新手提问：Objective-C中在@implementation上加一个@interface的有什么不同？

Question

新手提问，看别人的代码是这样写的：

@interface FirstViewController() 
-(void)timerOnActive;
-(void)getDataFromCD;
@end

@implementation FirstViewController
@synthesize userID;
@synthesize timer;

上面的代码是写在.m文件里的，我的问题是为什么不把

@interface FirstViewController() 
-(void)timerOnActive;
-(void)getDataFromCD;
@end

写在.h文件的@interface中？ FirstViewController() 后面的那个括号是空的，需要填什么吗？这样写是为了补充吗？

Answer 1

The @interface FirstViewController() here is actually a class extension, just like an anonymous category. The methods it declares must be implemented in the main @implementation code block of the corresponding class. A class may have a publicly declared API , while having additional methods declared as private for use only by the class or framework class. You can declare such a method using a category (or more than one category) in a private header file or implementation file mentioned above. This works, but the compiler cannot confirm that all declared methods are implemented.

Answer 2

The method written in the m file cannot be called by external classes. This method is treated as a private method and called within this class. It is hidden from the outside world.