學科:IOS/KB/編譯警告

No previous prototype for function

參考：http://stackoverflow.com/q/7076345

PerformSelector may cause a leak because its selector is unknown

參考：http://stackoverflow.com/q/7017281

Switch case is in protected scope

原因：switch case塊里不允許定義變量

參考：http://stackoverflow.com/q/92396