System.IO.Compression.GZipStream
這個類不能直接用來解壓.zip文件，看看老外怎麽說的
It is possible, with extra code, to produce or read a zip file, with the help of GZipStream, but it is not trivial.
If you want to read or write Zip files, the best bet is to use a third party library, like DotNetZip. This library is free, and enables your applications to read or write zip files that contain multiple compressed files. These are standard zip files that can be opened by Windows Explorer, or WinZip, or other zip tools. It's simple to use. It works with VB, or c#, or any .NET language
總之，如果妳要解壓ZIP文件，還是用第三方庫吧。