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 source code ‘messaging/implementation’ program files usually have . 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.

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 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 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 extension M?

An M file is a text file used by MATLAB, an application used for mathematical computations. It can store a script, class, or an individual function in the MATLAB language. M files are used for executing algorithms, plotting graphs, and performing other mathematical operations.

What is Objective-C runtime?

The Objective-C runtime is a runtime library that provides support for the dynamic properties of the Objective-C language, and as such is linked to by all Objective-C apps. Objective-C runtime library support functions are implemented in the shared library found at /usr/lib/libobjc.

What is ID in Obj C?

id is the generic object pointer, an Objective-C type representing “any object”. An instance of any Objective-C class can be stored in an id variable. An id and any other class type can be assigned back and forth without casting: It also means that a method or function parameter typed as id can accept any object.

Can a class extension be added to a class in Objective C?

Objective-C Extensions. A class extension bears some similarity to a category, but it can only be added to a class for which you have the source code at compile time (the class is compiled at the same time as the class extension).

Can a class extension be declared in the implementation block?

The methods declared by a class extension are implemented in the implementation block for the original class, so you can’t, for example, declare a class extension on a framework class, such as a Cocoa or Cocoa Touch class like NSString. Extensions are actually categories without the category name.

Can a class extension be added at compile time?

A class extension bears some similarity to a category, but it can only be added to a class for which you have the source code at compile time (the class is compiled at the same time as the class extension).

What is the difference between category and extension in Objective-C?

A category allows you to add methods to an existing class—even to one for which you do not have the source. Class extensions are similar, but allow additional required APIs to be declared for a class in locations other than within the primary class @interface 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 is the difference between subclassing inheritance vs extension?

The new subclass will inherit all the capabilities of the parent class, but may then be extended to add the missing functionality. Swift extensions provide a useful alternative option to adding functionality to existing classes without the need to create a subclass.

What is a category Objective-C?

What’s the difference between extensions and classes in Objective C?

Categories are an Objective-C language feature that let you add new methods to an existing class. Extensions are a special case of categories that let you define methods that must be implemented in the main implementation block.

How to add a method to a class in Objective-C?

Instead, Objective-C allows you to add your own methods to existing classes through categories and class 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.

When to use a category in Objective C?

=> In Objective C, when you want to add some more functionality to a class without inheritance, you simply use category for it. => it comes with its own .h and .m file => Category uses to add new method not properties.

What’s the difference between category and class 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.