What would cause this code to produce a file lock error?

Question

The code below writes to a text file in a while loop and sometimes it will produce an error saying that the "The process cannot access the file because its being used by another process" etc..." The error usually happens on "using (FileStream fs = File.OpenRead(filePath)) " Is there a way to check the file is no longer being used or a way to dispose of the text writer properly?

 if (File.Exists(filePath))
                {
                        TextWriter sud = File.AppendText(filePath);
                        sud.WriteLine(GenericLIST[testloop].ToString());
                        sud.Close();
                        sud.Dispose();
                        using (FileStream fs = File.OpenRead(filePath)) 
                        {
                            using (StreamReader sr = new StreamReader(fs))
                            {
                                while (!sr.EndOfStream)
                                {
                                    richTextBox1.AppendText(sr.ReadLine());
                                }
                            }
                        } 
                    }

                else
                {

                    TextWriter sud = new StreamWriter(filePath);
                    sud.WriteLine(GenericLIST[testloop].ToString());
                    sud.Close();
                    sud.Dispose();
                    }

IMHO, I'd simplify the code to use the various static methods of File (AppendAllText, ReadAllText, WriteAllText) - that's even simpler than remembering to do using's for the TextWriter instances, for instance :) — James Manning
using Windows 7 and tested it on a Windows XP Pro machine as well and it produced the same results. Gonna try James Manning's suggestions sometime tomorrow and see if that works better — Mike

Charlie Charlie · Accepted Answer · 2012-02-16T20:09:04

I've always used:

using (StreamReader reader = new StreamReader(new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)))
{
}

According to MSDN, File.OpenRead is the same as:

new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read)

(the difference being FileShare of Read vs ReadWrite)

What would cause this code to produce a file lock error?

4 Answers