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浏览器缓存是否可以通过代码清除?

caching browser asp.net c#

Chaddeus · 技术社区 · 14 年前

我的网站上有一个菜单,根据用户是否登录而改变。使用浏览器缓存时,菜单在任何一种状态下都会“卡住”,用户会感到困惑。

他们将登录,但菜单不会更新,因为它仍然缓存在未经验证的状态。。。反之亦然。

更新

下面是如何在我的asp.netmvc 2应用程序:

public class CacheFilterAttribute : ActionFilterAttribute {
    /// <summary>
    /// Gets or sets the cache duration in seconds. The default is 10 seconds.
    /// </summary>
    /// <value>The cache duration in seconds.</value>
    public int Duration { get; set; }

    public CacheFilterAttribute() { Duration = 10; }

    public override void OnActionExecuted(ActionExecutedContext filterContext) {
        if (Duration <= 0) return;

        var cache = filterContext.HttpContext.Response.Cache;
        var cacheDuration = TimeSpan.FromSeconds(Duration);

        cache.SetCacheability(HttpCacheability.Public);
        cache.SetExpires(DateTime.Now.Add(cacheDuration));
        cache.SetMaxAge(cacheDuration);
        cache.AppendCacheExtension("must-revalidate, proxy-revalidate");
    }
}

然后对我的操作应用[CachFilter(Duration=60)]。(注意,上面的代码是从 Kazi Manzur Rashid's Blog

2 回复 | 直到 14 年前

Per Bjurström 14 年前

我一直在玩一个动作过滤器来模拟使用条件请求和电子标签的行为,它是纯客户端缓存,所以这里不涉及输出缓存。您仍然会收到对服务器的请求,但不会调用该操作,如果本地缓存仍然是新的,客户端将使用该缓存。

/// <summary>
/// Handles client side caching by automatically refreshing content when switching logged in identity
/// </summary>
public class ClientCacheByIdentityAttribute : ActionFilterAttribute
{
    /// <summary>
    /// Sets the cache duraction in minutes
    /// </summary>
    public int Duration { get; set; }

    /// <summary>
    /// Check for incoming conditional requests
    /// </summary>
    /// <param name="filterContext"></param>
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if (filterContext.IsChildAction || filterContext.HttpContext.Request.RequestType!="GET" || filterContext.Result!=null)
        {
            return;
        }

        string modifiedSinceString = filterContext.HttpContext.Request.Headers["If-Modified-Since"];
        string noneMatchString = filterContext.HttpContext.Request.Headers["If-None-Match"];

        if (String.IsNullOrEmpty(modifiedSinceString) || String.IsNullOrEmpty(noneMatchString))
        {
            return;
        }

        DateTime modifiedSince;

        if (!DateTime.TryParse(modifiedSinceString, out modifiedSince))
        {
            return;
        }

        if (modifiedSince.AddMinutes(Duration) < DateTime.Now)
        {
            return;
        }

        string etag = CreateETag(filterContext.HttpContext);

        if (etag == noneMatchString)
        {
            filterContext.HttpContext.Response.StatusCode = 304;
            filterContext.Result = new EmptyResult();
        }
    }

    /// <summary>
    /// Handles setting the caching attributes required for conditional gets
    /// </summary>
    /// <param name="filterContext"></param>
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        if (filterContext.HttpContext.Request.RequestType == "GET" && filterContext.HttpContext.Response.StatusCode == 200 && !filterContext.IsChildAction && !filterContext.HttpContext.Response.IsRequestBeingRedirected)
        {
            filterContext.HttpContext.Response.AddHeader("Last-Modified", DateTime.Now.ToString("r"));
            filterContext.HttpContext.Response.AddHeader("ETag", CreateETag(filterContext.HttpContext));
        }
    }

    /// <summary>
    /// Construct the ETag
    /// </summary>
    /// <param name="context"></param>
    /// <returns></returns>
    private static string CreateETag(HttpContextBase context)
    {
        return "\"" + CalculateMD5Hash(context.Request.Url.PathAndQuery + "$" + context.User.Identity.Name) + "\"";
    }

    /// <summary>
    /// Helper to make an MD5 hash
    /// </summary>
    /// <param name="input"></param>
    /// <returns></returns>
    private static string CalculateMD5Hash(string input)
    {
        MD5 md5 = MD5.Create();
        byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(input);
        byte[] hash = md5.ComputeHash(inputBytes);

        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < hash.Length; i++)
        {
            sb.Append(hash[i].ToString("X2"));
        }
        return sb.ToString();
    }
}

tvanfosson 14 年前

article 关于这个话题。