试试这个

string path = @"c:\mytext.txt";

if (File.Exists(path))
{
    File.Delete(path);
}

{ // Consider File Operation 1
    FileStream fs = new FileStream(path, FileMode.OpenOrCreate);
    StreamWriter str = new StreamWriter(fs);
    str.BaseStream.Seek(0, SeekOrigin.End);
    str.Write("mytext.txt.........................");
    str.WriteLine(DateTime.Now.ToLongTimeString() + " " + 
                  DateTime.Now.ToLongDateString());
    string addtext = "this line is added" + Environment.NewLine;
    str.Flush();
    str.Close();
    fs.Close();
    // Close the Stream then Individually you can access the file.
}

File.AppendAllText(path, addtext);  // File Operation 2

string readtext = File.ReadAllText(path); // File Operation 3

Console.WriteLine(readtext);

在每个文件操作中，文件将被打开并且必须在打开之前关闭.与操作 1 一样，您必须关闭文件流以进行进一步操作.

In every File Operation, The File will be Opened and must be Closed prior Opened. Like wise in the Operation 1 you must Close the File Stream for the Further Operations.