using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;

namespace dbclient
{
public partial class monfrm : Form
{
OleDbConnection conn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=ddb.mdb");

string t="";
public monfrm(string t)
{
InitializeComponent();
this.t=t;
}

private void monfrm_Load(object sender, EventArgs e)
{

}

private void button2_Click(object sender, EventArgs e)
{
this.Dispose();
}

private void button1_Click(object sender, EventArgs e)
{
if (textBox2.Text == textBox3.Text)
{
OleDbCommand dc;
int q = 0;
try
{
conn.Open();
dc = new OleDbCommand("select * from denglu where name='" + t + "'", conn);
OleDbDataReader r = dc.ExecuteReader();
if (r.Read())
{
q = r["password"].ToString() == textBox1.Text.ToString() ? 1 : 0;
}

}
finally
{
conn.Close();
}
MessageBox.Show(q.ToString());
try
{

if (q == 1)
{
if (conn.State == ConnectionState.Closed) conn.Open();
string str = "update denglu set password='" + textBox2.Text + "' where name='" + t + "'";
dc = new OleDbCommand(str, conn);

if (dc.ExecuteNonQuery() > 0) 提示出错！
{
MessageBox.Show("Ð޸ijɹ¦£¡");
}
}
else
MessageBox.Show("ÊäÈëÃÜÂë²»ÕýÈ·£¡");

}
finally
{
conn.Close();
}

}
else
MessageBox.Show("Á½´ÎÊäÈë²»Ò»Ö£¡");
}
}
}

提示的错误为：
Exception System.InvalidOperationException was thrown in debuggee:
ExecuteNonQuery 要求已打开且可用的连接。连接的当前状态为已关闭。

CheckStateOpen()
ValidateConnection()
ValidateConnectionAndTransaction()
ExecuteReaderInternal()
ExecuteNonQuery()
button1_Click() - c:\Documents and Settings\Administrator\桌面\chenya\dbserver\dbclient\monfrm.cs:64,25
OnClick()
OnClick()
OnMouseUp()
WmMouseUp()
WndProc()
WndProc()
WndProc()
OnMessage()
WndProc()
DebuggableCallback()
System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop()
RunMessageLoopInner()
RunMessageLoop()
Run()
Main() - c:\Documents and Settings\Administrator\桌面\chenya\dbserver\dbclient\dlfrm.cs:28,13

我想上面的if (conn.State == ConnectionState.Closed) conn.Open();
应该不会错吧，