void OnExchangeRejecting(object source, Exchange exchange) => Delete(GetByExchangeId(exchange.Id));    

    public void Delete(ExchangeRequestNotification exchangeRequestNotification)
    {
        _context.Remove(exchangeRequestNotification);
        _context.SaveChanges();
    }
}

一切都很好，但我不明白我必须在哪里将方法分配给委托(delegate)。我有 ExchangeController，我在其中使用依赖项注入(inject)并将 IExchangeService 传递给构造函数，然后我将方法分配给委托(delegate):

public ExchangeController(IExchange exchangeService, IExchangeRequestNotification exchangeRequestNotification, IChat chatService)
    {
        _exchangeService = exchangeService;
        _exchangeRequestNotificationService = exchangeRequestNotification;
        exchangeService.ExchangeRejecting += _exchangeRequestNotificationService.OnExchangeRejecting;
        exchangeService.ExchangeRejecting += chatService.OnExchangeRejecting;
    }

但我觉得不对，因为在这个controller中我真的不需要ExchangeRequestNotificationService和ChatService(它也有方法OnExchangeRejecting)，我只需要ExchangeService。 ExchangeRequestNotificationService 仅传递给 Controller ​​以将方法分配给方法 OnRejectingExchange 上的委托(delegate)，并且在未来它会更糟(注入(inject)更多不需要的服务)。

我的问题是我应该在哪里明确地将方法分配给委托(delegate)？对不起我的英语，我希望你能理解我的问题:)

Answer 1

我一直在问自己同样的问题，并且看到了您关于 stackoverflow 的帖子。由于在网上没有找到解决方案，我尝试自己解决。

对于该解决方案，我使用库 Autofac 作为 DI 提供程序并配置了我的服务，它通过 Autofac 的生命周期事件公开了一个 EventHandler。

例子:

builder.RegisterType<MyService>().InstancePerRequest().OnActivated(e =>
{
    var dep = e.Context.Resolve<MyEventHandler>();
    e.Instance.EntitySaved += dep.OnEntitySaved;
});

所以我可以保证无论我的服务注入(inject)到哪里，EventHandler 总是被注册。我选择了 OnActivated 生命周期事件而不是 OnActivating 以避免循环依赖问题；例如如果 MyService 应该由 EventHandler 间接使用。

最好的问候，丹尼尔