Why is this function returning nothing, although there is a match?

Question

I am calling this (Compact Framework - this code runs on a Windows CE handheld device) method:

public static List<string> GetXMLFiles(string fileType, string startingDir)
{
    const string EXTENSION = ".XML";
    string dirName = startingDir; 
    var fileNames = new List<String>();
    try
    {
        foreach (string f in Directory.GetFiles(dirName))
        {
            string ext = Path.GetExtension(f).ToUpper();
            string fileNameOnly = Path.GetFileNameWithoutExtension(f);
            if ((ext.Equals(EXTENSION, StringComparison.OrdinalIgnoreCase)) && (fileNameOnly.Contains(fileType)))
            {
                fileNames.Add(f);
            }
        }
        foreach (string d in Directory.GetDirectories(dirName))
        {
            GetXMLFiles(fileType, d);
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
    return fileNames;
}

...like so:

List<String> XMLFiles = CCRUtils.GetXMLFiles(fileType, "\\");
MessageBox.Show(XMLFiles.Count.ToString());

...yet it's returning nothing (MessageBox shows "0"), even though there is a file that matches fileType and has an .xml extension.

Is it because there's something wrong with my GetXMLFiles() method? According to one cat here, my method is fouled up, and I should be adding to the generic list of string (fileNames) more often.

If he's right, I don't get that, though, because it seems to me that this is how the method should work:

(a) The first foreach loop looks at files below the root; if a match is found, it's added to the generic list of string
(b) The second foreach loop makes a recursive call to its method, once for every subdirectory on the device; step "a" occurs again for that directory, adding any matches to the generic list of string.

In this way, all directories are searched, and any matches found are added to the generic list of string (fileNames).

After the second foreach loop runs its course/handles all directories, control drops to the final line of code, which returns fileNames to the caller.

So, according to my grokking of it, I should get the match returned, but I'm getting nothing whatsoever.

If I'm wrong and Alan is right, where should I be adding the additional call to add/how should this method be reworked?

UPDATE

Calling it like this:

List<String> XMLFiles = CCRUtils.GetXMLFiles(fileType, "\\");

...doesn't work, but this way does:

List<String> XMLFiles = CCRUtils.GetXMLFiles(fileType, @"\");

Answer 1

In your recursion, you are losing the files you find in the subdirectories. Capture the return filenames this way:

foreach (string d in Directory.GetDirectories(dirName))
{
    fileNames.AddRange(GetXMLFiles(fileType, d));
}

What is going on is that this line var fileNames = new List<String>(); creates a local variable called fileNames. You may think because your method is static, the variables inside the method are static. This is not the case. So, each time you call GetXMLFiles, a copy of this variable is created for each call.

Since fileNames is local to each call of GetXMLFiles, you need to return to the caller all the fileNames it finds and the caller needs to add those to the collection that is local to it.