Top 35+ Objective-C Interview Questions & Answers [ FRESHERS ]

Last updated on 04th Jul 2020, Blog, Interview Questions

Objective-C is a programming language primarily used for developing macOS and iOS applications. It’s an extension of the C language with Smalltalk-style object-oriented programming capabilities. Objective-C combines the efficiency of C with object-oriented features, allowing developers to write both procedural and object-oriented code. It was the main language for Apple development before the introduction of Swift. The syntax involves square brackets for method invocation and a dynamic runtime that enables features like message passing between objects.

1. What is Objective-C?

Ans:

Objective-C is a programming language developed by Apple for macOS and iOS development. It extends the C programming language with Smalltalk-style object-oriented programming capabilities. Objective-C’s syntax is influenced by C, and it uses a Smalltalk-style object model, making it dynamic and capable of supporting object-oriented principles. The language includes features like dynamic typing, message-passing, and runtime reflection. Developers often encounter Objective-C code when working with older iOS or macOS projects or using certain legacy frameworks.

2. Explain the difference between a class and an object in Objective-C.

Ans:

• A class is a blueprint for creating objects, while an object is an instance of a class. Classes define the structure and behavior; objects are instances created based on these definitions.
• In Objective C, a class is a blueprint or template that defines the properties and behaviors common to a group of objects. On the other hand, an object is an instance of a class, representing a specific realization of those properties and behaviors.
• Classes provide a way to structure code and encapsulate functionality, while objects are the actual instances created based on those class definitions.

3. What is the significance of the @synthesize directive in Objective-C?

Ans:

In Objective-C, @synthesize generates getter and setter methods automatically for properties declared in a class, reducing the need for manual implementation. With @synthesize, you can simplify your code by letting the compiler generate the accessor methods, reducing the boilerplate code in your class implementation. It’s particularly useful when working with properties to encapsulate access to instance variables, enhancing code readability and maintainability.

4. How does memory management work in Objective-C?

Ans:

• Objective-C traditionally used manual reference counting for memory management. Developers were responsible for retaining and releasing objects. With the introduction of Automatic Reference Counting (ARC), the compiler handles much of this manual memory management.
• Objective-C uses Automatic Reference Counting (ARC) for memory management. It automatically tracks and releases objects when no longer needed, minimizing manual memory management tasks.

5. What is the purpose of the @autoreleasepool block in Objective-C?

Ans:

@autoreleasepool defines a scope in which temporary objects are automatically released. It helps manage memory more efficiently, especially when creating many temporary objects. The @autoreleasepool block in Objective-C is used to manage the memory pool efficiently. It helps reduce memory footprint by automatically releasing objects that are no longer needed, thus improving memory management in iOS and macOS development.

6. Explain the difference between categories and extensions in Objective-C.

Ans:

Categories:

• Purpose: Add methods to existing classes.
• Access to Instance Variables: No additional instance variables.
• Usage: Extending functionality.

Extensions:

• Purpose: Declare private methods and properties.
• Access to Instance Variables: You can add instance variables.
• Usage: Often used for internal class enhancements.

7. What is the delegate pattern in Objective-C?

Ans:

• The delegate pattern involves one object (the delegate) acting on behalf of another. It’s commonly used to handle events or messages between objects. Delegates are often used in frameworks like UIKit for handling user interactions. In Objective-C, the delegate pattern involves one object (the delegate) acting on behalf of another.
• The delegating object sends messages to the delegate to notify or consult about certain events or decisions. This pattern promotes loose coupling between objects, enhancing modularity and maintainability in software design.

8. What is KVC (Key-Value Coding) in Objective-C?

Ans:

KVC is a mechanism that allows accessing an object’s properties using string-based keys. It provides a way to dynamically set and get property values, making code more flexible and adaptable. Key-value coding (KVC) in Objective-C is a mechanism that allows indirect access to an object’s properties using string-based keys. Instead of directly invoking methods to get or set a property, KVC enables you to access properties dynamically. It simplifies code and is often used in scenarios like data binding and generic algorithms.

9. Explain the concept of protocols in Objective-C.

Ans:

• Protocols define a set of methods that a class can choose to implement. They serve as a blueprint for methods that classes adopting the protocol must provide. It’s a way to achieve a form of multiple inheritance in Objective-C.
• In Objective-C, protocols are a way to declare a set of methods a class should implement. They define a blueprint for behavior without providing the actual implementation.
• A class can adopt (conform to) a protocol, thereby agreeing to implement its required methods. Protocols promote code consistency, allowing different classes to share a common interface and facilitating communication and interoperability in the Objective-C language.

10. What is the purpose of the ‘self’ keyword in Objective-C?

Ans:

• ‘self’ is a keyword that represents the instance of the class. It is commonly used to refer to the current object within a method. ‘self’ is used to access instance variables and invoke other methods on the same object. In Objective-C, the ‘self’ keyword refers to the current instance of the class.
• It is used to access and manipulate the instance variables and methods of the current object within its own implementation. ‘self’ is crucial for distinguishing between instance variables and parameters with the same name and invoking methods on the current object.

11. What is the role of the ‘super’ keyword in Objective-C?

Ans:

• The ‘super’ keyword is used to invoke a method from the superclass. It is often used in overridden methods to call the version of the method defined in the parent class. The ‘super’ keyword in Objective-C is used to refer to the superclass (parent class) of the current class.
• It allows access to methods and properties defined in the superclass, enabling a subclass to invoke and override methods from its parent class. ‘Super’ is often used when overriding methods in a subclass to call the superclass implementation before or after adding specific behavior in the subclass.

