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2026/8/3 20:15:31
在上一篇我们讨论了MVC中使用页面缓存的一些方法，而其中由于页面缓存的粒度太粗，不能对页面进行局部的缓存，或者说，如果我们想在页面缓存的同时对局部进行动态输出该怎么办？下面我们看下这类问题的处理。
MVC中有一个Post-cache substitution的东西，可以对缓存的内容进行替换。
使用Post-Cache Substitution
- 定义一个返回需要显示的动态内容string的方法。
- 调用HttpResponse.WriteSubstitution()方法即可。
示例，我们在Model层中定义一个随机返回新闻的方法。
usingSystem;
usingSystem.Collections.Generic;
usingSystem.Web;
namespaceMvcApplication1.Models
{
publicclassNews
{
publicstaticstringRenderNews(HttpContext context)
{
var news=newList<string>
{
"Gas prices go up!",
"Life discovered on Mars!",
"Moon disappears!"
};
var rnd=newRandom();
returnnews[rnd.Next(news.Count)];
}
}
usingSystem.Collections.Generic;
usingSystem.Web;
namespaceMvcApplication1.Models
{
publicclassNews
{
publicstaticstringRenderNews(HttpContext context)
{
var news=newList<string>
{
"Gas prices go up!",
"Life discovered on Mars!",
"Moon disappears!"
};
var rnd=newRandom();
returnnews[rnd.Next(news.Count)];
}
}
}
然后在页面中需要动态显示内容的地方调用。
<%@ Page Language="C#"AutoEventWireup="true"CodeBehind="Index.aspx.cs"Inherits="MvcApplication1.Views.Home.Index"%>
<%@ Import Namespace="MvcApplication1.Models"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<htmlxmlns="http://www.w3.org/1999/xhtml">
<headrunat="server">
<title>Index</title>
</head>
<body>
<div>
<%Response.WriteSubstitution(News.RenderNews);%>
<hr/>
The content of this page is output cached.
<%=DateTime.Now%>
</div>
</body>
<%@ Import Namespace="MvcApplication1.Models"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<htmlxmlns="http://www.w3.org/1999/xhtml">
<headrunat="server">
<title>Index</title>
</head>
<body>
<div>
<%Response.WriteSubstitution(News.RenderNews);%>
<hr/>
The content of this page is output cached.
<%=DateTime.Now%>
</div>
</body>
</html>
如在上一篇文章中说明的那样，给Controller加上缓存属性。
usingSystem.Web.Mvc;
namespaceMvcApplication1.Controllers
{
[HandleError]
publicclassHomeController : Controller
{
[OutputCache(Duration=60, VaryByParam="none")]
publicActionResult Index()
{
returnView();
}
}
namespaceMvcApplication1.Controllers
{
[HandleError]
publicclassHomeController : Controller
{
[OutputCache(Duration=60, VaryByParam="none")]
publicActionResult Index()
{
returnView();
}
}
}
可以发现，程序对整个页面进行了缓存60s的处理，但调用WriteSubstitution方法的地方还是进行了随机动态显示内容。
对Post-Cache Substitution的封装
将静态显示广告Banner的方法封装在AdHelper中。
usingSystem;
usingSystem.Collections.Generic;
usingSystem.Web;
usingSystem.Web.Mvc;
namespaceMvcApplication1.Helpers
{
publicstaticclassAdHelper
{
publicstaticvoidRenderBanner(thisHtmlHelper helper)
{
var context=helper.ViewContext.HttpContext;
context.Response.WriteSubstitution(RenderBannerInternal);
}
privatestaticstringRenderBannerInternal(HttpContext context)
{
var ads=newList<string>
{
"/ads/banner1.gif",
"/ads/banner2.gif",
"/ads/banner3.gif"
};
var rnd=newRandom();
var ad=ads[rnd.Next(ads.Count)];
returnString.Format("<img src='{0}' />", ad);
}
}
usingSystem.Collections.Generic;
usingSystem.Web;
usingSystem.Web.Mvc;
namespaceMvcApplication1.Helpers
{
publicstaticclassAdHelper
{
publicstaticvoidRenderBanner(thisHtmlHelper helper)
{
var context=helper.ViewContext.HttpContext;
context.Response.WriteSubstitution(RenderBannerInternal);
}
privatestaticstringRenderBannerInternal(HttpContext context)
{
var ads=newList<string>
{
"/ads/banner1.gif",
"/ads/banner2.gif",
"/ads/banner3.gif"
};
var rnd=newRandom();
var ad=ads[rnd.Next(ads.Count)];
returnString.Format("<img src='{0}' />", ad);
}
}
}
这样在页面中只要进行这样的调用，记得需要在头部导入命名空间。
<%@ Page Language="C#"AutoEventWireup="true"CodeBehind="Index.aspx.cs"Inherits="MvcApplication1.Views.Home.Index"%>
<%@ Import Namespace="MvcApplication1.Models"%>
<%@ Import Namespace="MvcApplication1.Helpers"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<htmlxmlns="http://www.w3.org/1999/xhtml">
<headrunat="server">
<title>Index</title>
</head>
<body>
<div>
<%Response.WriteSubstitution(News.RenderNews);%>
<hr/>
<%Html.RenderBanner();%>
<hr/>
The content of this page is output cached.
<%=DateTime.Now%>
</div>
</body>
<%@ Import Namespace="MvcApplication1.Models"%>
<%@ Import Namespace="MvcApplication1.Helpers"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<htmlxmlns="http://www.w3.org/1999/xhtml">
<headrunat="server">
<title>Index</title>
</head>
<body>
<div>
<%Response.WriteSubstitution(News.RenderNews);%>
<hr/>
<%Html.RenderBanner();%>
<hr/>
The content of this page is output cached.
<%=DateTime.Now%>
</div>
</body>
</html>
使用这样的方法可以使得内部逻辑对外呈现出更好的封装。