[转载]浅谈ASP.NET的Postback-优快云博客

说道ASP.NET的Postback，就得说Web Page的生命周期，但是Web Page的生命周期却不是三言两语就能够说得清楚的，所以在这里单纯站的编程的角度，撇开Web Page 的生命周期浅谈Postback。

我们知道，无论是ASP.NET1.x,2.0，甚至是以后的版本，ASP.NET最终Render到Client端通过浏览器浏览的都是一样：一个单纯的HTML。Client通过Submit Form的方式将填入Form的数据提交给Server进行处理。我们现在来看看ASP.NET整个Postback程序处理的过程。

首先我们通过一个Sample来看ASP.NET如何处理一个通过Click一个Button引起的Postback。下面是Web Page的HTML：

<@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Test Page</title>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <asp:Label runat="server" ID="LabelMessage" ForeColor="red"></asp:Label>
        </div>
        <div>
            <asp:Button runat="server" ID="Button1" Text="Button1" OnClick="Button1_Click" OnCommand="Button_Command"      CommandArgument="Button1" />
            <asp:Button runat="server" ID="Button2" Text="Button2" OnClick="Button2_Click" OnCommand="Button_Command"     CommandArgument="Button2" UseSubmitBehavior="false" />
            <asp:Button runat="server" ID="Button3" Text="Button3" OnClick="Button3_Click" OnCommand="Button_Command"     CommandArgument="Button3" UseSubmitBehavior="false" />
        </div>
    </form>
</body>
</html>
很简单，定义了3个Button，分别注册了他们的两个Event：Click和Command。3个Button的Command Event Hander是一样的：Button_Command，通过指定的CommandArgument来让Event Handler判断到底是哪个Button触发了Command Event。

下面是Code Behind：

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class _Default : System.Web.UI.Page
{

    protected void Page_Load(object sender, EventArgs e)
    {

     }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string message = string.Format("The {0} event of {1} is fired", "Click", "Button1");
        this.LabelMessage.Text = message;
     }
    protected void Button2_Click(object sender, EventArgs e)
    {
        string message = string.Format("The {0} event of {1} is fired", "Click", "Button2");
        this.LabelMessage.Text = message;
     }
    protected void Button3_Click(object sender, EventArgs e)
    {
        string message = string.Format("The {0} event of {1} is fired", "Click", "Button3");
        this.LabelMessage.Text = message;
     }

    protected void Button_Command(object sender, CommandEventArgs e)
    {
        string message = string.Format("The {0} event of {1} is fired", "Command", e.CommandArgument);
        this.LabelMessage.Text += "; " + message;
     }
}