求大神找错

不知道为什么 总是无法提示修改密码 总显示原密码错误 不知道问题出哪了

C# code

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.SqlClient;namespace SuperMarket{    public partial class ModificationPassword : Form    {        public ModificationPassword()        {            InitializeComponent();        }        /// <summary>        /// 修改事件        /// </summary>        /// <param name="sender"></param>        /// <param name="e"></param>        private void button1_Click(object sender, EventArgs e)        {            if (Modification())            {                if (Chose())                {                    MessageBox.Show("修改密码成功！");                }                else                {                    MessageBox.Show("密码修改失败！");                }            }        }        public string username;        public string passwrd;        /// <summary>        /// 修改密码的方法        /// </summary>        /// <returns></returns>        public bool Modification()        {               if (this.textBox1.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请输入原密码！");                this.textBox1.Focus();                return false;            }            if (this.textBox2.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请输入新密码！");                this.textBox2.Focus();                return false;            }            if (this.textBox3.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请输入确认新密码！");                this.textBox3.Focus();                return false;            }            if (this.textBox2.Text != this.textBox3.Text)            {                MessageBox.Show("新密码输入不一致！");                return false;            }            else            {                return true;            }        }        public bool Chose()        {            DBHelper.OpenConnection();            string sql = string.Format("select count(*) from [Users] where UserName='{0}' and PassWord='{1}'",username,this.textBox1.Text.ToString());            SqlCommand com = new SqlCommand(sql, DBHelper.Connection);            try            {                int count = (int)com.ExecuteScalar();                if (count > 0)                {                    sql = string.Format("update [Users] set PassWord='{0}' where UserName='{1}'", this.textBox2.Text.ToString(), username);                    com.CommandText = sql;                    if (com.ExecuteNonQuery() > 0)                    {                        return true;                    }                    else                    {                        return false;                    }                }                else                {                    MessageBox.Show("原密码错误");                    return false;                }            }            catch (Exception)            {                throw;            }            finally            {                DBHelper.CloseConnection();            }        }        /// <summary>        /// 返回事件        /// </summary>        /// <param name="sender"></param>        /// <param name="e"></param>        private void button2_Click(object sender, EventArgs e)        {            DialogResult result = MessageBox.Show("你是否要返回商品管理界面？","提示",MessageBoxButtons.YesNo,MessageBoxIcon.Information);            if (result==DialogResult.Yes)            {                this.Hide();                SuperMarketManage sp = new SuperMarketManage();                sp.Show();            }        }    }} 
 

C# code

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.SqlClient;namespace SuperMarket{    public partial class Login : Form    {        public Login()        {            InitializeComponent();        }        /// <summary>        /// 登录时间        /// </summary>        /// <param name="sender"></param>        /// <param name="e"></param>        private void button1_Click(object sender, EventArgs e)        {            if (ChickMessage())            {                if (ChickLogin())                {                    MessageBox.Show("登录成功!");                    this.Hide();                    SuperMarketManage spu = new SuperMarketManage();                    spu.Show();                }                else                {                    MessageBox.Show("帐号或者密码错误！请重新输入!");                }            }        }        /// <summary>        /// 验证登录的方法        /// </summary>        public bool ChickLogin()        {            bool flag = false;            ModificationPassword mp = new ModificationPassword();            mp.username = this.textBox1.Text.Trim().ToString();            mp.passwrd = this.textBox2.Text.Trim().ToString();            string sql = string.Format("select count(*) from Users where UserName='{0}' and PassWord='{1}'",mp.username,mp.passwrd);                        try            {                DBHelper.OpenConnection();                SqlCommand com = new SqlCommand(sql,DBHelper.Connection);                int count = (int)com.ExecuteScalar();                if (count>0)                {                    flag = true;                }            }            catch (Exception)            {                throw;            }            finally            {                DBHelper.CloseConnection();            }            return flag;        }        /// <summary>        /// 验证是否有输入        /// </summary>        /// <returns></returns>        public bool ChickMessage()        {            if (this.textBox1.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请输入帐号！");                this.textBox1.Focus();                return false;            }            if (this.textBox2.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请输入密码！");                this.textBox2.Focus();                return false;            }            else            {                return true;            }        }        public void Exit()        {            DialogResult result = MessageBox.Show("你是否取消登录并退出！", "提示", MessageBoxButtons.YesNo, MessageBoxIcon.Information);            if (result==DialogResult.Yes)            {                Application.Exit();            }        }        private void button2_Click(object sender, EventArgs e)        {            Exit();        }    }}

[解决办法]
你的ModificationPassword页面，自始自终就没对那个变量username初始化过，一直为空，你倒底要修改谁的密码，它怎么会知道？