从 ViewComponent returns 访问 HttpContext.Items NULL

Question

我们正在关注此官方 ASP.NET 文档：Managing Application State. In our one we controller we're setting a value for HttpContext.Items[...] and are trying to access that value from a ViewComponent 从相应的视图调用。但是我们在 ViewComponent.

中将 HttpContext.Items[...] 设为 null

控制器：

HttpContext.Items["TestVal"]= "some value";

查看：

@await Component.InvokeAsync("myVC")

ViewComponent:

public class myVCViewComponent : ViewComponent
{
    public async Task<IViewComponentResult> InvokeAsync()
    {
        String myVal= Http.Items["TestVal"].ToString(); //issue: Http.Items["TestVal"] is null at this line
        return View(items);
    }
}

更新:

在上面的控制器部分，将 Http.Items 更改为 HttpContext.Items 行中的 HttpContext.Items["TestVal"]= "some value";

Answer 1

最终更新：

我已经像您的示例一样测试了简单的案例，并且效果很好（在 MVC Core v1.1.0 上）。

因此，很难说为什么它在您的特定情况下不起作用。

然而，在我们在评论中进行讨论后，您找到了问题的根源：

I realised the issue is not related to ViewComponent; it's rather related to scope of HttpContext

原回答：

在文档中您可以阅读：

Its contents are discarded after each request. It is best used as a means of communicating between components or middleware that operate at different points in time during a request

和 Working with HttpContext.Items 部分：

This collection is available from the start of an HttpRequest and is discarded at the end of each request.

并在 View Components documentation 中：

Are overloaded on the signature rather than any details of the current HTTP request

Answer 2

HttpContext.Current 在 ASP.NET Core 中是不可能的。从单独的 class 库访问当前 HTTP 上下文是 ASP.NET Core 试图避免的那种混乱架构。

但是可以使用 ASP.NET 核心依赖注入系统中的 IHttpContextAccessor 获取上下文：

public class SomeClass
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public SomeClass(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }
}

当 HttpContextAccessor 被注入时，你可以做类似的事情：var context = _httpContextAccessor.HttpContext;.

从 ViewComponent returns 访问 HttpContext.Items NULL

Accessing HttpContext.Items from ViewComponent returns NULL

c#

asp.net-core

asp.net-core-viewcomponent