synthesize creates setter and getter
(从Objective-C 2.0开始,合成可自动生成存取方法)
the setter is used by IOS to set the pointer of the object on storyboard
we uses getter anytime we want to call the object on storyboard and send messages
属性合成的步骤:
1) 在接口部分(也就是头文件)使用@property指令标识属性
eg: @property int numerator, denominator;
2) 在实现部分使用@synthesize指令
eg: @synthesize numerator, denominator;
3) 然后在实现部分便可使用该属性进行存取
- (void) print { NSLog(@"%i/%i", numerator, denominator); }