12. Explain the difference between synchronous and asynchronous tasks in Objective-C.

Ans:

Functional Components	Class Components
Created using ES6 arrow functions or regular JavaScript functions, making them concise and more readable.	Created using ES6 classes, involving a more verbose syntax with the use of the class keyword and lifecycle methods.
Cannot hold state or lifecycle methods before React 16.8; introduced Hooks, allowing functional components to manage state and lifecycle methods.	Can hold state and lifecycle methods inherently, making them suitable for more complex component logic and state management.
No lifecycle methods before React 16.8; Hooks introduced useEffect for handling side effects and component lifecycle events.	Utilizes traditional lifecycle methods such as componentDidMount, componentDidUpdate, and componentWillUnmount for handling component lifecycle events.

13. How do you handle exceptions in Objective-C?

Ans:

• Objective-C uses the @try, @catch, and @finally blocks for exception handling. Code that might raise an exception is placed within a @try block, and if an exception occurs, it can be caught and handled in the @catch block.
• It’s important to note that while exceptions can be caught and handled, it’s generally recommended to use error handling mechanisms (using NSError and returning error objects) for expected runtime errors, reserving exceptions for truly exceptional situations. Using exceptions for flow control is discouraged in Objective-C.

14. What is the role of the ‘copy’ attribute for property declarations?

Ans:

When using the ‘copy’ attribute for a property, the object is copied when set, ensuring that the property holds a distinct copy of the object. This is often used for mutable objects to prevent unintended modifications. In Objective-C, the ‘copy’ attribute for property declarations specifies that the object should be copied rather than retained when assigning a new value to the property. This is particularly useful when dealing with mutable objects, ensuring the property holds an independent copy of the assigned object.

15. What is the difference between ‘retain’, ‘assign’, and ‘strong’ in property attributes?

Ans:

• Retain Increases reference count in Objective-C for manual memory management.
• Assign: Used for non-object types, doesn’t affect reference count in Objective-C.
• Strong: Indicates ownership and increases reference count in Objective-C and Swift with Automatic Reference Counting (ARC).

16. Explain the concept of fast enumeration in Objective-C.

Ans:

Fast enumeration, introduced with Objective-C 2.0, provides a concise and efficient way to iterate through elements in a collection, such as NSArray or NSSet, using a for…in loop. The fast enumeration in Objective-C provides a convenient way to iterate over elements in a collection (like arrays) without index management. It’s achieved using the for…in the loop. Fast enumeration is more concise and less error-prone than traditional methods, making code cleaner and easier to read.

17. What is the purpose of the ‘instancetype’ keyword in Objective-C?

Ans:

• ‘instance type’ is a return type that indicates the type of the receiving instance in methods that create and return new instances. It improves type safety when working with factory methods.
• The instance type keyword in Objective-C is used as a return type in methods to indicate that the method returns an instance of the class for which it is implemented. It is a hint to the compiler that the method is expected to return an object of the receiver’s type.

18. What is the significance of the ‘pragma mark’ directive in Objective-C?

Ans:

‘pragma mark’ organizes and categorizes methods in Xcode’s symbol navigator. It helps developers structure and navigate through the code more efficiently. The #pragma mark directive in Objective-C organizes and categorizes methods or sections within the implementation file. It does not affect the compiled code but serves as a visual marker in Xcode’s code navigator, making it easier for developers to navigate and understand the structure of a class.

19. How does the ‘dispatch_async’ function work in Grand Central Dispatch (GCD)?

Ans:

• ‘dispatch_async’ is used to submit a code block for asynchronous execution on a dispatch queue.
• It helps parallelize tasks and improve application responsiveness.dispatch_async is a GCD function that queues a block for asynchronous execution on a specified queue.
• It doesn’t wait for the block to finish and allows the calling code to continue executing.

20. What is the purpose of the ‘NSCopying’ protocol in Objective-C?

Ans:

‘NSCopying’ is a protocol that declares a method for creating a copy of an object. Classes adopting this protocol provide a way to duplicate instances commonly used when dealing with mutable and immutable versions of objects. The ‘NSCopying’ protocol in Objective-C defines a method for creating a copy of an object. By adopting this protocol, a class ensures that instances of that class can be duplicated with a copy method, providing a mechanism for creating independent copies of objects. This is particularly useful in scenarios where you must create distinct copies of an object while preserving its state.

21. What is a selector in Objective-C?

Ans:

• A selector is a way to represent the name of a method in Objective-C. It acts as a unique identifier for a method and is often used when method names need to be dynamically determined or invoked.
•  In Objective-C, a selector is a way to represent the name of a method. It acts as a key that identifies a method at runtime. Selectors are often used with the message-passing syntax in Objective-C to invoke methods on objects. They are represented by the SEL type and are created using the @selector() directive.

22. Explain the difference between shallow copy and deep copy in Objective-C.

Ans:

Shallow copy creates a new object referencing the same underlying objects as the original. In contrast, deep copy creates a new object with copies of all the underlying objects. ‘copy’ in property attributes typically performs a shallow copy. In Objective-C, a shallow copy creates a new object with the same values as the original but does not duplicate the referenced objects within the original. If the original object references other objects, the shallow copy will share those references with the original.

