title: Creating Excel (.xlsx) files in Cocoa
body: <p>I'm writing a Cocoa application and I'm trying to export to the Excel XML format (ISO/IEC 29500-1) which is basically a zip file with a bunch of XML files in it named with a <code>.xlsx</code> extension.</p>
  
  <p>I've tried generating AppleScript and using <code>NSAppleScript</code> to create the Excel file, which works, but is slow and the user has to have Excel installed on their machine.</p>
  
  <p>I was able to create a simple .xlsx Excel file by writing the XML to files in Objective C and zipping them up and renaming the zip to <code>.xlsx</code>. Excel could open the file, but Numbers threw an error trying to open the file I created. It seems Excel must have implemented all (or most of) the ISO/IEC spec, while Numbers may only open the Excel flavored version.</p>
  
  <p>How to create working Excel files using Cocoa and Objective-c?</p>