[ASP.NET Core]ASP.NET Core应用程序开发中如何使用@Html.Action？

问题描述

在ASP.NET MVC的应用程序开发中，Razor视图页面可以使用@Html.Action扩展方法可渲染页面，但在ASP.NET Core的Razor视图页面中没有了@Html.Action这个扩展方法了，而是ViewComponents组件。那么，在ASP.NET Core应用程序开发中是否不可用@Html.Action扩展了呢？

方案一

在ASP.NET Core中微软官方的确没有实现@Html.Action这个扩展方法了，取而代之的是ViewComponents组件，而且ViewComponents组件的功能也非常强大，但对Ajax的支持不是太好。
如果你仍然想在ASP.NET Core中使用@Html.Action，可以自己实现@Html.Action扩展方法，如：

using System;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Extensions;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Controllers;
using Microsoft.AspNetCore.Mvc.Internal;
using Microsoft.AspNetCore.Mvc.Infrastructure;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Routing;

namespace Microsoft.AspNetCore.Mvc.Rendering    {

    public static class HtmlHelperViewExtensions
    {

        public static IHtmlContent RenderAction(this IHtmlHelper helper, string action, object parameters = null)
        {
            var controller =  (string)helper.ViewContext.RouteData.Values["controller"];

            return RenderAction(helper, action, controller, parameters);
        }

        public static IHtmlContent RenderAction(this IHtmlHelper helper, string action, string controller, object parameters = null)
        {
            var area = (string)helper.ViewContext.RouteData.Values["area"];

            return RenderAction(helper, action, controller, area, parameters);
        }

        public static IHtmlContent RenderAction(this IHtmlHelper helper, string action, string controller, string area, object parameters = null)
        {
            if (action == null)
                throw new ArgumentNullException("action");

            if (controller == null)
                throw new ArgumentNullException("controller");

            if (area == null)
                throw new ArgumentNullException("area");

            var task = RenderActionAsync(helper, action, controller, area, parameters);

            return task.Result;
        }

        private static async Task<IHtmlContent> RenderActionAsync(this IHtmlHelper helper, string action, string controller, string area, object parameters = null)
        {
            var currentHttpContext = helper.ViewContext?.HttpContext;
            var httpContextFactory = GetServiceOrFail<IHttpContextFactory>(currentHttpContext);
            var actionInvokerFactory = GetServiceOrFail<IActionInvokerFactory>(currentHttpContext);
            var actionSelector = GetServiceOrFail<IActionSelectorDecisionTreeProvider>(currentHttpContext);

            var routeData = new RouteData();
            var routeParams = new RouteValueDictionary(parameters ?? new { });
            var routeValues = new RouteValueDictionary(new { area = area, controller = controller, action = action });
            var newHttpContext = httpContextFactory.Create(currentHttpContext.Features);

            newHttpContext.Response.Body = new MemoryStream();

            foreach (var router in helper.ViewContext.RouteData.Routers)
                routeData.PushState(router, null, null);

            routeData.PushState(null, routeValues, null);
            routeData.PushState(null, routeParams, null);

            var actionDescriptor = actionSelector.DecisionTree.Select(routeValues).First();
            var actionContext = new ActionContext(newHttpContext, routeData, actionDescriptor);

            var invoker = actionInvokerFactory.CreateInvoker(actionContext);
            string content = null;

            await invoker.InvokeAsync().ContinueWith(task => {
                if (task.IsFaulted)
                {
                    content = task.Exception.Message;
                }
                else if (task.IsCompleted)
                {
                    newHttpContext.Response.Body.Position = 0;
                    using (var reader = new StreamReader(newHttpContext.Response.Body))
                        content = reader.ReadToEnd();
                }
            });

            return new HtmlString(content);
        }

        private static TService GetServiceOrFail<TService>(HttpContext httpContext)
        {
            if (httpContext == null)
                throw new ArgumentNullException(nameof(httpContext));

            var service = httpContext.RequestServices.GetService(typeof(TService));

            if (service == null)
                throw new InvalidOperationException($"Could not locate service: {nameof(TService)}");

            return (TService)service;
        }
    }
}

在Razor视图页面中的使用示例如：

@Html.RenderAction("action", "controller", "area", new { id = 1})
@Html.RenderAction("action", "controller", new { id = 1})
@Html.RenderAction("action", new { id = 1})