23. How does the ‘IBOutlet’ keyword relate to Interface Builder in Objective-C?

Ans:

• ‘IBOutlet’ is a keyword used to declare a connection between a user interface element created in Interface Builder and the corresponding code in an Objective-C class. It is often used for connecting UI elements to instance variables. 
• In Objective-C, the IBOutlet keyword is used to declare a property as an outlet, which is a way to connect an interface element (like a button or label) in Interface Builder to your code. When you mark a property with IBOutlet, it tells Interface Builder that this property can be connected to a UI element in the storyboard or XIB file.

24. What is the purpose of the ‘NSNotificationCenter’ class in Objective-C?

Ans:

‘NSNotificationCenter’ facilitates communication between objects by allowing them to broadcast and listen for notifications. It’s commonly used for decoupling components in an application. The NSNotificationCenter class in Objective-C is used for broadcasting and receiving notifications within an application. It facilitates communication between different parts of the code without direct connections. Objects can register as observers to receive notifications and respond accordingly when a particular event occurs.

25. What are the key differences between ‘atomic’ and ‘nonatomic’ property attributes?

Ans:

• Atomic: Provides thread safety, ensuring only one thread can access the property.
• Nonatomic: Lacks inherent thread safety; multiple threads can access the property simultaneously.
• ‘atomic’ ensures that accessors for the property are thread-safe, while ‘nonatomic’ does not provide such guarantees. ‘nonatomic’ is generally preferred for performance reasons unless thread safety is explicitly required.

26. How is the swizzling method used in Objective-C?

Ans:

Identify the two methods you want to swap.

• Use runtime functions like method_exchangeImplementations to switch their implementations.
• This allows you to intercept or modify the behavior of a method dynamically.
• Method swizzling is a technique where the implementation of a method is replaced at runtime. It’s often used to modify the behavior of existing methods, especially in categories or dynamic runtime scenarios.

27. What is the purpose of the ‘dispatch_barrier_async’ function in Grand Central Dispatch?

Ans:

• The dispatch_barrier_async function in Grand Central Dispatch (GCD) is used to submit a block for asynchronous execution on a dispatch queue with a barrier.
• Synchronization: It ensures that the specified block is the only one executing on the target queue at any given time. While the barrier block executes, the queue is temporarily suspended for other blocks.

28. What is the ‘respondsToSelector’ method used for?

Ans:

‘respondsToSelector’ is a method that allows an object to check if another object can respond to a particular selector (method). It’s often used for dynamic method invocation and avoiding crashes when calling methods on objects that may not implement them. The respondsToSelector method is used in Objective-C to check if an object responds to a particular selector (method). It helps prevent crashes by allowing developers to determine whether an object supports a specific method before attempting to call it.

29. Explain the concept of blocks in Objective-C.

Ans:

• Blocks are a language feature introduced in Objective-C that allows the creation of self-contained code units. They are similar to Closures in other languages and are often used for asynchronous programming and passing functions as arguments.
• Blocks in Objective-C are language-level constructs that allow you to create and use anonymous functions or code snippets more concisely and flexibly. They are similar to C function pointers or closures in other programming languages.

30. What is the purpose of the ‘NSUserDefaults’ class in Objective-C?

Ans:

‘NSUserDefaults’ stores simple data types such as NSString, NSNumber, and NSData. It provides a convenient way to save and retrieve user preferences and settings. The NSUserDefaults class in Objective-C is used for simple data persistence, allowing you to store small amounts of data such as user preferences, settings, or application states between launches. It provides a convenient interface to interact with the user’s default database, making it easy to read and write key-value pairs.

31. Explain the concept of properties in Objective-C.

Ans:

Properties provide a way to encapsulate instance variables and define accessor methods. They simplify the syntax for getting and setting class values by automatically generating these methods. In Objective-C, properties provide a convenient way to declare and manage an object’s attributes (instance variables). They encapsulate the getter and setter methods for accessing and modifying these attributes. By using the @property declaration, you automatically generate the corresponding accessor methods.

32. What is the purpose of the ‘dispatch_group’ in Grand Central Dispatch?

Ans:

• ‘dispatch_group’ monitors the completion of a set of tasks. It allows you to wait for multiple asynchronous tasks to finish before proceeding with additional code.dispatch_group in Grand Central Dispatch (GCD) monitors the completion of a group of tasks.
•  It allows you to wait for multiple tasks to finish execution before moving on to your code’s next set of instructions. This is particularly useful when you have several asynchronous tasks and want to perform some action only when they are completed.

33. How does the ‘NSPredicate’ class work in Objective-C?

Ans:

‘NSPredicate’ is used to define conditions used to filter arrays or other collections. It allows you to create complex queries for data retrieval based on specific criteria.NSPredicate in Objective-C is a class that represents a query for filtering data. It’s commonly used with Core Data and NSArray to specify conditions that objects or elements must meet. You can create predicates with different operators, such as comparison operators, logical operators, and more.

34. Explain the concept of categories in Objective-C.

Ans:

• Categories allow you to add methods to existing classes without modifying their source code. They are useful for extending functionality and organizing code into logical units. In Objective-C, categories are a way to add methods to a class without subclassing it.
• They allow you to extend the functionality of existing classes, including system classes, without modifying their original implementation. This is particularly useful when you want to add methods to classes for which you don’t have access to the source code.

35. What is the purpose of the ‘NSFileManager’ class in Objective-C?

Ans:

‘NSFileManager’ provides an interface for interacting with the file system. It is used for creating, deleting, and managing files and directories. The NSFileManager class in Objective-C is part of the Foundation framework and provides an interface for working with the file system. It allows you to perform various file-related operations, such as creating, deleting, copying, moving, and querying files and directories.

