苹果官方文档
help》documentation》左边iOS》language》objective》the objective-c programming language
系统自带类:core Services Layer
1,安装：装入离线文档 放入Xcode中，Applications/Xcode.app/Contents/development/DocSets
2,Users/用户名/Library/Developer/Shared/Dovumentation/Docsets
苹果官方文档
help》documentation》左边iOS》language》objective》the objective-c programming language
系统自带类:core Services Layer
1,安装：装入离线文档 放入Xcode中，Applications/Xcode.app/Contents/development/DocSets
2,Users/用户名/Library/Developer/Shared/Dovumentation/Docsets