Question

如何在中间件中获取UrlHelper。我尝试如下，但actionContextAccessor.ActionContext返回null。

public void ConfigureServices(IServiceCollection services)
{
    services.AddSession();

    services
        .AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
        .AddCookie();

    services.AddMvc();
    services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseSession();

    if (env.IsDevelopment())
    {
        app.UseBrowserLink();
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
    }

    app.UseStaticFiles();
    app.UseAuthentication();
    app.Use(async (context, next) =>
    {
        var urlHelperFactory = context.RequestServices.GetService<IUrlHelperFactory>();
        var actionContextAccessor = context.RequestServices.GetService<IActionContextAccessor>();

        var urlHelper = urlHelperFactory.GetUrlHelper(actionContextAccessor.ActionContext);
        await next();
        // Do logging or other work that doesn't write to the Response.
    });

    app.UseMvc(routes =>
    {
        routes.MapRoute(
            name: "default",
            template: "{controller=Home}/{action=Index}/{id?}");
    });
}

Answer 1

您的应用中有2个管道。您正在连接的ASP.NET核心管道。以及由UseMvc设置的ASP.NET MVC管道。 ActionContext是一个MVC概念，这就是它在ASP.NET核心管道中不可用的原因。要挂钩MVC管道，您可以使用过滤器：https://docs.microsoft.com/en-us/aspnet/core/mvc/controllers/filters

编辑：修正了文章的链接

Answer 2

您可以尝试将其添加到ConfigureServices(IServiceCollection services)上的服务容器中。你可以这样做：

 public IServiceProvider ConfigureServices(IServiceCollection services) {
    //Service injection and setup
    services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();
                services.AddScoped<IUrlHelper>(factory =>
                {
                    var actionContext = factory.GetService<IActionContextAccessor>()
                                               .ActionContext;
                    return new UrlHelper(actionContext);
                });

    //....

   // Build the intermediate service provider then return it
    return services.BuildServiceProvider();
}

然后，您可以修改Configure()方法以接收IServiceProvider，然后您可以通过执行以下操作获取UrlHelper的实例。

public void Configure(IApplicationBuilder app, IServiceProvider serviceProvider) {

    //Code removed for brevity

    var urlHelper = serviceProvider.GetService<IUrlHelper>(); <-- helper instance

    app.UseMvc();
}

注意：将其放在services.Mvc()

之后

在中间件asp.net mvc core 2.0中获取UrlHelper

2 个答案: