c# - ASP.NET 5 MVC 6 DI : ServiceProvider not resolving type

Question

在下面的代码中，serviceProvider.GetService<DocumentDbConnection>()正在解析为 null :

public void ConfigureService(IServiceCollection services)
{
    var serviceProvider = services.BuildServiceProvider();

    services.AddSingleton<DocumentDbConnection>(
        x => new DocumentDbConnection(uri, authKey));

    // service is null?
    var connection = serviceProvider.GetService<DocumentDbConnection>();

    services.AddTransient<IStopRepository, StopRepository>(
        x => new StopRepository(connection, databaseId, collectionId));
}

为什么会这样？该类型在 GetService 之前注册被调用所以它不应该解析为单例吗？

Answer 1

您在注册 DocumentDbConnection 之前构建服务提供者。您应该首先注册您需要的服务。然后 BuildServiceProvider 将使用之前注册的服务构建一个服务提供者:

services.AddSingleton<DocumentDbConnection>(x => new DocumentDbConnection(uri, authKey));
var serviceProvider = services.BuildServiceProvider();

// code using serviceProvider