将ViewState持久化保持在服务器端

/* from: 没有问题，散分贴：如果你必须开发交互式页面，ViewState越大可能意味着越有本事 */

原作者sp1234 .NET3.0代码

如果你有一个非常酷的页面，页面上很多东西自动地响应用户操作而展现丰富的变化，你的ViewState是很有可能达到200K的。

这里是我将ViewState持久化保持在服务器端的代码，这样ViewState不占用网络带宽，因此其存取只是服务器的磁盘读取时间。并且它很小，可以说是磁盘随便转一圈就能同时读取好多ViewState，因此可以说“不占时间”。为了再“不占磁盘时间”，我还使用了缓存。


一下这段代码可以放在页面中，或者页面的父类中：

protected override object LoadPageStateFromPersistenceMedium()
{
    var viewStateID = (string)((Pair)base.LoadPageStateFromPersistenceMedium()).Second;
    var stateStr = (string)Cache[viewStateID];
    if (stateStr == null)
    {
        var fn = this.Server.MapPath(@"~/App_Data/ViewState/" + viewStateID);        stateStr = File.ReadAllText(fn);
    }
    return new ObjectStateFormatter().Deserialize(stateStr);
}

protected override void SavePageStateToPersistenceMedium(object state)
{
    var value = new ObjectStateFormatter().Serialize(state);
    var viewStateID = (DateTime.Now.Ticks + (long)this.GetHashCode()).ToString(); //产生离散的id号码
     var fn = this.Server.MapPath(@"~/App_Data/ViewState/" + viewStateID);    <br />    //ThreadPool.QueueUserWorkItem(obj => File.WriteAllText(fn, value));
    File.WriteAllText(fn, value);
    Cache.Insert(viewStateID, value);
    base.SavePageStateToPersistenceMedium(viewStateID);
}

不使用Session，因为它会“丢失”。ViewState保存在磁盘上，即使服务器重新启动，也不会丢失页面状态。 
下面这段可以放在Global.asax中，也可以根本不管： 

 

protected void Application_Start(object sender, EventArgs e)
{
    var dir = new DirectoryInfo(this.Server.MapPath("~/App_Data/ViewState/"));
    if (!dir.Exists)
        dir.Create();
    else
    {
        var nt = DateTime.Now.AddHours(-1);
        dir.GetFiles().ForEach(f =>
        {
            if (f.CreationTime < nt)
                f.Delete();
        });
    }
}

46539492修改的.NET2.0代码 

#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  

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();  
            }  
        }