苹果官网pdf文档，主要介绍了Objective-C Runtime Reference
Apple s official website pdf document introduces the Objective-C Runtime Reference (2013-12-10, Objective-C, 493KB, 下载1次)
苹果官网指定的学习object-c的书籍
Apple s official website designated learning object-c books (2009-01-16, Objective-C, 856KB, 下载8次)