如何查询具有指定特性或名称的文件 (C#)

class FindFileByExtension  
{  
    // This query will produce the full path for all .txt files  
    // under the specified folder including subfolders.  
    // It orders the list according to the file name.  
    static void Main()  
    {  
        string startFolder = @"c:\program files\Microsoft Visual Studio 9.0\";  
  
        // Take a snapshot of the file system.  
        System.IO.DirectoryInfo dir = new System.IO.DirectoryInfo(startFolder);  
  
        // This method assumes that the application has discovery permissions  
        // for all folders under the specified path.  
        IEnumerable fileList = dir.GetFiles("*.*", System.IO.SearchOption.AllDirectories);  
  
        //Create the query  
        IEnumerable fileQuery =  
            from file in fileList  
            where file.Extension == ".txt"  
            orderby file.Name  
            select file;  
  
        //Execute the query. This might write out a lot of files!  
        foreach (System.IO.FileInfo fi in fileQuery)  
        {  
            Console.WriteLine(fi.FullName);  
        }  
  
        // Create and execute a new query by using the previous
        // query as a starting point. fileQuery is not
        // executed again until the call to Last()  
        var newestFile =  
            (from file in fileQuery  
             orderby file.CreationTime  
             select new { file.FullName, file.CreationTime })  
            .Last();  
  
        Console.WriteLine("\r\nThe newest .txt file is {0}. Creation time: {1}",  
            newestFile.FullName, newestFile.CreationTime);  
  
        // Keep the console window open in debug mode.  
        Console.WriteLine("Press any key to exit");  
        Console.ReadKey();  
    }  
}