重写ViewState的存储目的地,以提高页面性能


在 ASP.NET 中,ViewState 因为在客户端的 HTML 里占据大量的空间,并随着页面的 PostBack 反复传递于网络中,一直为人垢病。但是实际上 ViewState 可以存储到数据库、缓存等任意地方,从而避免频繁将冗长的 base64 字符串发送到客户端。这样做不但可以显着提高性能(大幅度减少了网络传输的字节数),而且如果其中的内容也不会被轻易解密和破解。因此这个方法是很有用处的。

  以下写了一个简单的例子,用缓存来作为 ViewState 存储目的地。至于缓存的 Key,文中给出的只是一个简单的写法,具体可以根据情况给出严密的方案。

  代码大致演示如下:

<%@ Page language="c#" Codebehind="SaveViewStateToOther.aspx.cs" AutoEventWireup="false" Inherits="LinkedList.SaveViewStateToOther" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<html>
 <head>
  <title>SaveViewStateToOther</title>
  <meta name="GENERATOR" Content="Microsoft Visual Studio .NET 7.1">
  <meta name="CODE_LANGUAGE" Content="C#">
  <meta name=vs_defaultClientScript content="JavaScript">
  <meta name=vs_targetSchema content="http://schemas.microsoft.com/intellisense/ie5">
 </head>
 <body MS_POSITIONING="GridLayout">
  <form id="Form1" method="post" runat="server"><asp:DataGrid id=DataGrid1 style="Z-INDEX: 101; LEFT: 104px; POSITION: absolute; TOP: 72px" runat="server" BorderColor="#3366CC" BorderStyle="None" BorderWidth="1px" BackColor="White" CellPadding="4" PageSize="6" AllowPaging="True">
<selecteditemstyle font-bold="True" forecolor="#CCFF99" backcolor="#009999">
</SelectedItemStyle>
  
<itemstyle forecolor="#003399" backcolor="White">
</ItemStyle>
  
<headerstyle font-bold="True" forecolor="#CCCCFF" backcolor="#003399">
</HeaderStyle>
  
<footerstyle forecolor="#003399" backcolor="#99CCCC">
</FooterStyle>
  
<pagerstyle horizontalalign="Left" forecolor="#003399" backcolor="#99CCCC" pagebuttoncount="20" mode="NumericPages">
</PagerStyle>
</asp:DataGrid>
  
   </form>
 </body>
</html>
  
using System;
using System.Data;
using System.IO;
using System.Text;
using System.Web.UI;
using System.Web.UI.WebControls;
  
namespace LinkedList
{
  /// <summary>
  /// SaveViewStateToOther 的摘要说明。
  /// </summary>
  public class SaveViewStateToOther : Page
  {
    protected DataGrid DataGrid1;
  
    private void Page_Load(object sender, EventArgs e)
    {
      if (!IsPostBack)
        Bind();
    }
  
    private void Bind()
    {
      DataTable table = new DataTable();
      table.Columns.Add("id", typeof (int));
      table.Columns.Add("name", typeof (string));
  
      for (int i = 0; i < 1000; i++)
      {
        DataRow row = table.NewRow();
        row["id"] = i;
        row["name"] = "student_" + i.ToString();
        table.Rows.Add(row);
      }
      DataGrid1.DataSource = table;
      DataGrid1.DataBind();
    }
#region Web 窗体设计器生成的代码

    protected override void OnInit(EventArgs e)
    {
      InitializeComponent();
      base.OnInit(e);
    }
  
    private void InitializeComponent()
    {
      this.DataGrid1.PageIndexChanged += new System.Web.UI.WebControls.DataGridPageChangedEventHandler(this.DataGrid1_PageIndexChanged);
      this.Load += new System.EventHandler(this.Page_Load);
  
    }
  
    #endregion
  
    protected override void SavePageStateToPersistenceMedium(object viewState)
    {
      LosFormatter format = new LosFormatter();
      StringWriter writer = new StringWriter();
      format.Serialize(writer, viewState);
      string vsRaw = writer.ToString();
      byte[] buffer = Convert.FromBase64String(vsRaw);
      string vsText = Encoding.ASCII.GetString(buffer);
  
      object v = Cache[PageKey];
      if (v == null)
        Cache.Insert(PageKey, vsText);
      else
        Cache[PageKey] = vsText;
    }
  
    public string PageKey
    {
      get { return Session.SessionID + "_page_SaveViewStateToOther_aspx"; }
    }
  
    protected override object LoadPageStateFromPersistenceMedium()
    {
      object s = Cache[PageKey];
      if (s != null)
      {
        string state = s.ToString();
        byte[] buffer = Encoding.ASCII.GetBytes(state);
        string vsRaw = Convert.ToBase64String(buffer);
        LosFormatter formatter = new LosFormatter();
        return formatter.Deserialize(vsRaw);
      }
      return null;
    }
  
    private void DataGrid1_PageIndexChanged(object source, DataGridPageChangedEventArgs e)
    {
      DataGrid1.CurrentPageIndex = e.NewPageIndex;
      Bind();
    }
  }
}


  对于实际的应用,如果要决定在整个程序中应用此方案,则使用一个通用的页面基类,在其中实现此机制比较合适

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