Directory.GetFiles of certain extension

If you would like to do your filtering in LINQ, you can do it like this:

var ext = new List<string> { "jpg", "gif", "png" };
var myFiles = Directory
    .EnumerateFiles(dir, "*.*", SearchOption.AllDirectories)
    .Where(s => ext.Contains(Path.GetExtension(s).TrimStart(".").ToLowerInvariant()));

Now ext contains a list of allowed extensions; you can add or remove items from it as necessary for flexible filtering.

Doesn't the Directory.GetFiles(String, String) overload already do that? You would just do Directory.GetFiles(dir, "*.jpg", SearchOption.AllDirectories)

If you want to put them in a list, then just replace the "*.jpg" with a variable that iterates over a list and aggregate the results into an overall result set. Much clearer than individually specifying them. =)

Something like...

foreach(String fileExtension in extensionList){
    foreach(String file in Directory.GetFiles(dir, fileExtension, SearchOption.AllDirectories)){
        allFiles.Add(file);
    }
}

(If your directories are large, using EnumerateFiles instead of GetFiles can potentially be more efficient)