C#语法[2] [英] C# grammer[2]
本文介绍了C#语法[2]的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
-Default.aspx--
--Default.aspx--
<%@ 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>无标题页</title>
</head>
<body>
<form id="form1" runat="server">
<asp:Button ID="Button1" runat="server" Height="30px"
Text="Button" Width="69px" onclick="Button1_Click" />
<asp:TextBox ID="TextBox1" runat="server" ></asp:TextBox>
<div>
</div>
</form>
</body>
</html>
--Default.aspx.cs--
--Default.aspx.cs--
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
public delegate void Y();
public partial class _Default : System.Web.UI.Page
{
public event Y X;
protected void Page_Load(object sender, EventArgs e)
{
A a = new A();
X += a.f;
}
protected void Button1_Click(object sender, EventArgs e)
{
X();
}
}
public class A:_Default
{
public void f()
{
TextBox1.Text = "success";
}
}
1)为什么当运行Default.aspx并单击浏览器上的Button时，TextBox1.Text ="success"将在函数f()中生成NullReferenceException.
1)why TextBox1.Text="success" will generate a NullReferenceException in function f() when run Default.aspx and click Button on browser.
推荐答案
创建一个_Default类的实例，但其中的控件未实例化.这是当您请求页面时ASP.NET引擎的作用.
该页面可能会帮助您: http://www.west-wind.com/weblog/posts/120530. aspx [^ ]
Because you just create an instance of class _Default but the controls in it don''t get instantiated. This is what the ASP.NET engine does when you request a page.
This page may help you: http://www.west-wind.com/weblog/posts/120530.aspx[^]
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