自动映射器ConstructUsing方法不起作用

Question

我在使用ConstructUsing方法时遇到麻烦。即使解决了上下文，“缩略图”字段也不会更改。有任何建议吗？

var command = Mapper.Map<CreateDeviceApp.Command>(
    model, 
    opt => { opt.Items["Thumbnail"] = uploadImageResponse.Uri; });

CreateMap<CreateDeviceAppViewModel, CreateDeviceApp.Command>()
    .ConstructUsing((src, ctxt) => 
        new CreateDeviceApp.Command() 
            { Thumbnail = ctxt.Options.Items["Thumbnail"].ToString() });