Objective-C category (category)

Category is one of the most common functions in objective-C.

Category can add methods for existing classes without adding a subclass.

The standard syntax format of the category interface is as follows:

 
# Import "class name. H" @ Interface Class Name (Class Name) // Declaration of the new method @ end
 

Categories are implemented as follows:

 
# Import "Class Name class name. H" @ implementation class name (Class Name) // new method implementation @ end
 

This is very similar to the class definition. The difference is that category does not have a parent class.And there is a category name in the brackets. The name can be retrieved at will.

For example, if we want to add a method on nsstring to determine whether it is a URL, we can do this:

 
# Import... @ Interface nsstring (utilities)-(bool) isurl; @ end
 

CATEGORY implementation:

 
# Import "nsstringutilities. H "@ implementation nsstring (utilities)-(bool) isurl {If ([self hasprefix: @" http: // "]) return yes; else return no;} @ end
 

Usage:

Nsstring * string1 = @ "http://www.csdn.net"; nsstring * string2 = @ "Pixar"; if ([string1 isurl]) nslog (@ "string1 is a URL "); else nslog (@ "string1 is not a URL"); If ([string2 isurl]) nslog (@ "string2 is a URL "); else nslog (@ "string2 is not a URL ");