asp.net|技巧|性能|页面
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。这样做不但可以显著提高性能（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。
出处：木野狐 BLOG