先引用一段apple的解释：
@dynamic
You use the@dynamic keyword to tell the compiler that you will fulfill the API contract implied by a property either by providing method implementations directly or at runtime using other mechanisms such as dynamic loading of code or dynamic method resolution. It suppresses the warnings that the compiler would otherwise generate if it can"t find suitable implementations. You should only use it if you know that the methods will be available at runtime. You use t
@dynamic
You use the@dynamic keyword to tell the compiler that you will fulfill the API contract implied by a property either by providing method implementations directly or at runtime using other mechanisms such as dynamic loading of code or dynamic method resolution. It suppresses the warnings that the compiler would otherwise generate if it can"t find suitable implementations. You should only use it if you know that the methods will be available at runtime. You use t
