c# - 值不能为空。参数名称 : type

Question

在阅读并尝试了 stackExchange 上的答案后，我仍然在以下代码中得到一个空值:

    typeOfIMydServiceBase.Assembly
            .GetExportedTypes()
            .Where(exportedType => typeOfMydServiceBase != exportedType && typeOfMydServiceBase.IsAssignableFrom(exportedType))
            .Select(mydServiceType => new
            {
                serviceType = mydServiceType,
                interfaceType = mydServiceType.GetInterfaces().First(@interface => @interface != typeOfIMydServiceBase && typeOfIMydServiceBase.IsAssignableFrom(@interface))
            })
            .ToList()
            .ForEach(registrationInfo => container.Register(registrationInfo.interfaceType, () =>
            {
                var method = serviceActivatorType
                    .GetMethod("GetService", serviceActivatorParams)
                    .MakeGenericMethod(new[] { registrationInfo.interfaceType });
                var result = method.Invoke(new ServiceActivator(), null);

                return result;
            }, WebApiRequestLifestyleWithDisposal));

结果一直返回为 null，当我使用 Object[] {null} 或 Object[]{} 或 Object[]{null,null,etc} 时，我得到参数不匹配。

注意:这是我收到的上述代码的错误消息:

Line 156: .MakeGenericMethod(new[] { registrationInfo.interfaceType });

Line 157:

Line 158: var result = method.Invoke(new ServiceActivator(), null);

Line 159:

Line 160: return result;

有谁知道这里发生了什么以及我该如何解决？？？？

{
public class ServiceActivator
{
    public ServiceActivator();
    public ServiceActivator(IServiceConfigurationReader configurationReader);

    public T GetService<T>();
    public T GetService<T>(string key);
}

与上述内容相关的还有所用服务的注册。见下文:

//Scan and register business servics
        var typeOfIMydServiceBase = typeof(IMydServiceBase);
        var typeOfMydServiceBase = typeof(MydServiceBase);
        var serviceActivatorType = typeof(ServiceActivator);
        var serviceActivatorParams = new Type[0];

更新:在 serviceActivator 参数中使用 typeof(string) 可以工作，但是我得到了一个未处理的异常。这是新错误:

Line 166:                    p.ServiceContainer = container;
Line 167:                });
Line 168:
Line 169:                container.RegisterWebApiControllers(config);
Line 170:            }

属于以下代码:

var typeOfIMydServiceBase = typeof(IMydServiceBase);
        var typeOfMydServiceBase = typeof(MydServiceBase);
        var serviceActivatorType = typeof(ServiceActivator);
        var serviceActivatorParams = new Type[] { typeof(string) };
        
        typeOfIMydServiceBase.Assembly
            .GetExportedTypes()
            .Where(exportedType => typeOfMydServiceBase != exportedType && typeOfMydServiceBase.IsAssignableFrom(exportedType))
            .Select(mydServiceType => new
            {
                serviceType = mydServiceType,
                interfaceType = mydServiceType.GetInterfaces().First(@interface => @interface != typeOfIMydServiceBase && typeOfIMydServiceBase.IsAssignableFrom(@interface))
            })
            .ToList()
            .ForEach(registrationInfo => container.Register(registrationInfo.interfaceType, () =>
            {
                
                var method = serviceActivatorType
                    .GetMethod("GetService", serviceActivatorParams)
                    .MakeGenericMethod(new[] { registrationInfo.interfaceType });
           
                var result = method.Invoke(new ServiceActivator(), null);

                return result;
            }, WebApiRequestLifestyleWithDisposal));
        {

            container.RegisterInitializer<IMydServiceBase>(p =>
            {
                p.ServiceContainer = container;
            });

            container.RegisterWebApiControllers(config);
        }
    }

Answer 1

var method = serviceActivatorType
.GetMethod("GetService", serviceActivatorParams)

返回 public T GetService<T>(); 与 var serviceActivatorParams = new Type[0]; (来自问题中的评论讨论)

但是这一行:

var result = method.Invoke(new ServiceActivator(), null);

将要调用这个方法:

public T GetService<T>(string key);

通过 null作为 string key 的值.

public T GetService<T>(); 没有要传递的参数，这就是它抛出异常的原因。

要解决您的问题，请尝试:

var serviceActivatorParams = new Type[] { typeof(string) };

或者在没有 null 的情况下调用您的方法参数:

var result = method.Invoke(new ServiceActivator());