What is a category in Objective C and when is it used?

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.

To add a category, go to File -> New File…, and select “ObjectiveC category” from the “Cocoa Touch” tab under iOS. This will bring up an additional window, where you can name the Category in the “Category” textfield. You then type or select the class you want to add it to, and it will output 2 very simple files.

Furthermore, what is posing in Objective C? ObjectiveC Posing. ObjectiveC permits a class to wholly replace another class within a program. The replacing class is said to “pose as” the target class. For the versions that supported posing, all messages sent to the target class are instead received by the posing class.

Likewise, what is the difference between category and extension in Objective C?

Categories are an ObjectiveC 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.

What is category in iOS?

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 in Objective 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 difference between category and extension in iOS?

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 a protocol in Objective C?

Objective-C allows you to define protocols, which declare the methods expected to be used for a particular situation. If you need a class to adopt multiple protocols, you can specify them as a comma-separated list. We have a delegate object that holds the reference of the calling object that implements the protocol.

What is category in iOS Swift?

In Objective C they were called categories, but in Swift they are called extensions. The purpose of both of them are to give additional functionality to existing classes without having to create subclasses.

How do I create a class in Xcode?

How To Create Custom Class In Xcode Project Click File —> New —> File menu item in the Xcode top menu bar. Then select iOS tab at top tab bar of the popup window, then select Cocoa Touch Class item in the Source section. Click Next button to go to next dialog window. Choose a folder to save the custom class related files.

What is Objective C used for?

Objective-C is an object-oriented programming language that is used to derive OS X and iOS and their APIs. Objective-C programming is a programming language that is used for general purpose activities. While it is not specific to any particular platform or system, it can greatly aid a variety of other frameworks.

What is a category extension?

Definition: 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 is the difference between class and category?

As nouns the difference between category and class is that category is a group, often named or numbered, to which items are assigned based on similarity or defined criteria while class is (countable) a group, collection, category or set sharing characteristics or attributes.

What is unnamed category in IOS?

The anonymous category is an additional Objective C feature that provides an alternate way to declare private methods.

What is extension in Swift?

Swift Extension is a useful feature that helps in adding more functionality to an existing Class, Structure, Enumeration or a Protocol type. This includes adding functionalities for types where you don’t have the original source code too (extensions for Int, Bool etc.

What are the differences between copy and retain?

Retain increases the retain count of an object by 1 and takes ownership of an object. Whereas copy will copy the data present in the memory location and will assign it to the variable so in the case of copy you are first copying the data from a location assign it to the variable which increases the retain count.

What are iOS protocols?

By definition a protocol clarifies sets of methods that can be implemented by any class for an iOS app. Protocols are used to define interfaces that are implemented by classes. When a class implements the methods in a protocol, the class is said to conform to the protocol.

What is protocol in iOS Swift?

Source : Apple Docs. A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality. The protocol can then be adopted by a class, structure, or enumeration to provide an actual implementation of those requirements.