方案二

其中IHtmlHelper的@Html.Action另一个静态扩展方法实现代码，如下：

using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Infrastructure;
using Microsoft.AspNetCore.Routing;
using Microsoft.Extensions.DependencyInjection;
using System;
using System.IO;
using System.Threading.Tasks;

namespace Microsoft.AspNetCore.Mvc.Rendering
{
    public static class HtmlHelperViewExtensions
    {
        public static IHtmlContent Action(this IHtmlHelper helper, string action, object parameters = null)
        {
            var controller = (string)helper.ViewContext.RouteData.Values["controller"];

            return Action(helper, action, controller, parameters);
        }

        public static IHtmlContent Action(this IHtmlHelper helper, string action, string controller, object parameters = null)
        {
            var area = (string)helper.ViewContext.RouteData.Values["area"];

            return Action(helper, action, controller, area, parameters);
        }

        public static IHtmlContent Action(this IHtmlHelper helper, string action, string controller, string area, object parameters = null)
        {
            if (action == null)
                throw new ArgumentNullException("action");

            if (controller == null)
                throw new ArgumentNullException("controller");


            var task = RenderActionAsync(helper, action, controller, area, parameters);

            return task.Result;
        }

        private static async Task<IHtmlContent> RenderActionAsync(this IHtmlHelper helper, string action, string controller, string area, object parameters = null)
        {
            var serviceProvider = helper.ViewContext.HttpContext.RequestServices;
            var actionContextAccessor = helper.ViewContext.HttpContext.RequestServices.GetRequiredService<IActionContextAccessor>();
            var httpContextAccessor = helper.ViewContext.HttpContext.RequestServices.GetRequiredService<IHttpContextAccessor>();
            var actionSelector = serviceProvider.GetRequiredService<IActionSelector>();

            var routeData = new RouteData();
            foreach (var router in helper.ViewContext.RouteData.Routers)
            {
                routeData.PushState(router, null, null);
            }
            routeData.PushState(null, new RouteValueDictionary(new { controller = controller, action = action, area = area }), null);
            routeData.PushState(null, new RouteValueDictionary(parameters ?? new { }), null);

            RouteContext routeContext = new RouteContext(helper.ViewContext.HttpContext) { RouteData = routeData };
            var candidates = actionSelector.SelectCandidates(routeContext);
            var actionDescriptor = actionSelector.SelectBestCandidate(routeContext, candidates);

            var originalActionContext = actionContextAccessor.ActionContext;
            var originalhttpContext = httpContextAccessor.HttpContext;
            try
            {
                var newHttpContext = serviceProvider.GetRequiredService<IHttpContextFactory>().Create(helper.ViewContext.HttpContext.Features);
                if (newHttpContext.Items.ContainsKey(typeof(IUrlHelper)))
                {
                    newHttpContext.Items.Remove(typeof(IUrlHelper));
                }
                newHttpContext.Response.Body = new MemoryStream();
                var actionContext = new ActionContext(newHttpContext, routeData, actionDescriptor);
                actionContextAccessor.ActionContext = actionContext;
                var invoker = serviceProvider.GetRequiredService<IActionInvokerFactory>().CreateInvoker(actionContext);
                await invoker.InvokeAsync();
                newHttpContext.Response.Body.Position = 0;
                using (var reader = new StreamReader(newHttpContext.Response.Body))
                {
                    return new HtmlString(reader.ReadToEnd());
                }
            }
            catch (Exception ex)
            {
                return new HtmlString(ex.Message);
            }
            finally
            {
                actionContextAccessor.ActionContext = originalActionContext;
                httpContextAccessor.HttpContext = originalhttpContext;
                if (helper.ViewContext.HttpContext.Items.ContainsKey(typeof(IUrlHelper)))
                {
                    helper.ViewContext.HttpContext.Items.Remove(typeof(IUrlHelper));
                }
            }
        }
    }
}