Question

Possible Duplicate:
How to create global functions in Objective-C

I am curious how it is commonly done to create global utility methods in Objective C that any Class can use.

The simple and only solution I can think of is to simply create a class, i.e. call it GlobalMethods, and just create a bunch of class methods so that they can be used without this class ever getting instantiated.

Is this a wise and valid approach? Regarding the type of methods, they might be anything, for example custom math formulas I use, etc.

Answer 1

There are a few common ways to make some code usable globally. Here are some, with examples from Apple’s public APIs:

• Create class methods on a new class. This is what you suggested. Examples: NSPropertyListSerialization, NSJSONSerialization.

• Create class methods on some appropriate existing class. Example: UIKit uses a category to add class methods to NSValue, such as valueWithCGRect: and valueWithCGPoint:.

• Create a singleton that understands some group of related messages. Examples: [UIApplication sharedApplication], [NSFileManager defaultManager].

• Create plain old C functions. Examples: UIImagePNGRepresentation, UIRectFill, NSLog, NSStringFromCGPoint, and a pantload more.

• If the code operates on some object in particular, add a method the the object’s class using a category. Example: UIKit adds sizeWithFont:, drawAtPoint:withFont:, and related methods to NSString using a category.