如何在c#中通过反射向依赖容器服务注册服务

Question

我有一个接口 IProcessor 和实现该接口的多个处理器：

Processor1 : IProcessor
Processor2 : IProcessor

我想将这些处理器注入到 class 中，例如：IEnumerable<IProcessor> 这样我就可以运行它们一个接一个。

我可以用 Microsoft 依赖项注入容器一个一个地注册这些，但我想通过反射来完成，以便自动注册新添加的处理器。

var processorInterface = typeof(IProcessor);

var processors = Assembly.GetExecutingAssembly().GetTypes()
               .Where(t => processorInterface.IsAssignableFrom(t) && t.IsClass && 
               !t.IsAbstract && t.IsPublic);                  

foreach (var processor in processors)
{
    serviceCollection.AddScoped(processor);

    // Below line does not compile of course
    //serviceCollection.AddScoped<IProcessor, processor>());
}

但这不起作用，我总是得到一个空列表。

Answer 1

AddScoped 已经存在采用服务和实现类型的重载扩展。

/// Adds a scoped service of the type specified in <paramref name="serviceType"/> with an
/// implementation of the type specified in <paramref name="implementationType"/> to the
/// specified <see cref="IServiceCollection"/>.
/// </summary>
/// <param name="services">The <see cref="IServiceCollection"/> to add the service to.</param>
/// <param name="serviceType">The type of the service to register.</param>
/// <param name="implementationType">The implementation type of the service.</param>
/// <returns>A reference to this instance after the operation has completed.</returns>
/// <seealso cref="ServiceLifetime.Scoped"/>
public static IServiceCollection AddScoped(
    this IServiceCollection services,
    Type serviceType,
    [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type implementationType)
{
    ThrowHelper.ThrowIfNull(services);
    ThrowHelper.ThrowIfNull(serviceType);
    ThrowHelper.ThrowIfNull(implementationType);

    return Add(services, serviceType, implementationType, ServiceLifetime.Scoped);
}

Source

将其应用于您的示例时看起来像

//...

foreach (var processor in processors) {
    serviceCollection.AddScoped(processor);

    serviceCollection.AddScoped(processorInterface, processor);
}

//...

Answer 2

我想通过使用属性建议一种不同的方法。

我在这里创建了一个属性，我称之为 InjectableAttribute:

[AttributeUsage(AttributeTargets.Class)]
public class InjectableAttribute: Attribute
{
    public Type ImplementedInterface { get; }
    public DependencyInjectionScope Scope { get; }

    public InjectableAttribute(Type implementedInterface, DependencyInjectionScope scope = DependencyInjectionScope.Singleton)
    {
        ImplementedInterface = implementedInterface;
        Scope = scope;
    }
}

我创建这个枚举也是为了指定依赖的范围：

public enum DependencyInjectionScope
{
    Singleton,
    PerDependency,
    Scoped
}

最后，我创建了这个扩展方法来扫描我的程序集并注入所有具有 InjectableAttribute:

的 classes

namespace Microsoft.Extensions.DependencyInjection
{
    public static class DependencyInjectionExtensions
    {
        public static void RegisterDependencies(this IServiceCollection services, Assembly assembly)
        {
            var types = assembly
                .ExportedTypes
                .Where(x => x.GetCustomAttributes(typeof(InjectableAttribute), true).Length > 0)
                .ToList();

            for (var i = 0; i < types.Count; i++)
            {
                var currentType = types[i];
                var attributes = (InjectableAttribute[])currentType.GetCustomAttributes(typeof(InjectableAttribute),
                    true);
                var attribute = attributes[0];
                var implementedInterface = attribute.ImplementedInterface;
                switch (attribute.Scope)
                {
                    case DependencyInjectionScope.Scoped:
                        services.AddScoped(implementedInterface, currentType);
                        break;
                    case DependencyInjectionScope.PerDependency:
                        services.AddTransient(implementedInterface, currentType);
                        break;
                    case DependencyInjectionScope.Singleton:
                        services.AddSingleton(implementedInterface, currentType);
                        break;
                }
            }
        }
    }
    
}

现在要使用它，这里有一个服务示例 class:

[Injectable(typeof(ICustomerInfoService), DependencyInjectionScope.Scoped)]
public class CustomerInfoService : ICustomerInfoService
{

}

并在我的 ConfigureServices 方法中注册所有内容：

services.RegisterDependencies(typeof(Startup).Assembly);

希望对您有所帮助 :D

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