36. How does the ‘copyWithZone’ method relate to object copying in Objective-C?

Ans:

• ‘copyWithZone’ is a method defined by the ‘NSCopying’ protocol. It is used to create a copy of an object, often used in conjunction with the ‘copy’ attribute for properties.
• In Objective-C, the copyWithZone method is part of the NSCopying protocol, and it is used to create a copy of an object.
• This method is responsible for performing a shallow copy of an object, meaning it duplicates the object itself but not the objects it references.
• The copyWithZone method is called when you send the copy message to an object.

37. Explain the concept of method chaining in Objective-C.

Ans:

• Method chaining involves invoking multiple methods on an object in a single line of code. It enhances code readability and conciseness, often used when performing a sequence of operations.
• Method chaining in Objective-C is a programming style where multiple method calls are chained together on the same object, allowing for concise and readable code. This is achieved by designing methods to return the object itself (or a new object), enabling the subsequent method calls to be invoked on the result of the previous one.

38. What is the purpose of the ‘dispatch_semaphore’ in Grand Central Dispatch?

Ans:

‘dispatch_semaphore’ controls access to a shared resource by limiting the number of tasks that can access it concurrently. It is often synchronized in multithreaded environments.dispatch_semaphore is part of Grand Central Dispatch (GCD) in Objective-C. It controls access to a resource in a concurrent programming environment. Semaphores are synchronization primitives that allow a certain number of threads to access a particular code block or resource simultaneously while limiting the total number of concurrent accesses.

39. How does the ‘NSOperationQueue class facilitate concurrent programming in Objective-C?

Ans:

• ‘NSOperationQueue’ is a high-level API that manages the execution of operations concurrently. It simplifies the coordination of tasks and provides a way to control the execution order. The NSOperationQueue class in Objective-C provides a high-level interface for managing and scheduling the execution of operations concurrently. 
• Operations are encapsulations of code that can be executed concurrently in a queue-based system. NSOperationQueue helps simplify the management of concurrent tasks and provides features like dependency management, priority settings, and cancellation.

40. Explain the purpose of the ‘Nib’ files in Objective-C development.

Ans:

Nib files (or XIB files) are Interface Builder files used to design and configure user interfaces visually. They store information about the layout and connections of UI elements in an application. Nib files, short for “NeXT Interface Builder” and also known as XIB files (XML Interface Builder), are a type of resource file in Objective-C development used to store graphical user interface (GUI) layouts and configurations. They play a crucial role in developing macOS and iOS applications, allowing developers to design interfaces visually using Interface Builder.

41. What is the difference between ‘retain cycle’ and ‘memory leak’ in Objective-C?

Ans:

A ‘retain cycle’ occurs when two or more objects hold strong references to each other, preventing them from being deallocated. A ‘memory leak’ happens when memory is allocated but not properly deallocated, gradually increasing memory usage. A retain cycle occurs when objects hold strong references to each other, preventing deallocation. A memory leak is any situation where unused memory is not released. Retain cycles can cause memory leaks, but not all memory leaks involve retain cycles.

42. How does the ‘copy’ attribute for property declarations behave with immutable and mutable objects?

Ans:

• For immutable objects, ‘copy’ ensures the property holds a distinct copy, preventing unintentional changes. For mutable objects, it’s a good practice to use ‘copy’ to avoid unexpected modifications by external entities. 
• The copy attribute in property declarations in Objective-C is typically used with objects that conform to the NSCopying protocol. When a property is declared with a copy, a copy of the object will be created when it is set rather than just taking the Reference.

43. Explain the purpose of the ‘NSNotificationQueue’ class in Objective-C.

Ans:

‘NSNotificationQueue’ is used to manage posting notifications to different threads or queues. It allows you to control when and where notifications are delivered, aiding in thread-safe communication. The NSNotificationQueue class in Objective-C is used to manage the posting of notifications to help control the order in which notifications are delivered. It allows you to queue notifications and control the order in which they are posted, ensuring that certain notifications are delivered in a specific sequence.

44. What is the swizzling method, and why should it be used cautiously?

Ans:

• Method swizzling involves dynamically changing the implementation of a method at runtime. It should be used cautiously because it can lead to unexpected behavior, especially when modifying the behavior of existing methods in a class.
•  Method swizzling in Objective-C involves dynamically exchanging the implementation of two methods at runtime. It’s a powerful technique used to modify or extend the behavior of existing classes. Developers might use it for debugging, profiling, or adding functionality.

45. How is the ‘NSJSONSerialization’ class used for JSON parsing in Objective-C?

Ans:

‘NSJSONSerialization’ is a class that provides methods for converting JSON data to Foundation objects and vice versa. It’s commonly used for parsing JSON responses from web services. In Objective-C, the NSJSONSerialization class is used for JSON parsing. You can convert JSON data into Foundation objects (NSDictionary, NSArray, NSString, NSNumber, etc.) and vice versa.

46. What is the purpose of the ‘NSCache’ class in Objective-C?

Ans:

‘NSCache’ is used for caching temporary data in memory. It automatically handles the eviction of objects when memory is low, making it suitable for managing a cache of data. The primary purpose of NSCache is to store transient, non-essential objects that can be discarded when the system is under memory pressure. It helps improve performance by allowing the system to manage the cache’s memory usage automatically. NSCache can automatically remove objects from the cache when memory is needed elsewhere to free up resources.

