[c#] How to get relative path of a file in visual studio?

I think using this will be the easiest

new Uri("pack://application:,,/FolderIcon/" + youImageICO);

or this code will work on any machine that if your folder is in your root project if you want to change it... just change this section @"..\"

public static string bingPathToAppDir(string localPath)
{
    string currentDir = Environment.CurrentDirectory;
    DirectoryInfo directory = new DirectoryInfo(
        Path.GetFullPath(Path.Combine(currentDir, @"..\..\" + localPath)));
    return directory.ToString();
}