按行读写文件
判断文件是否存在:File.Exists(string filePath)
判断目录是否存在:Directory.Exists("D:\\LastestVersion")

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;