C #: On-line read/write of files and use of File directory dialog boxes

dialog box to read and write files by line
To determine if a file exists: File.exists (string FilePath)
Determine if the directory exists: directory. Exists ("D:\\lastestversion")

To read a file by row:
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 () returns the next available character, but does not use it
{
ListBox1.Items.Add (Sr. ReadLine ());
filecount++;
}
Sr. Close ();

To write a file by line:
StreamWriter sw = new StreamWriter ("D:\\result.txt");
for (int i=0;i<10;i++)
{
Sw. WriteLine ("This is the first" +i.tostring () + "row data");
}

Use of the File Directory dialog box
The file dialog box is the use of filter conditions:
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;

Use of the Directory dialog box:
String Resultfolder= "";
FolderBrowserDialog openfolderdialog1=new FolderBrowserDialog ();
Openfolderdialog1.rootfolder=environment.specialfolder.mycomputer;
if (Openfolderdialog1.showdialog () ==dialogresult.ok)
Resultfolder=openfolderdialog1.selectedpath;