按行读取文件：
int fileCount=0;
// Open the file just specified such that no one else can use it.
StreamReader sr = new StreamReader textBox1.Text.Trim ));
while sr.Peek ) > -1)//StreamReader.Peek )返回下一个可用字符，但不使用它
{
listBox1.Items.Add sr.ReadLine ));
fileCount++;
}
sr.Close );

按行写入文件：
StreamWriter sw = new StreamWriter "D:\\result.txt");
for int i=0;i<10;i++)
{
sw.WriteLine "这是第"+i.ToString )+"行数据");
}

文件目录对话框的使用
文件对话框即过滤条件的使用：
string resultFile="";
OpenFileDialog openFileDialog1 = new OpenFileDialog );
openFileDialog1.InitialDirectory = "D:\\Patch" ;
openFileDialog1.Filter = "All files  *.*)|*.*|txt files  *.txt)|*.txt" ;
openFileDialog1.FilterIndex = 2 ;
openFileDialog1.RestoreDirectory = true ;
if openFileDialog1.ShowDialog ) == DialogResult.OK)
resultFile=openFileDialog1.FileName;

目录对话框的使用：
string resultFolder="";
FolderBrowserDialog openFolderDialog1=new FolderBrowserDialog );
openFolderDialog1.RootFolder=Environment.SpecialFolder.MyComputer;
if openFolderDialog1.ShowDialog )==DialogResult.OK)
resultFolder=openFolderDialog1.SelectedPath;