c# - 尝试将类型注册到 IoC 容器时，HttpContext.Current 为空

Question

我正在尝试在我的 ASP.NET MVC 5 应用程序中设置 IoC 容器，以便我可以在我的应用程序中的任何位置访问这些对象。

我选择使用Unity.Mvc作业的容器。

在我的类型注册步骤中，我尝试运行以下代码

var httpContext = new HttpContextWrapper(HttpContext.Current);
container.RegisterInstance<HttpContextBase>(httpContext);

var sessionWrapper = new HttpSessionStateWrapper(HttpContext.Current.Session);
container.RegisterInstance<HttpSessionStateBase>(sessionWrapper);

var httpServerUtility = new HttpServerUtilityWrapper(HttpContext.Current.Server);
container.RegisterInstance<HttpServerUtilityBase>(httpServerUtility);

但是，HttpContext.Current.Session 行抛出空异常，因为 HttpContext.Current 对象为 null。

如何正确地将非空 HttpContextWrapper 实例注入(inject)到我的 IoC 容器中？

Answer 1

How can I correctly inject a non-null HttpContextWrapper instance into my IoC container?

这些行涵盖了所有 3 种情况(HttpContext、HttpContext.Session 和 HttpContext.Server):

var httpContext = new HttpContextWrapper(HttpContext.Current);
container.RegisterInstance<HttpContextBase>(httpContext);

由于在应用程序启动期间没有 session ，因此您无法在 MVC 5 Application Lifecycle 中尽早访问它们.

将 httpContext 注入(inject)组件后，您可以在应用程序的运行时 部分访问 session 状态。

public class SomeService : ISomeService
{
    private readonly HttpContextBase httpContext;

    public SomeService(HttpContextBase httpContext)
    {
        if (httpContext == null)
            throw new ArgumentNullException(nameof(httpContext));
        this.httpContext = httpContext;
        // Session state is still null here...
    }

    public void DoSomething()
    {
        // At runtime session state is available.
        var session = httpContext.Session;
    }
}

NOTE: It is generally not a good practice to make your services depend directly on session state. Instead, you should have the controller pass session state values through method parameters (i.e. DoSomething(sessionValue)), or alternatively implement a SessionStateAccessor wrapper around HttpContextBase that can be injected into your services, similar to how it is done in ASP.NET Core.