dependency-injection - 统一: Implicit ResolvedParameter for unnamed registrations

Question

UserService构造函数有两个参数，一个 IUnitOfWork和 IUserRepository :

public UserService(IUnitOfWork unitofWork, IUserRepository userRepository) 
{ ... }

我正在使用 named registrations区分 IUnitOfWork 的多个实例，所以在注册 UserService 时对于 Unity 容器，我需要使用 InjectionConstructor 显式指定参数:

container.RegisterType<IUserService, UserService>(
    new InjectionConstructor(
        new ResolvedParameter<IUnitOfWork>("someContext"),
        new ResolvedParameter<IUserRepository>()
    )
);

new ResolvedParameter<IUserRepository>() 有可能吗？被省略？我希望 Unity 隐式推断此参数，因为不需要命名注册。 代码如下所示:

container.RegisterType<IUserService, UserService>(
    new InjectionConstructor(
        new ResolvedParameter<IUnitOfWork>("someContext")
    )
);

在我不需要使用 InjectionConstructor 的任何情况下都会这样做。 .

Answer 1

基于 InjectionConstructor ，我想出了这个RequiredInjectionConstructor。它允许您指定任何一组参数，并且它将尝试找到一个构造函数，该构造函数需要(至少)具有传递的注入(inject)参数集。如果有多个构造函数满足这个条件，它会选择参数数量最少的构造函数。其余的构造函数参数假定为未命名的已解析参数。

我还没有对其进行一整套单元测试，所以如果您遇到任何问题，请告诉我。

/// <summary>
/// A class that holds the collection of minimum required
/// parameters for a constructor, so that the container can
/// be configured to call this constructor.
/// </summary>
public class RequiredInjectionConstructor : InjectionMember
{
    private readonly List<InjectionParameterValue> _requiredParameterValues;

    /// <summary>
    /// Create a new instance of <see cref="RequiredInjectionConstructor"/> that looks
    /// for a constructor with a minimum of the given required set of parameters.
    /// </summary>
    /// <param name="requiredParameterValues">The values for the parameters, that will
    /// be converted to <see cref="InjectionParameterValue"/> objects.</param>
    public RequiredInjectionConstructor(params object[] requiredParameterValues)
    {
        _requiredParameterValues = InjectionParameterValue.ToParameters(requiredParameterValues).ToList();
    }

    /// <summary>
    /// Add policies to the <paramref name="policies"/> to configure the
    /// container to call this constructor with the required parameter values.
    /// </summary>
    /// <param name="serviceType">Interface registered, ignored in this implementation.</param>
    /// <param name="implementationType">Type to register.</param>
    /// <param name="name">Name used to resolve the type object.</param>
    /// <param name="policies">Policy list to add policies to.</param>
    public override void AddPolicies(Type serviceType, Type implementationType, string name, IPolicyList policies)
    {
        ConstructorInfo ctor = FindConstructor(implementationType, _requiredParameterValues);
        IEnumerable<InjectionParameterValue> selectedConstructorParameterValues = GetSelectedConstructorParameterValues(ctor, _requiredParameterValues);

        policies.Set<IConstructorSelectorPolicy>(
            new SpecifiedConstructorSelectorPolicy(ctor, selectedConstructorParameterValues.ToArray()),
            new NamedTypeBuildKey(implementationType, name));
    }

    private static ConstructorInfo FindConstructor(Type typeToCreate, IEnumerable<InjectionParameterValue> requiredInjectionParameters)
    {
        var typeToCreateReflector = new ReflectionHelper(typeToCreate);

        var matchedConstructors = typeToCreateReflector.InstanceConstructors.
            Where(ctor =>
            {
                var constructorParameterTypes = ctor.GetParameters().Select(info => info.ParameterType);
                return requiredInjectionParameters.All(required => constructorParameterTypes.Any(required.MatchesType));
            });

        if (matchedConstructors.Any())
        {
            // Prefer the constructor that has the least number of arguments.
            // Other preference models could be implemented here. 
            return matchedConstructors.OrderBy(ctor => 
                ctor.GetParameters().Count()).
                FirstOrDefault();
        }

        string signature = string.Join(", ", requiredInjectionParameters.Select(required => required.ParameterTypeName).ToArray());

        throw new InvalidOperationException(
            string.Format("Unable to find a constructor with the minimum required parameters.  Type: {0}, RequiredParameters: {1}",
                typeToCreate.FullName,
                signature));
    }

    private static IEnumerable<InjectionParameterValue> GetSelectedConstructorParameterValues(ConstructorInfo ctor, IEnumerable<InjectionParameterValue> requiredInjectionParameters)
    {
        var injectionParameterValues = new List<InjectionParameterValue>();

        foreach (var parameter in ctor.GetParameters())
        {
            var existingInjectionParameter = requiredInjectionParameters.FirstOrDefault(required => required.MatchesType(parameter.ParameterType));
            injectionParameterValues.Add(existingInjectionParameter ?? new ResolvedParameter(parameter.ParameterType));
        }

        return injectionParameterValues;
    }
}