又来C#读取INI问题

Question

因为我要根据读取的情况，作出下列的写法：using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.IO;
using System.Text.RegularExpressions;namespace WinTest
{
    public partial class Form3 : Form
    {
        private string replaceValue = null;
        private string iniKey = string.Empty;
        private StreamReader sr = null;
        private string section = string.Empty;
                public Form3()
        {
            InitializeComponent();
        }        private void butDis_Click(object sender, EventArgs e)
        {
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                try
                {
                    sr = new StreamReader(openFileDialog1.FileName);
                    section = sr.ReadLine();
                    if (section.IndexOf('[') < 0)
                        throw new Exception();
                    section = section.Substring(section.IndexOf('[') + 1, section.IndexOf(']') - 1);
                    iniKey = sr.ReadLine();
                    iniKey = iniKey.Substring(0, iniKey.IndexOf('='));
                    this.textFileName.Text = openFileDialog1.FileName;
                    StringBuilder temp = new StringBuilder(255);
                    int i = GetPrivateProfileString(section, iniKey, "", temp, 255, this.textFileName.Text);
                    this.textDis.Text = temp.ToString();
                }
                catch (Exception ex)
                {
                    MessageBox.Show("This isn't legal ini file!");
                    return;
                }
            }
        }        private void butModify_Click(object sender, EventArgs e)
        {
            if (this.textFileName.Text.Equals(""))
                MessageBox.Show("沒有信息", "information");
            else if (this.textFileName.Text.Equals(""))
                MessageBox.Show("沒讀取文件！", "information");
            else
            {
                WritePrivateProfileString(section, iniKey, this.textDis.Text, this.textFileName.Text);
                MessageBox.Show("成功寫入!", "information");
            }
        }
        [DllImport("kernel32")]
        private static extern long WritePrivateProfileString(string section, string key, string val, string filePath);        [DllImport("kernel32")]
        private static extern int GetPrivateProfileString(string section, string key, string def, StringBuilder retVal, int size, string filePath);        
                private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                iniKey = sr.ReadLine();
                if (iniKey.IndexOf('[') < 0)
                {
                    iniKey = iniKey.Substring(0, iniKey.IndexOf('='));                    StringBuilder temp = new StringBuilder(255);
                    int i = GetPrivateProfileString(section, iniKey, "", temp, 255, this.textFileName.Text);
                    this.textDis.Text = temp.ToString();
                }
                else
                {
                    section = iniKey.Substring(iniKey.IndexOf('[') + 1, iniKey.IndexOf(']') - 1);
                    StringBuilder temp = new StringBuilder(255);
                    int i = GetPrivateProfileString(section, iniKey, "", temp, 255, this.textFileName.Text);
                    
                }
                
            }
            catch (Exception ex)
            {
                MessageBox.Show("at the end!");
            }
        }        
    }
}
但现在却保存不了，到底为什么呢？以前我直接在函数里指定section和key的时候是可以，为什么现在这样写就保存不了呢？