可能重复:
Objective-C: Class vs Instance Methods?
What do the plus and minus signs mean in Objective C next to a method?+(无效)或 - (无效)差异?
我试着环顾四周,并不能拿出一个坚实的答案,真正解释了我的困惑。我见过几次,这是具有有它的“方法类型”设置方法,一类为“+”,即:-(Fraction*) fractionWithNumerator: (int) n denominator: (int) d;
现在如何不同,以+(Fraction*) fractionWithNumerator: (int) n denominator: (int) d;
请参阅在方法旁边,Objective C中的加号和减号是什么意思? ](http://stackoverflow.com/questions/2097294/what-do-the-plus-and-minus-signs-mean-in-objective-c-next-to-a-method) – 2010-07-09 19:42:15
这个人回答了它的me:http://stackoverflow.com/questions/1053592/objective-c-class-vs-instance-methods – jsherk 2012-07-15 17:40:04