HttpContext.Current.Session 是 null

Question

我在 class 库中有一个带有自定义缓存 object 的网站。 所有项目都运行 .NET 3.5。 I would like to convert this class to use Session state instead of cache, in order to preserve state in a stateserver when my application recycles. 但是，当我访问 Global.asax 文件中的方法时，此代码会引发“HttpContext.Current.Session 为空”异常。 我这样称呼 class ：

Customer customer = CustomerCache.Instance.GetCustomer(authTicket.UserData);

为什么object总是null？

public class CustomerCache: System.Web.SessionState.IRequiresSessionState
{
    private static CustomerCache m_instance;

    private static Cache m_cache = HttpContext.Current.Cache;

    private CustomerCache()
    {
    }

    public static CustomerCache Instance
    {
        get
        {
            if ( m_instance == null )
                m_instance = new CustomerCache();

            return m_instance;
        }
    }

    public void AddCustomer( string key, Customer customer )
    {
        HttpContext.Current.Session[key] = customer;

        m_cache.Insert( key, customer, null, Cache.NoAbsoluteExpiration, new TimeSpan( 0, 20, 0 ), CacheItemPriority.NotRemovable, null );
    }

    public Customer GetCustomer( string key )
    {
        object test = HttpContext.Current.Session[ key ];

        return m_cache[ key ] as Customer;
    }
}

如您所见，我尝试将 IRequiresSessionState 添加到 class 但这并没有什么不同。

干杯詹斯

Answer 1

这并不是要在 class 中包含 State，而是在 Global.asax 中调用它的位置。 Session 并非在所有方法中都可用。

一个工作示例是：

using System.Web.SessionState;

// ...

protected void Application_PreRequestHandlerExecute(object sender, EventArgs e)
    {
        if (Context.Handler is IRequiresSessionState || Context.Handler is IReadOnlySessionState)
        {
            HttpContext context = HttpContext.Current;
            // Your Methods
        }
    }

它不起作用，例如在 Application_Start

Answer 2

根据您要执行的操作，您还可以从使用 Global.asax 中的 Session_Start 和 Session_End 中受益：

http://msdn.microsoft.com/en-us/library/ms178473(v=vs.100).aspx

http://msdn.microsoft.com/en-us/library/ms178581(v=vs.100).aspx

void Session_Start(object sender, EventArgs e)
{
    // Code that runs when a new session is started

}

void Session_End(object sender, EventArgs e)
{
    // Code that runs when a session ends. 
    // Note: The Session_End event is raised only when the sessionstate mode
    // is set to InProc in the Web.config file. If session mode is set to StateServer 
    // or SQLServer, the event is not raised.

}

在依赖 Session_End 之前，请注意对 SessionState Mode 的限制。