朋友们可以自行测试，我这里都没有问题了，鳖了一上午的问题总算解决了
using system;
using system.collections;
using system.componentmodel;
using system.data;
using system.drawing;
using system.web;
using system.web.sessionstate;
using system.web.ui;
using system.web.ui.webcontrols;
using system.web.ui.htmlcontrols;
using system.xml ;
namespace webapplication1
{
/// <summary>
/// summary description for webform1.
/// </summary>
public class webform1 : system.web.ui.page
{
protected system.web.ui.webcontrols.textbox textbox1;
protected system.web.ui.webcontrols.dropdownlist dropdownlist1;
protected system.web.ui.webcontrols.button button1;
public webform1()
{
page.init += new system.eventhandler(page_init);
}
private void page_load(object sender, system.eventargs e)
{
if(!page.ispostback)
{
//打开某文件(假设web。config在根目录中)
string filename=server.mappath(/) + @/web.config;
xmldocumentxmldoc= new xmldocument();
xmldoc.load(filename);
xmlnodelist topm=xmldoc.documentelement.childnodes;
foreach(xmlelement element in topm)
{
if(element.name.tolower()==appsettings)
{
xmlnodelist _node=element.childnodes;
if ( _node.count >0 )
{
dropdownlist1.items.clear();
foreach(xmlelement el in _node)
{
dropdownlist1.items.add(el.attributes[key].innerxml);
}
}
}
}
}
}
private void page_init(object sender, eventargs e)
{
initializecomponent();
}
#region web form designer generated code
/// <summary>
/// required method for designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void initializecomponent()
{
this.button1.click += new system.eventhandler(this.button1_click);
this.load += new system.eventhandler(this.page_load);
}
#endregion
private void button1_click(object sender, system.eventargs e)
{
string filename=server.mappath(/) + @/web.config;
xmldocumentxmldoc= new xmldocument();
xmldoc.load(filename);
xmlnodelist topm=xmldoc.documentelement.childnodes;
foreach(xmlelement element in topm)
{
if(element.name.tolower()==appsettings)
{
xmlnodelist _node=element.childnodes;
if ( _node.count >0 )
{
foreach(xmlelement el in _node)
{
if(el.attributes[key].innerxml.tolower()==this.dropdownlist1.selecteditem.value.tolower())
{
el.attributes[value].value=this.textbox1.text;
}
}
}
}
}
xmldoc.save(filename);
}
}
}