Question

I have a program that roughly does this:

1. open a file to read from it.
2. close the file
3. Start a filewatcher to watch for changes in the file.
4. As soon as a change is detected, the filewatcher’s EnableRaisingEvents flag is set to false and the process repeats from Step 1.

The problem is, after going from step 4 to step 1, it cannot read the file saying that it is being used by another Process.

Error I receive:

Unhandled Exception: System.IO.IOException: The process cannot access the file ‘c:\test.xml’ because it is being used by another process.

Whats going wrong? does the reader from Step 1 of my program still have the file open, or is some entirely different process accessing the file, or is it that filewatcher is still watching the file after moving to Step 1 from 4, despite setting the flag to false?

Answer 1

If your code is similar to this:

[STAThread]
static void Main(string[] args)
{
    string file = "temp.txt";
    ReadFile(file);
    FileSystemWatcher fswatcher = new FileSystemWatcher(".\\");
    fswatcher.Changed += delegate(object sender, FileSystemEventArgs e)
                             {
                                 ReadFile(e.FullPath);
                             };
    while (true)
    {
        fswatcher.WaitForChanged(WatcherChangeTypes.Changed);
    }
}
private static void ReadFile(string file)
{
    Stream stream = File.OpenRead(file);
    StreamReader streamReader = new StreamReader(stream);
    string str = streamReader.ReadToEnd();
    MessageBox.Show(str);
    streamReader.Close();
    stream.Close();
}

If you are editing the file via notepad, then, when you click the save button, it keeps the file open, while as if when you just close the program and click save it doesn’t. I do no know if this is a bug or an undocumented feature of notepad, but this just might be your problem. One way to fix this is to do the following:

In your anonymous delegate, or wherever you execute the call to ReadFile() call Thread.Sleep(1000), to have the program wait before reading the file and your code should work fine.