#region 解决ViewState过于庞大的问题
    protected override object LoadPageStateFromPersistenceMedium()
    {
        string viewStateID = (string)((Pair)base.LoadPageStateFromPersistenceMedium()).Second;
        string stateStr = (string)Cache[viewStateID];
        if (stateStr == null)
        {
            string fn = Path.Combine(this.Request.PhysicalApplicationPath, @"App_Data/ViewState/" + viewStateID);
            stateStr = File.ReadAllText(fn);
        }
        return new ObjectStateFormatter().Deserialize(stateStr);
    }

    protected override void SavePageStateToPersistenceMedium(object state)
    {
        string value = new ObjectStateFormatter().Serialize(state);
        string viewStateID = (DateTime.Now.Ticks + (long)this.GetHashCode()).ToString(); //产生离散的id号码
        string fn = Path.Combine(this.Request.PhysicalApplicationPath, @"App_Data/ViewState/" + viewStateID);
        //ThreadPool.QueueUserWorkItem(File.WriteAllText(fn, value));
        File.WriteAllText(fn, value);
        Cache.Insert(viewStateID, value);
        base.SavePageStateToPersistenceMedium(viewStateID);
    }
    #endregion


或者

可以放在Global.asax中，也可以根本不管：

protected void Application_Start(object sender, EventArgs e)
{

DirectoryInfo dir = new DirectoryInfo(this.Server.MapPath("~/App_Data/ViewState/"));
        if (!dir.Exists)
            dir.Create();
        else
        {
            DateTime nt = DateTime.Now.AddHours(-1);
            foreach(FileInfo f in dir.GetFiles())

{

if (f.CreationTime < nt)
                    f.Delete();
            }
        }

}