47. Explain the concept of method overriding in Objective-C.

Ans:

• Method overriding occurs when a subclass provides its implementation of a method that is already defined in its superclass. It allows the subclass to customize or extend the behavior of the inherited method. Method overriding in Objective-C allows a subclass to provide its implementation for a method already defined in its superclass.
• It enables the customization and extension of inherited methods by maintaining the same signature. The use of super allows calling the superclass version within the overridden method.

48. What is the difference between a shallow copy and a deep copy in Objective-C, and when might you prefer one?

Ans:

• Shallow Copy: Creates a new collection with references to the same objects. Changes affect both the original and the copy. Memory-efficient and faster.
• Deep Copy: Creates a new collection with duplicated objects. Changes in the copy don’t impact the original. Use when you need an independent copy or when dealing with mutable objects.

49. How is exception handling different in Objective-C compared to other programming languages?

Ans:

• Two Mechanisms: Objective-C uses @try-@catch blocks and NSException objects for exception handling.
• Not Common for Error Handling: Exceptions are less commonly used for routine error handling in Objective-C; error codes and NSError are preferred for expected errors.
• Historical Practices: Objective-C’s exception handling has historical roots, and modern codebases may rely more on error objects and return codes.
• Use of @finally: Objective-C supports @finally blocks for code that always executes, whether an exception was thrown.

50. Explain the purpose of the ‘UIResponder’ class in iOS development.

Ans:

‘UIResponder’ is a fundamental class in iOS development that forms the base for handling events and user interactions. It includes methods for responding to the application’s touch events, motion events, and other input events. In iOS development, the UIResponder class is fundamental within the UIKit framework. It is the base class for objects that can respond to and handle events such as user input (touches, gestures, etc.) and system events.

51. What is the ‘self’ parameter in Objective-C method declarations?

Ans:

• The ‘self’ parameter represents the class instance that is the method’s target. It allows methods to access the properties and other members of the instance.
• In Objective-C, the self parameter is an implicit parameter representing the instance of the class that is the message’s target. It is always the first parameter in a method declaration.

52. Explain the difference between ‘id’ and ‘instancetype’ in Objective-C.

Ans:

• Id: A generic object pointer used for method return types and parameters when the specific class type is unknown or ignored.
• Instance type: Represents the type of the receiver in method return types, commonly used in class initializers to ensure the correct type is returned. Enhances type safety.

53. What is the purpose of the ‘UIApplicationDelegate’ protocol in iOS development?

Ans:

The ‘UIApplicationDelegate’ protocol defines methods that allow an application to respond to key events in its lifecycle, such as launching, entering the background, and terminating. The UIApplicationDelegate protocol in iOS development defines a set of methods that allow an object to respond to important events in the lifecycle of an iOS application. Objects that conform to this protocol, typically the application’s delegate, can customize the application’s behavior and handle events such as app launch, termination, and transitioning between different states.

54. How is method swizzling utilized for method interception in Objective-C?

Ans:

• Choose the Methods to Swizzle: Identify the class and the two methods you want to exchange.
• Create Helper Methods: Implement the methods that will replace the original methods. These methods should contain the custom behavior you want to add or replace.
• Perform the Swizzle: Exchange the implementations of the two methods using the method_exchangeImplementations function from the Objective-C runtime.

55. What is the role of the ‘dispatch_after’ function in Grand Central Dispatch?

Ans:

‘dispatch_after’ executes a code block after a specified delay on a dispatch queue. It’s commonly used for scheduling tasks in the future. The dispatch_after function in Grand Central Dispatch (GCD) schedules a block for execution after a specified delay. It allows you to perform a task or execute code after a certain time, providing a convenient way to manage asynchronous operations.

56. Explain the concept of ‘NSRunLoop’ in Objective-C.

Ans:

• ‘NSRunLoop’ provides an infrastructure for managing input sources such as timers, ports, and custom input sources. 
• It is responsible for handling events and managing the execution of tasks on a thread. In Objective-C, NSRunLoop is a class that provides an event processing loop, allowing tasks to be scheduled and executed in a run loop.
•  A run loop is an event-processing loop that continually checks for incoming events or tasks and processes them. The NSRunLoop class is part of the Foundation framework.

57. What is Key-Value Observing (KVO) in Objective-C, and how is it implemented?

Ans:

KVO is a mechanism for observing changes in the properties of an object. It’s implemented by registering an observer for a key path, and the observer is notified when the value of the observed property changes. Key-value observing (KVO) is a mechanism in Objective-C that allows objects to be notified of changes to the properties of other objects. It enables one object to observe changes in the values of specific properties of another object and receive notifications when those values change.

58. How does the ‘atomic’ property attribute affect multithreading in Objective-C?

Ans:

• Atomic: Provides thread safety for property access by automatically adding locks. Slower due to locking mechanisms.
• Nonatomic: Does not guarantee thread safety. Faster, suitable when managing thread safety manually or when performance is a higher priority.

59. What is the purpose of the ‘__block’ specifier in Objective-C?

Ans:

• ‘__block’ is used when declaring variables within a block to indicate that the variable should be mutable inside the block, even if it is normally immutable outside the block.
• Purpose of __block:
• Without __block, variables declared within a block are treated as constants, and any attempt to modify them will result in a compilation error.
• Adding __block allows the variable to be mutable within the block, and changes made to it are visible outside the block.

60. Explain the concept of lazy loading in Objective-C.

Ans:

Lazy loading is a design pattern where an object is created or initialized only when needed, often used to improve performance and reduce memory usage by loading resources on demand. Lazy loading in Objective-C involves delaying the initialization of an object until it’s needed. This optimization is commonly used to improve performance and resource usage by avoiding unnecessary initialization of objects at the outset.

