WPF Prism应用中MediatR LoggingBehavior未触发问题排查

问题场景 #

在WPF Prism应用中尝试通过MediatR管道机制实现请求日志功能，但自定义的LoggingBehavior始终未触发，相关代码如下：

DI容器配置 #

containerRegistry.Register(typeof(IPipelineBehavior<,>), typeof(LoggingBehavior<,>));
containerRegistry.RegisterSingleton<IMediator, Mediator>();

LoggingBehavior类 #

public class LoggingBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
{
    private readonly ILogger<LoggingBehavior<TRequest, TResponse>> _logger;

    public LoggingBehavior(ILogger<LoggingBehavior<TRequest, TResponse>> logger)
    {
        _logger = logger;
    }

    public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
    {
        _logger.LogInformation($"Handling {typeof(TRequest).Name}");

        var response = await next();

        _logger.LogInformation($"Handled {typeof(TResponse).Name}");

        return response;
    }
}

请求处理器 #

public class GetImportProjectDetailsQuery : IRequestHandler<GetImportProjectDetailsRequest, GetImportProjectDetailsResponse>
{
    private readonly IImportRepository _importRepository; 

    public GetImportProjectDetailsQuery(IImportRepository importRepository )
    {
        _importRepository = importRepository; 
    }

    public async Task<GetImportProjectDetailsResponse> Handle(GetImportProjectDetailsRequest request, CancellationToken cancellationToken)
    {
        // 业务逻辑代码
        return result;
    }
}

请求类型 #

public class GetImportProjectDetailsRequest : IRequest<GetImportProjectDetailsResponse>
{
    public string? Id { get; set; }
}

调用代码 #

private async Task<GetImportProjectDetailsResponse> GetImportProjectDetails(string projectId)
{
    var importProjectResult = await _mediator.Send(new GetImportProjectDetailsRequest {Id = projectId});

    return importProjectResult;
}

错误原因及修正方案 #

1. 核心错误：手动注册IMediator单例 #

手动注册IMediator为Singleton时，没有向Mediator的构造函数注入所需的IEnumerable<IPipelineBehavior<,>>集合，导致MediatR无法加载并执行你的LoggingBehavior。

2. 修正DI配置 #

移除手动注册IMediator的代码，让DI容器自动解析IMediator的实现（容器会自动注入所有已注册的IPipelineBehavior实例）：

// 保留管道行为注册
containerRegistry.Register(typeof(IPipelineBehavior<,>), typeof(LoggingBehavior<,>));
// 移除以下手动注册代码
// containerRegistry.RegisterSingleton<IMediator, Mediator>();

// 确保请求处理器已注册到容器
containerRegistry.Register<IRequestHandler<GetImportProjectDetailsRequest, GetImportProjectDetailsResponse>, GetImportProjectDetailsQuery>();

3. 额外注意事项 #

• 如果项目中有多个请求处理器，建议使用批量注册方式（例如通过程序集扫描），避免逐个注册的繁琐。
• 确保日志组件（如Serilog、NLog）已正确配置，避免因日志未输出导致误判行为未触发。

内容的提问来源于stack exchange，提问作者Peter Krämer