回答編集履歴

  こうでいいと思うのですが、どうでしょうか。

 

  using System;

  using System.IO;

  using System.IO.Compression;

  using System.Linq;

  using System.Text;

  using System.Xml;

  using System.Xml.Linq;

 

  namespace Questions291429

  {

  class Program

  {

  static void Main()

  {

  var xmldoc =

  @"<?xml version=""1.0"" encoding=""UTF-8"" standalone=""yes""?>

  <PCROOT>

  <PInfo Key=""0"">oll</PInfo>

  <PInfo Key=""0"">tll</PInfo>

  <PInfo Key=""1"">ools</PInfo>

  <PInfo Key=""1"">oljl</PInfo>

  <PInfo Key=""1"">ollj</PInfo>

  </PCROOT>";

 

  var xdoc = XDocument.Parse(xmldoc);

  Console.WriteLine(xdoc.ToString());

  GZipCompress(xdoc, @"pc1.gz");

 

  var xdocloaded = GZipDecompress(@"pc1.gz");

  var key0 = xdocloaded.Element("PCROOT")

  .Elements("PInfo")

  .Where(p => p.Attribute("Key").Value == "1");

 

  foreach(var i in key0)

  {

  Console.WriteLine(i.Value);

  }

 

  Console.ReadKey();

  }

 

  static void GZipCompress(XDocument xdin, string gzpath)

  {

  using(var fs = File.Create(gzpath))

  using(var gs = new GZipStream(fs, CompressionMode.Compress))

  // しなくても読めたが中のファイルにBOMが付くのが気持ち悪い場合

  //using(var writer = new XmlTextWriter(gs, new UTF8Encoding(false)))

  {

  //xdin.Save(writer);

  xdin.Save(gs);

  }

  }

 

  static XDocument GZipDecompress(string gzpath)

  {

  using(var fs = new FileStream(gzpath, FileMode.Open, FileAccess.Read, FileShare.Read))

  using(var gs = new GZipStream(fs, CompressionMode.Decompress))

  {

  return XDocument.Load(gs);

  }

  }

  }

  }

  ```