无法在通用 Class 激活器上找到构造函数

Question

我正在尝试为此 class 创建一个 AutoFixture.ISpecimenBuilder:

public class DiscosObjectRelationship<T> where T : DiscosModelBase
{
    private readonly string _linkAddress;
    private readonly IDiscosClient _client;
    private T? _relatedObject;
    
    public async Task<T?> GetRelatedObject()
    {
        return _relatedObject ?? await LazyLoad();
    }
    internal DiscosObjectRelationship(string linkAddress, IDiscosClient client)
    {
        _linkAddress = linkAddress;
        _client = client;
    }

    private async Task<T?> LazyLoad()
    {
        _relatedObject = (await _client.Get<T>(_linkAddress))?.Attributes;
        return _relatedObject;
    }
}

本质上，我想要它做的就是将 _linkAddress 设置为 Faker.Net 中的随机 URL 并将 _client 设置为 [=18 中的模拟=].我试过这样做：

public class DiscosRelationshipSpecimenBuilder: ISpecimenBuilder
{
    public object Create(object request, ISpecimenContext context)
    {
        if (request is Type {IsGenericType: true} type && type.GetGenericTypeDefinition() == typeof(DiscosObjectRelationship<>))
        {
            return Activator.CreateInstance(type, Faker.Internet.Url(), Substitute.For<IDiscosClient>()) ?? new NoSpecimen();
        }

        return new NoSpecimen();
    }
}

但是，它会抛出一个错误，提示无法找到该类型的构造函数。这让我感到困惑（据我所知）我提供了正确的参数（分别为 string 和 IDiscosClient）。

完整的例外是：

System.MissingMethodException: Constructor on type 'DISCOSweb_Sdk.Models.Relationships.DiscosObjectRelationship`1[[DISCOSweb_Sdk.Models.ResponseModels.Reentries.Reentry, DISCOSweb-Sdk, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]' not found.
    at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture)
    at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
    at System.Activator.CreateInstance(Type type, Object[] args)
    at DISCOSweb_Sdk.Tests.Fixtures.AutoFixture.DiscosRelationshipSpecimenBuilder.Create(Object request, ISpecimenContext context) in /home/james/repos/DISOSweb-sdk/src/DISCOSweb-Sdk/DISCOSweb-Sdk.Tests/Fixtures/AutoFixture/DiscosRelationshipSpecimenBuilder.cs:line 17
    at AutoFixture.Kernel.CompositeSpecimenBuilder.Create(Object request, ISpecimenContext context)
    at AutoFixture.CustomizationNode.Create(Object request, ISpecimenContext context)
    at AutoFixture.Kernel.CompositeSpecimenBuilder.Create(Object request, ISpecimenContext context)
    at AutoFixture.Kernel.TerminatingWithPathSpecimenBuilder.Create(Object request, ISpecimenContext context)

我做错了什么？

Answer 1

Activator.CreateInstance() 默认只查找 public 构造函数。如果要查找构造函数的其他范围，则需要使用 BindingFlags.

的重载

需要的标志是：

const BindingFlags flags = BindingFlags.NonPublic | BindingFlags.Instance;

您可能还想使用 InvariantCulture，因此整个调用类似于：

return Activator.CreateInstance(type, flags, null, new object[] {myArgs}, CultureInfo.InvariantCulture;)

无法在通用 Class 激活器上找到构造函数

Can't Find Constructor on Generic Class Activator

c#

generics

autofixture

nsubstitute