Category, categories

Category, categories

Category
When I encapsulate a class and don't want to modify it any more, but as the program function increases, we need to add a new method to that class. This is just to add a category of this class) you can.
Note: The category definition method will become part of the original class. the category method defined by the parent class. Its subclass inherits. If a Category method is added to a subclass, the parent class does not have the category method of the subclass.
CATEGORY applications:
Extends existing classes
As an alternative to subclass
Classify methods in the class
CATEGORY limitations:
You cannot add new instance variables to a category.
The method in the override class may cause the break of the super message. Because the method in the category has a higher priority, do not overwrite the method of the existing class.


Creation method:
I. Add a new class
Before xcode6
Create a file -- Cocoa Touch -- Objective-C category;
After xcode6
Create a file -- Objective-C file -- file type: Select Category
Ii. Create in code
@ Interface parent class name (custom name)
@ End