61. How does the ‘UIResponder’ chain work in iOS, and why is it important?

Ans:

The ‘UIResponder’ chain represents the hierarchy of objects that can respond to user events. Events are passed up the chain, allowing various objects to handle them, making it essential for user interaction in iOS.In iOS, the UIResponder chain is a hierarchical structure that allows objects to respond to and handle events. The UIResponder class provides the foundation for this chain, and it is essential for handling user interactions and managing the flow of events in an iOS application.

62. Explain the difference between ‘retain count’ and ‘strong reference’ in memory management.

Ans:

• Retain Count: retain Count counts how many times an object has been retained.
• They are used in manual memory management (pre-ARC).
• Developers explicitly manage the retain Count by calling retain, release, and autorelease.
• Strong Reference is an Automatic Reference Counting (ARC) ownership qualifier.
• It implies strong ownership of an object, preventing it from being deallocated as long as there is at least one strong Reference.
• Used in ARC, the system automatically retains counts based on strong references

63. What is the purpose of the ‘dispatch_barrier_sync’ function in Grand Central Dispatch?

Ans:

• ‘dispatch_barrier_sync’ is used to submit a block for execution on a dispatch queue with the guarantee that it will be the only block executing on that queue at a given time. It’s often used for synchronizing access to shared resources.
•  The dispatch_barrier_sync function in Grand Central Dispatch (GCD) is used to submit a block for synchronous execution on a dispatch queue with a barrier applied. The primary purpose of this function is to ensure exclusive access to a specific resource or section of code while still utilizing the concurrent nature of a dispatch queue.

64. How does the ‘NSPredicate’ differ from ‘NSComparisonPredicate’ in Objective-C?

Ans:

NSPredicate:

• Type: Abstract base class for representing conditions.
• Usage: Can represent various types of conditions, not limited to comparisons.
• Examples: Supports complex predicates, such as compound predicates, with logical operations (AND, OR, NOT).

65. What is the role of the ‘NSFileManagerDelegate’ protocol in Objective-C?

Ans:

• There is no NSFileManagerDelegate protocol in Objective-C as of my knowledge cutoff in January 2022. The NSFileManager class in Objective-C does not have a dedicated delegate protocol.
• NSFileManager is primarily responsible for managing files and directories, and it provides methods for performing operations like creating, copying, moving, and deleting files.

66. How is the ‘NSOperation’ class used for concurrent programming in Objective-C?

Ans:

‘NSOperation’ is an abstract class representing a single work unit. Subclasses can be used to encapsulate tasks, and instances can be added to an ‘NSOperationQueue’ for concurrent execution. The NSOperation class in Objective-C is part of the Foundation framework and provides a way to encapsulate units of work in a multithreaded environment. It performs concurrent or asynchronous tasks without dealing directly with threads. NSOperation is often used in conjunction with NSOperationQueue for managing and executing operations.

67. Explain the purpose of the ‘@autoreleasepool’ block in Objective-C.

Ans:

‘@autoreleasepool’ creates a scope in which temporary objects are automatically released. It helps manage memory efficiently, especially when many temporary objects are created. The @autoreleasepool block in Objective-C is used to manage the lifecycle of objects, particularly for memory management. It provides a way to allocate and deallocate objects within a specific scope efficiently, reducing memory usage and improving the performance of your application.

68. What is the ‘NSInvocation’ class, and how is it used in Objective-C?

Ans:

‘NSInvocation’ is a class that represents an encapsulation of a method invocation. It allows you to create, configure, and invoke methods at runtime dynamically. The NSInvocation class in Objective-C is part of the Foundation framework and represents an Objective-C message invocation. It allows you to encapsulate a method invocation, including the target object, the method to be called, and its arguments.

69. How are protocols different from interfaces in other programming languages?

Ans:

• It can include optional methods.
• Classes adopt protocols.
• Interfaces in Other Languages (e.g., Java, C#):
• Common in various languages.
• It can include methods, constants, and properties.
• Typically, all methods must be implemented.
• Classes implement interfaces.

70. What is the purpose of the ‘NSRunLoopCommonModes’ in iOS development?

Ans:

‘NSRunLoopCommonModes’ is a mode that includes a set of common modes used by run loops. It allows timers, sources, and observers to be added to multiple run loop modes simultaneously, improving flexibility.NSRunLoopCommonModes in iOS development represents a set of run loop modes commonly used to schedule tasks on a run loop. This constant ensures that certain tasks are executed when the run loop is in these common modes. It’s particularly useful for tasks that need to be performed during user interactions, such as updating the UI.

71. How does the ‘UIWebView’ differ from ‘WKWebView’ in iOS development?

Ans:

UIWebView:

• Older and deprecated.
• We have limited performance and features.
• Single-threaded JavaScript execution.

WKWebView:

• Modern and recommended.
• Better performance and JavaScript execution.
• Supports modern web standards.
• Nitro JavaScript engine for improved speed.

72. Explain the purpose of the ‘autorelease’ pool in manual memory management.

Ans:

The ‘autorelease’ pool is used in manual memory management to delay the release of objects until the pool is drained. It’s essential for managing memory efficiently, especially when creating and using temporary objects. In manual memory management in Objective-C, the autorelease pool manages the lifetime of autorelease objects. Autoreleased objects are objects scheduled to be released at some point in the future, typically at the end of the current run loop iteration. The @autoreleasepool block is a common construct used to define the scope of an autorelease pool.

