AfterMap使用IMappingAction和IHttpContextAccessor抛出错误

Question

我按照例子找到了here。我有一个课程如下：

```public class FileServiceRequestMappingAction：IMappingAction {private readonly IHttpContextAccessor _httpContextAccessor;

    public FileServiceRequestMappingAction(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public void Process(FileServiceRequest source, FileSearchRequest destination)
    {
        try
        {
            destination.Filter = "somevalue";

            var storageType = "somestoragetype";

            if (_httpContextAccessor.HttpContext.Request.Path.Value.ToLower().Contains("/patha/"))
            {
                storageType = "someothertypeofstorage";
            }

            if (!string.IsNullOrWhiteSpace(destination.Filter))
            {
                destination.Filter += $" and storageType eq {storageType}";
            }
            else
            {
                destination.Filter += $"storageType eq {storageType}";
            }
        }
        catch (Exception ex)
        {
            throw new TranslationException($"Error in filter. {ex.Message}");
        }
    }
}

```

在我的创业公司，我有：

services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
services.AddAutoMapper(typeof(FileServiceRequestMappingAction).Assembly);

当我启动应用程序并执行我的api查询调用地图时，我收到以下错误：

   at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor)
   at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
   at System.Activator.CreateInstance(Type type, Boolean nonPublic)
   at System.Activator.CreateInstance(Type type)
   at AutoMapper.Configuration.MappingExpression`2.<>c__60`1.<AfterMap>g__AfterFunction|60_0(TSource src, TDestination dest, ResolutionContext ctxt) in C:\projects\automapper\src\AutoMapper\Configuration\MappingExpression.cs:line 450
   at lambda_method(Closure , FileServiceRequest , FileSearchRequest , ResolutionContext )
   at lambda_method(Closure , Object , Object , ResolutionContext )
   at AutoMapper.Mapper.AutoMapper.IMapper.Map[TDestination](Object source) in C:\projects\automapper\src\AutoMapper\Mapper.cs:line 207

错误消息是： No parameterless constructor defined for this object.

我确信我做错了什么。请注意，在startup.cs文件中，我尝试过services.AddAutoMapper（typeof（Startup）.Assembly）;同样。它也不起作用。

任何想法，任何人？

谢谢。

Answer 1

仅供参考：我通过切换到使用配置文件而不是直接映射来修复此问题。