How to access current absolute Uri from any ASP .Net Core class?

问题

I am trying to figure out how to access the current absolute Uri -- i.e. the absolute url of the view that is currently being rendered -- from a user class in .Net Core 1.1

I found this link but it seems to be outdated and throws error after error: Getting absolute URLs using ASP.NET Core MVC 6

In my Startup.cs I have under ConfigureServices:

services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();

In my Startup.cs I have under Configure:

IHttpContextAccessor httpContextAccessor = app.ApplicationServices.GetRequiredService<IHttpContextAccessor>();
Extensions.Context.Configure(httpContextAccessor);

I have the following class:

using Microsoft.AspNetCore.Http;
using System;

namespace Framework.Extensions
{
    public static class Context
    {
        private static IHttpContextAccessor HttpContextAccessor;
        public static void Configure(IHttpContextAccessor httpContextAccessor)
        {
            HttpContextAccessor = httpContextAccessor;
        }

        private static HttpContext GetCurrentContext()
        {
            return HttpContextAccessor.HttpContext;
        }
        public static HttpContext Current = GetCurrentContext();

        private static Uri GetAbsoluteUri()
        {
            UriBuilder uriBuilder = new UriBuilder();
            uriBuilder.Scheme = GetCurrentContext().Request.Scheme;
            uriBuilder.Host = GetCurrentContext().Request.Host.ToString();
            uriBuilder.Path = GetCurrentContext().Request.Path.ToString();
            uriBuilder.Query = GetCurrentContext().Request.QueryString.ToString();
            return uriBuilder.Uri;
        }
        public static Uri AbsoluteUri = GetAbsoluteUri();
        public static string Url = GetAbsoluteUri().ToString();
        public static string AbsolutePath = GetAbsoluteUri().AbsolutePath;
    }
}

I get the following exception:

System.TypeInitializationException was unhandled by user code
HResult=-2146233036 Message=The type initializer for 'Framework.Extensions.Context' threw an exception.
TypeName=Framework.Extensions.Context InnerException: HResult=-2147467261 Message=Object reference not set to an instance of an object. Source=www StackTrace: at Framework.Extensions.Context.GetCurrentContext() in E:\Websites\Stage\www\Extensions\Context.cs:line 16 at Framework.Extensions.Context..cctor() in E:\Websites\Stage\www\Extensions\Context.cs:line 18 InnerException:

回答1:

You want the IHttpContextAccessor "configured or injected" in your Startup so later on when you use the helper during the context of a request you can use it to access the current HttpContext object.

You cannot store the context on a static field as that context only makes sense while serving a specific request. Typically you will leave the accessor in a static field and use it every time your helper is called.

Even worse you are using static fields with initializers, which are executed the first time the class is used. That means they are executed right before you call the Configure method, so there will be no IHttpContextAccessor yet configured and you will get those null references.

This would be a simple thing of writing what you want:

public static class Context
{
    private static IHttpContextAccessor HttpContextAccessor;
    public static void Configure(IHttpContextAccessor httpContextAccessor)
    {
        HttpContextAccessor = httpContextAccessor;
    }

    private static Uri GetAbsoluteUri()
    {
        var request = HttpContextAccessor.HttpContext.Request;
        UriBuilder uriBuilder = new UriBuilder();
        uriBuilder.Scheme = request.Scheme;
        uriBuilder.Host = request.Host.Host;
        uriBuilder.Path = request.Path.ToString();
        uriBuilder.Query = request.QueryString.ToString();
        return uriBuilder.Uri;
    }

    // Similar methods for Url/AbsolutePath which internally call GetAbsoluteUri
    public static string GetAbsoluteUrl() { }
    public static string GetAbsolutePath() { }
}

One more thing to bear in mind:

In the original question, the helper was created as a static class because they were created as extension methods. If you are not using extension methods you are not forced to use a static class.

回答2:

You may use the GetDisplayUrl extension method.

var url = httpContextAccessor.HttpContext?.Request?.GetDisplayUrl();

Assuming httpContextAccessor is an object of IHttpContextAccessor which was injected via DI.

This extension method is defined in Microsoft.AspNetCore.Http.Extensions namespace. So you need to have a using statement to include it in your file.

using Microsoft.AspNetCore.Http.Extensions;

来源：https://stackoverflow.com/questions/42547653/how-to-access-current-absolute-uri-from-any-asp-net-core-class

标签

asp.net-core-mvc