ASP.Net会话中的静态单例

Static Singleton In ASP.Net Session

我一直在读ASP.NET中关于单例的内容，我看到了各种实现和建议。我尝试在这之后对我的实现进行建模：https://stackoverflow.com/…asp-net-singleton

这是我的问题：我想要一个我正在实例化的对象，以维持当前会话的生命，但不能在会话之间共享。例如，如果两个用户同时登录，我希望他们各自"拥有"一个全局对象的实例。下面是我的实现。这是正确的方法吗？

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public class AppGlobal
{
#region Contructors

public AppGlobal() { }

public static AppGlobal Instance
{
get
{
HttpSessionState session = HttpContext.Current.Session;

if (session["AppGlobalInstance"] == null)
{
session["AppGlobalInstance"] = new AppGlobal();
}

return (AppGlobal)session["AppGlobalInstance"];
}
}

#endregion

#region Public Properties

public User UserObject { get; set; }
public Campaign CampaignObject { get; set; }
public List<int> SelectedContactIDs = new List<int>();
public List<int> UnsubmittedContactIDs = new List<int>();
public List<int> SubmittedContactIDs = new List<int>();
public List<int> ProcessedContactIDs = new List<int>();

#endregion

#region Public Instance Methods

public void ClearCampaign()
{
CampaignObject = null;
UnsubmittedContactIDs.Clear();
SubmittedContactIDs.Clear();
ProcessedContactIDs.Clear();
SelectedContactIDs.Clear();
}
public void LoadCampaign(int campaignID)
{
//Ensure that old data is overwritten
MailCampaignManagerEntities db = new MailCampaignManagerEntities();

db.Campaigns.MergeOption = System.Data.Objects.MergeOption.OverwriteChanges;

//Clear the campaign and associated data
ClearCampaign();

//Set campaign object in AppGlobal
this.CampaignObject = db.Campaigns.SingleOrDefaultasp.net(x => x.CampaignID == campaignID);

//Populate Contact Status Lists
this.UnsubmittedContactIDs.AddRange(from x in this.CampaignObject.CampaignContacts
where x.ContactSubmissionID == null
select x.CampaignContactID);

this.SubmittedContactIDs.AddRange(from x in this.CampaignObject.CampaignContacts
where x.ContactSubmissionID != null
select x.CampaignContactID);

this.ProcessedContactIDs.AddRange(from x in this.CampaignObject.CampaignContacts
where x.ContactSubmissionID != null
&& x.ContactSubmission.DateProcessed != null
select x.CampaignContactID);
}

#endregion

#region Public Static Methods

public static void WriteLogEntry(int? campaignID, int? contactSubmissionID, int? scheduledDropID, int? userID, string activityDescription)
{
ActivityLog activityLog = new ActivityLog();
activityLog.CampaignID = campaignID;
activityLog.ContactSubmissionID = contactSubmissionID;
activityLog.ScheduledDropID = scheduledDropID;
activityLog.UserID = userID;
activityLog.Text = activityDescription;
activityLog.CreatedDate = DateTime.Now;

using (MailCampaignManagerEntities db = new MailCampaignManagerEntities())
{
db.ActivityLogs.AddObject(activityLog);
db.SaveChanges();
}
}

#endregion
}

实现通常应该是"好的"，但是…

您应该根据配置的sessionstatemodule将对象标记为[Serializable]。Web场或Web花园通常使用InProc之外的模块，它们使用序列化来存储会话状态。否则，对象看起来可以序列化，因此没有问题。

您可能需要检查当前是否有任何会话，或者您可以获得一个NullReferenceException。这可能意味着应用程序配置错误，或者生命周期中的调用太早。

由于在检查和设置会话变量的过程中存在竞争条件，应用程序可能会为单个会话分配两次AppGlobal对象。我不认为这是一个问题，但如果你想包括更多的花哨的东西，这是需要记住的。为了防止出现这种情况，您可以这样使用lock：

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public class AppGlobal
{
private static object _syncRoot = new object();

public static AppGlobal Instance
{
get
{
HttpSessionState session = HttpContext.Current.Session;

lock (_syncRoot)
{
if (session["AppGlobalInstance"] == null)
{
session["AppGlobalInstance"] = new AppGlobal();
}
}

return (AppGlobal)session["AppGlobalInstance"];
}
}
}

如果要在对象中存储禁止序列化的内容，并且需要支持其他sessionstatemodules，可以将实例存储在使用经典单例模式的集合中(这里是一个很好的实现)。同时行动可能是个不错的选择。作为密钥，您可以使用一些您在会话中存储的独特的东西，比如guid。当会话以任何方式结束时，需要从集合中删除该条目。