干掉xcode 4.2里的performselector警告
xcode 4.2非常可恶，原来的代码里有调用performselector:withObject:的地方无一例外获得一个警告：
Semantic Issue
PerformSelector may cause a leak because its selector is unknown
2012 年 1 月
iOS 5的文件存储策略应对
苹果在iOS 5系统时，对app的文件存储提出了新的要求。从它的guildline来看，是推荐开发者尽量把app生成的文件放在Caches目录下的。原文如下:
Only user-generated data or that cannot otherwise be recreated by your application, should be stored in the /Documents directory and rest should be stored to /Library/Caches directory。