objective-c中的常量类

Question

I have read some posts about constants in Objective-C and I have concluded that is better to create a header and a implementation.

The problem is this. What class should I extend? NSDocument ? Xcode does not allow me to create a class without a subclass.

Answer 1

I guess you mean a place to declare some global constants. If that's the case, then you don't really to define a class.

To be more specific, if your constants are only primitive data and strings. You can define them in a .h file and declare them in a .m file.

Constants.h

extern NSString *const ConstString;
extern const NSInteger ConstInt;

Constants.m

NSString *const ConstString = @"asdasd";
const NSInteger ConstInt = 12;

However, if you need to define constant custom objects. Then you may need a custom singleton class for that. You can reach constants through the singleton's methods. The singelton class should be a subclass of NSObject , because, as @Peter Pei Guo said, that's the base class for all Objective-C classes.

Answer 2

I would say simply extend NSObject .

I do not feel that NSDocument fits the purpose here, since it already has its particular purpose and not related to what you are doing here. According to the document of NSDocument :

The NSDocument abstract class defines the interface for OS X documents. A document is an object that can internally represent data displayed in a window and that can read data from and write data to a file or file package.