Startup.cs ConfigureServices 方法中的 ASP.NET Core 访问服务

Question

我需要在 Startup.cs 的 ConfigureServices 方法中访问一个服务，我这样做：

services.AddScoped<ICustomService, CustomService>();

var sp = services.BuildServiceProvider();

var service = sp.GetService<ICustomService>(); // this is null

但是上面的var service 始终为空。

我做错了什么？

Answer 1

我遇到了这样的问题 - 我有一个我想使用的单例“设置”服务。我通过实际创建一个然后通过允许您指定“提供者”的重载向 DI 注册该确切实例来解决它，而不仅仅是注册类，并添加一个很好的大注释来解释这一点：

var settingsService = new SettingsService(_hostingEnvironment);

//Add a concrete settings service which is then registered as the de facto settings service for all time.
//we need to do this as we want to use the settings in this method, and there isn't a satisfactory method to 
//pull it back out of the IServiceCollection here (we could build a provider, but then that's not the same provider
//as would be build later... at least this way I have the exact class I'll be using.
services.AddSingleton<ISettingsService, SettingsService>((p) => settingsService);

..
..
..
var thing = settingsService.SomeSettingIWant();

如果你想要的不是单例而是暂时的，那么我想你可以在那里为它创建一个具体的类？我知道这可能感觉有点像作弊，但它会工作得很好......