ASP.NET MVC"Donut caching"和TempData

是否有任何解决方案来访问HttpResponseBase.WriteSubstitution()方法中的TempData属性

这不起作用:

<%= Response.WriteSubstitution(x => Html.Encode(TempData["message"].ToString())) %>

但这有效:

<%= Response.WriteSubstitution(x => DateTime.Now.ToString()) %>

问题出在一次缓存页面的请求处理中.根据http://msdn.microsoft.com/en-us/library/system.web.httpresponse.writesubstitution.aspx:

在对页面的第一个请求中,WriteSubstitution调用HttpResponseSubstitutionCallback委托来生成输出.然后,它为响应添加一个替换缓冲区,该代码保留委托以便在将来的请求上调用.最后,它将客户端可缓存性从公共服务器降级到仅服务器,确保将来对页面的请求通过不在客户端上缓存来重新调用委托.

换句话说,委托无权访问Session属性(SessionStateTempDataProvider在会话中存储TempData),因为没有"正常"的请求生命周期.据我所知,它是在HttpApplication.ResolveRequestCache/HttpApplication.PostResolveRequestCache事件处理的,但当前状态是在HttpApplication.AcquireRequestState事件中获取的(http://msdn.microsoft.com/en-us/library/ms178473.aspx)

也许我需要某种"高级自定义TempDataProvider":)任何想法？

我找到了解决方案:

主要思想是在缓存中保存TempData的副本,并在每个请求中进行检索.该解决方案是自定义TempDataProvider和简单http模块的组合.另外还有几个助手和静态类.

这是代码:

CustomTempDataProvider:

using System;
using System.Collections.Generic;
using System.Web;
using System.Web.Caching;
using System.Web.Mvc;

public class CustomTempDataProvider : SessionStateTempDataProvider, IHttpModule
{
    public void Init(HttpApplication application)
    {
        application.BeginRequest += new EventHandler(application_BeginRequest);
    }

    void application_BeginRequest(object sender, EventArgs e)
    {
        var httpContext = HttpContext.Current;
        var tempData = httpContext.Cache[TempDataKey] ?? new Dictionary(StringComparer.OrdinalIgnoreCase);
        httpContext.Items.Add("TempData", tempData);
        httpContext.Cache.Remove(TempDataKey);
    }

    public override void SaveTempData(ControllerContext controllerContext,
        IDictionary values)
    {
        HttpContext.Current.Cache.Insert(TempDataKey, values, null, DateTime.Now.AddMinutes(5), Cache.NoSlidingExpiration, CacheItemPriority.NotRemovable, null);
        base.SaveTempData(controllerContext, values);
    }

    public static string TempDataKey
    {
        get
        {
            string sessionID = "0";
            var httpContext = HttpContext.Current;
            if(httpContext.Session != null)
            {
                sessionID = httpContext.Session.SessionID;
            }
            else if (httpContext.Request.Cookies["ASP.NET_SessionId"] != null)
            {
                sessionID = httpContext.Request.Cookies["ASP.NET_SessionId"].Value;
            }
            return "TempData-For-Session-" + sessionID;
        }
    }

    public void Dispose()
    {
    }
}

在web.config中注册它:

CustomControllerFactory:

using System.Web.Routing;
using System.Web.Mvc;

public class CustomControllerFactory : DefaultControllerFactory
{
    public override IController CreateController(
        RequestContext requestContext, string controllerName)
    {
        var controller = (Controller)base.CreateController(requestContext, controllerName);
        controller.TempDataProvider = new CustomTempDataProvider();
        return controller;
    }
}

在Global.asax中注册它:

protected void Application_Start()
{
    RegisterRoutes(RouteTable.Routes);

    ControllerBuilder.Current.SetControllerFactory(typeof(CustomControllerFactory));
}

用于访问TempData的静态类:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

public static class CustomTempData
{
    public static object Get(string key)
    {
        var tempData = HttpContext.Current.Items["TempData"] as IDictionary;
        var item = tempData.FirstOrDefault(x => x.Key == key).Value ?? String.Empty;
        return item;
    }
}

用于缓存后替换的助手:

using System;
using System.Web;
using System.Web.Mvc;

public static class Html
{
    public delegate object MvcResponseSubstitutionCallback(HttpContextBase context);

    public static object MvcResponseSubstitute(this HtmlHelper html, MvcResponseSubstitutionCallback callback)
    {
        html.ViewContext.HttpContext.Response.WriteSubstitution(
            context =>
                HttpUtility.HtmlEncode(
                    (callback(new HttpContextWrapper(context)) ?? String.Empty).ToString()
                )
            );

        return null;
    }
}

现在这成功了:

<%= Html.MvcResponseSubstitute(context => CustomTempData.Get("message")) %>

如果您了解俄语,请阅读此内容

希望这可以帮助