2 Answers. A category allows you to add methods to an existing class—even to one for which you do not have the source. There is a section in the Objective-C 2.0 programming Language document about Categories and Extensions.
How do you add a category in Objective-C?
Objective-C Language Categories Create a Category on XCode Open your XCode project, click on File -> New -> File and choose Objective-C file , click Next enter your category name say “CustomFont” choose file type as Category and Class as UIFont then Click “Next” followed by “Create.”
What is the difference between category and extension in Objective-C?
Categories are an Objective-C language feature that let you add new methods to an existing class, much like C# extensions. Objective-C’s extensions are a special case of categories that let you define methods that must be declared in the main implementation block.
What is Objective-C extension?
Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. m filename extensions, while Objective-C ‘header/interface’ files have . h extensions, the same as C header files. Objective-C++ files are denoted with a . mm file extension.
What are categories used for in C?
Categories provide the ability to add functionality to an object without subclassing or changing the actual object. A handy tool, they are often used to add methods to existing classes, such as NSString or your own custom objects.
What is the difference between category VS extension?
Category and extension both are basically made to handle large code base, but category is a way to extend class API in multiple source files while extension is a way to add required methods outside the main interface file.
What is Objective-C category?
In order add such extension to existing classes, Objective-C provides categories and extensions. If you need to add a method to an existing class, perhaps, to add functionality to make it easier to do something in your own application, the easiest way is to use a category.
What can be achieved with category and extension?
A category allows you to add methods to an existing class—even to one for which you do not have the source. Categories are a powerful feature that allows you to extend the functionality of existing classes without subclassing.
What is a category extension when is it used?
What is Category Extension? Category or Brand Extension is a strategy by which, a company uses the same brand to enter into a completely unrelated product segment. The company leverages on the brand equity and success of its existing brand to introduce the new product to increase market acceptance.
What are function categories?
The various types of functions are as follows:
- Many to one function.
- One to one function.
- Onto function.
- One and onto function.
- Constant function.
- Identity function.
- Quadratic function.
- Polynomial function.
What are the two 2 categories of functions?
Function with no arguments and no return value. Function with no arguments and a return value. Function with arguments and no return value.
What are extensions in Objective C?
Extensions are actually categories without the category name. It’s often referred as anonymous categories. The syntax to declare a extension uses the @interface keyword, just like a standard Objective-C class description, but does not indicate any inheritance from a subclass.
What is Objective-C language used for?
Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. This is the main programming language used by Apple for the OS X and iOS operating systems and their respective APIs, Cocoa and Cocoa Touch.
How do you declare a category in Objective-C?
The syntax to declare a category uses the @interface keyword, just like a standard Objective-C class description, but does not indicate any inheritance from a subclass. Instead, it specifies the name of the category in parentheses, like this −
How to add methods to an existing class in Objective-C?
In order add such extension to existing classes, Objective-C provides categories and extensions. If you need to add a method to an existing class, perhaps, to add functionality to make it easier to do something in your own application, the easiest way is to use a category.
