1. @property中的 @synthesize 和 @dynamic 区别：
@synthesize will generate getter and setter methods for your property.
@synthesize 能够为你的属性自动生成getter和setter方法。
@dynamic just tells the compiler that the getter and setter methods are implemented not by the class itself but somewhere else(like the superclass)
@dynamic 会告诉编译器：getter和setter方法在别处生成了（比如父类中），并没有在本类生成。
Uses for @dynamic are e.g. with subclasses of NSManagedObject(CoreData) or when you want to create an outlet for a property defined by a superclass that was not defined as an outlet;
运行时动态创建绑定：主要使用在CoreData的实现NSManagedObject子类时使用，由Core Data框架在程序运行的时动态生成子类属性。