73. What is the role of the ‘NSNotification’ class in the observer pattern in Objective-C?

Ans:

‘NSNotification’ represents a message broadcast by an object to other objects interested in receiving notifications. It facilitates communication between different parts of an application using the observer pattern. The NSNotification class in Objective-C is part of the Foundation framework and plays a central role in implementing the observer pattern. The observer pattern is a behavioral design pattern where an object (the subject) maintains a list of its dependents (observers) and notifies them of state changes, typically by calling one of their methods.

74. How does the ‘UIActivityIndicatorView’ class work in iOS, and when might you use it?

Ans:

UIActivityIndicatorView Works:

• Appearance: Circular spinner indicating ongoing activity.
• Initialization: We created it programmatically or in Interface Builder.
• Start/Stop Animation: startAnimating begins, stopAnimating halts animation.
• Visibility: They are shown/hidden with hidden property.
• Style and Color: Supports styles (small/large) and color customization

75. Explain the purpose of the ‘NSURLRequest’ and ‘NSURLSession’ classes in iOS networking.

Ans:

NSURLRequest:

• Purpose: Describes a URL load request.
• Usage: Configures details of an HTTP request (URL, method, headers).

NSURLSession:

• Purpose: High-level API for network tasks.
• Usage: Creates tasks for data retrieval, file downloads, or uploads.
• Features: Supports background sessions, various task types, and configuration options

76. What is the significance of ‘UIPickerView’ in iOS development?

Ans:

‘UIPickerView’ is a control allowing users to select from a list of multiple options. It is commonly used for presenting a set of choices, such as selecting a date or time. The UIPickerView in iOS development is a versatile user interface component that allows users to select from a list of options presented in a wheel or column-like fashion. It is commonly used for choosing dates, times, or other categorical data. The significance lies in providing an intuitive and interactive way for users to make selections, enhancing the overall user experience in iOS applications. Developers can customize the appearance and behavior of UIPickerView to suit the specific requirements of their app.

77. How does the ‘NSPredicateEditor’ class facilitate complex predicate creation in Objective-C?

Ans:

‘NSPredicateEditor’ is a UI component providing an interface for visually creating complex predicates. It allows users to build compound predicates using a graphical representation. The NSPredicateEditor class in Objective-C facilitates complex predicate creation by providing a visual interface for users to construct and edit compound predicates. It allows users to combine multiple conditions using logical operators (AND, OR) and compare them against various attributes.

78. What is the purpose of the ‘NSCacheDelegate’ protocol in Objective-C?

Ans:

• ‘NSCacheDelegate’ allows an object to respond to events related to an ‘NSCache’ instance, such as when objects are evicted from the cache. It provides opportunities for custom behavior when managing cached data. 
• The NSCacheDelegate protocol in Objective-C defines methods that provide additional control and customization for objects that act as delegates for an NSCache instance. An NSCache is a mechanism in iOS and macOS for temporarily storing and managing cached objects in memory.

79. Explain the concept of ‘forwarding’ in Objective-C messaging.

Ans:

Forwarding in Objective-C occurs when an object cannot respond to a received message. Instead of crashing, Objective-C provides mechanisms for forwarding the message to another object or handling it dynamically. In Objective-C messaging, “forwarding” refers to a mechanism where an object can dynamically redirect messages it receives to another object. This is particularly useful when an object doesn’t implement a specific method. Still, instead of crashing, Objective-C allows the object to forward the message to another object that can handle it.

80. How does the ‘UIViewController’ lifecycle work in iOS development?

Ans:

• Initialization: init methods are called.
• Loading View: loadView creates the view hierarchy.
• View Loading: viewDidLoad for one-time setup.
• View Will Appear : viewWillAppear before appearing.
• View Did Appear: viewDidAppear after appearing.
• View Will Disappear: The view will disappear before disappearing.
• View Did Disappear: viewDidDisappear after disappearing.
• Memory Warning: didReceiveMemoryWarning for low memory.

81. Explain the purpose of the ‘CGContext’ in Core Graphics in Objective-C.

Ans:

• Drawing Operations: Performs drawing operations like paths, shapes, images, and text.
• Coordinate System Management: Defines and manages the coordinate system for drawing.
• Graphics State Management: Maintains attributes like colour, line width, and font.
• Clipping Paths: Supports creating clipping paths for focused drawing areas.
• Coordinate Transformation: Allows precise control over the position and scaling of graphics elements.

82. What is the ‘NSCoder’ protocol in Objective-C?

Ans:

‘NSCoder’ is a protocol used for encoding and decoding objects. It is utilized in archiving (saving) and unarchiving (loading) objects to and from a file or data representation. The NSCoder protocol in Objective-C is a fundamental part of the Cocoa archiving system, used for encoding (archiving) and decoding (unarchiving) objects. It provides a way to convert objects and their properties into a stream of data (encoding) and reconstruct them from that data (decoding).

83. How does the ‘UIBezierPath’ class facilitate drawing custom shapes and paths in iOS development?

Ans:

• Path Creation: Defines paths using points, curves, and lines.
• Line and Curve Drawing: Supports straight lines, quadratic, and cubic Bezier curves.
• Closed Shapes: It easily closes paths for creating filled shapes.
• Stroke and Fill: Stroke paths with specified color and width, and fill paths with a fill color.

