NSProgress

NSProgress设计思想

• Foundation Release Notes for OS X v10.11 and iOS 9
  • https://developer.apple.com/library/content/releasenotes/Foundation/RN-Foundation/
• 苹果官方文档的介绍
  • https://developer.apple.com/reference/foundation/nsprogress?language=objc
• 中文请参考（3rd blog）
  • http://www.cocoachina.com/industry/20140522/8518.html
• 英文请参考（3rd blog）
  • https://oleb.net/blog/2014/03/nsprogress/

照着blog写Demo

• http://www.tuicool.com/articles/7zyEjmI
• http://www.jb51.net/article/86774.htm