Question

I’m trying to find out if a file exists, if it does, verify if the css style already exists, if not, write them at the end of the file …

I’m doing all this already but in 3 steps:

Does the file exist?

FileInfo fi= new FileInfo(Path.Combine(rootPath, "DefaultStyles.css");

If it does, I use TextReader to get the contents

using (TextReader tr = new StreamReader(file))
{
    r = tr.ReadToEnd().Contains(".onebyonecard");
    tr.Close();
}

Then I write into it if style was not found

using (TextWriter tw = new StreamWriter(file))
{
    tw.Write(cssStyle);
    tw.Close();
}

Is there a way to do this in one easy open / close, instead needed to open the file over and over?

Answer 1

Well you can open a single stream for read and write – but given that you’re reading the whole file, I would personally just open it twice. Note that your current code will overwrite the file, not append to it.

I would personally use the static methods in the File class:

// Elide this into the "if" condition if you want. I've separated it out here,
// but obviously it makes no difference.
bool present = File.Exists(path) &&
               File.ReadAllText(path).Contains(".onebyonecard);
if (!present)
{
    File.AppendAllText(path, cssStyle);
}

This is simpler than having a read/write stream and creating both a TextReader and a TextWriter over it.

A couple of notes:

• By separating the file access, there is a slight risk of a race condition. We could open the file, read the contents, then it could be updated while we decide what to do next. Likewise the file could exist when we perform the check, but then be deleted before it’s read. In most applications this risk is so slight as to be irrelevant – only you can say for sure.
• The code above could still throw an exception, if the file exists but can’t be read/written by the relevant user, or is in use by another process. Normal exception handling style applies – decide to what extent you think you can actually recover from such situations, and act appropriately.