小编Vla*_*tov的帖子

我正在使用 MediatR 9.0.0 （带有 MediatR.Extensions.Microsoft.DependencyInjection 9.0.0）。我有这样的事件通知处理程序：

public class StatusChangedEventHandler : INotificationHandler<StatusChangedEvent>
{
    
   public StatusChangedEventHandler ()
   {
   }
    
   public async Task Handle(StatusChangedEvent evnt, CancellationToken cancellationToken)
   {
      //some code 
   }
}

该事件正在从另一个命令处理程序发布：

public class ChangeStatusCommandHandler : IRequestHandler<ChangeStatusCommand, bool>
    {
        ...
        private readonly IMediator _mediator;

        public ChangeStatusCommandHandler(...,IMediator mediator)
        {
            ...
            _mediator = mediator;
        }

        public async Task<bool> Handle(ChangeStatusCommand command, CancellationToken cancellationToken)
        {

            ...

            await _mediator.Publish(new StatusChangedEvent(int id, string message));

            ...
            
        }
    }

问题是 StatusChangedEventHandler.Handle 方法被多次调用 - 我注意到它似乎与 Startup.cs 中注册的命令处理程序的数量相关，例如

services.AddMediatR(typeof(CommandA));

=> 处理程序将被调用一次

services.AddMediatR(typeof(CommandA)); …