如何确定服务是否已添加到 IServiceCollection

Question

我正在创建帮助类以通过IServiceCollection 为库简化接口的配置和注入。库构造函数包含许多可能较早注入的依赖项。如果它们尚未插入IServiceCollection，则帮助程序类应添加它们。如何检测接口是否已经注入？

public static void AddClassLibrary(this IServiceCollection services
    , IConfiguration configuration)
{
     //Constructor for ClassLibrary requires LibraryConfig and IClass2 to be in place
     //TODO: check IServiceCollection to see if IClass2 is already in the collection. 
     //if not, add call helper class to add IClass2 to collection. 
     //How do I check to see if IClass2 is already in the collection?
     services.ConfigurePOCO<LibraryConfig>(configuration.GetSection("ConfigSection"));
     services.AddScoped<IClass1, ClassLibrary>();
}

Answer 1

Microsoft 已包含扩展方法以防止添加已存在的服务。例如：

// services.Count == 117
services.TryAddScoped<IClass1, ClassLibrary>();
// services.Count == 118
services.TryAddScoped<IClass1, ClassLibrary>();
// services.Count == 118

要使用它们，您需要添加以下 using 指令：

using Microsoft.Extensions.DependencyInjection.Extensions;

如果内置方法不能满足您的需求，您可以通过检查服务的ServiceType来检查服务是否存在。

if (!services.Any(x => x.ServiceType == typeof(IClass1)))
{
    // Service doesn't exist, do something
}