84. Explain the concept of the swizzling method and its use cases in Objective-C runtime.

Ans:

• Concept: Dynamically swapping the implementations of two methods at runtime.
• Method Modification: Change the behavior of existing methods dynamically.
• Debugging: Log or profile method calls for debugging purposes.
• Category Enhancements:Add methods to existing classes using categories.
• Dynamic Patching:Patch or fix issues in closed-source libraries.
• Aspect-Oriented Programming (AOP): Inject cross-cutting concerns like logging or security into multiple methods.
• Caution: Use the swizzling method carefully to avoid unexpected behavior or conflicts, especially in large codebases.

85. What is the purpose of the ‘dispatch_group_notify’ function in Grand Central Dispatch?

Ans:

• Purpose: Schedules a block to run when all tasks in a dispatch group have been completed.
• Usage: Used with dispatch_group_enter and dispatch_group_leave to track completion of asynchronous tasks.
• Example: Execute additional tasks or handle completion once all group-associated tasks are finished.

86. Explain the purpose of the ‘UIStackView’ class in iOS development.

Ans:

‘UIStackView’ is a container view in UIKit that simplifies the layout of a group of views. It automatically manages the arrangement and spacing of its subviews, making it easier to create dynamic and responsive layouts. The UIStackView class in iOS development is a container view that simplifies the layout and management of a group of arranged subviews. Its primary purpose is to provide an easy and efficient way to create complex user interfaces by organizing and aligning views in a stack horizontally or vertically.

87. How does the ‘atomic’ property attribute impact performance?

Ans:

• Impact on Performance: Introduces performance overhead due to internal locking.
• Considerations: It is useful for thread safety but less performant than nonatomic.
• Recommendation: Choose based on the balance between thread safety and performance needs. If performance is critical, consider nonatomic with external synchronization.

88. What is the role of the ‘NSOperationDependency’ in managing dependencies between operations in Objective-C?

Ans:

‘NSOperationDependency’ is used to establish dependencies between ‘NSOperation’ objects. It ensures that certain operations are executed only after their dependent operations have finished. In Objective-C, NSOperationDependency is not a specific class. However, you might be referring to NSOperation and its dependency management. In operations, dependencies are established using the dependency method of the NSOperation class.

89. What are the advantages of using protocols over inheritance in Objective-C?

Ans:

• Multiple Inheritance: Supports multiple protocols, overcoming the single-inheritance limitation.
• Avoids Deep Class Hierarchies: Promotes a more modular and maintainable code structure.
• Loose Coupling: Allows classes to conform without tight dependencies.
• Enhanced Code Reusability: Facilitates code reuse across unrelated classes.
• Better Support for Composition: Supports flexible and modular design through composition.
• Dynamic Behavior with Categories: Permits dynamic adoption of protocols using categories.

90. How does the ‘NSDecimalNumber’ class differ from ‘NSNumber’ in Objective-C?

Ans:

‘NSDecimalNumber’ is a subclass of ‘NSNumber’ specifically designed for handling decimal numbers with precise arithmetic. It is suitable for financial calculations and situations where accuracy is crucial.NSDecimalNumber is designed for precise decimal arithmetic, is suitable for financial calculations, and avoids rounding errors. NSNumber is a general-purpose class for representing numbers using basic C types, lacking the precision of NSDecimalNumber.

91. What is Key-Value Coding (KVC) in Objective-C, and how is it used?

Ans:

Key-value coding is a mechanism that allows accessing an object’s properties using string-based keys. It simplifies code by enabling dynamic property access and manipulation. Key-value coding (KVC) in Objective-C allows indirect access to an object’s properties through string-based keys. It enables you to get or set property values using strings, providing a flexible way to interact with objects.

92. Explain the purpose of the ‘UIPageViewController’ class in iOS development.

Ans:

• ‘UIPageViewController’ is a container view controller that manages a collection of view controllers as pages. It is often used for implementing page-based navigation, such as in a book or photo viewer.
• The UIPageViewController class in iOS development is designed to manage a collection of view controllers in a way that facilitates navigation through a series of content pages, often presented in a paged manner.
• Its primary purpose is to create an interactive, swipe-based navigation experience, commonly used in apps that display content in a book-like or carousel-style format.

93. How are property observers used in Objective-C?

Ans:

Property observers, like willSet and didSet, allow you to observe and respond to changes in property values. They are implemented in Objective-C by overriding setter methods or using the willChangeValueForKey and didChangeValueForKey methods. In Objective-C, property observers commonly associated with Swift properties don’t have a direct equivalent. However, you can achieve similar functionality using Key-Value Observing (KVO) to observe changes to an object’s properties.

94. What is the ‘UIApplication’ class in iOS, and how is it used to handle application-level events?

Ans:

UIApplication is a key class in iOS managing application-level events. Used for:

• Launch Control: Handles app launch events.
• Background Execution: Manages tasks running in the background.
• State Transitions: Notifies about state changes (background/foreground).
• URL Schemes: Allows responding to custom URL schemes.
• Remote Notifications: Handles incoming push notifications.
• Badge Management: Provides methods for managing app icon badges.
• Developers subclass UIApplication to customize behavior for specific events.

95. Explain the purpose of the ‘UIPanGestureRecognizer’ in iOS development.

Ans:

‘UIPanGestureRecognizer’ is a gesture recognizer class used to detect and handle panning (dragging) gestures. It is often used for implementing draggable views or interactive transitions.UIPanGestureRecognizer in iOS recognizes and handles panning gestures, allowing drag-and-drop functionality, custom gestures, interactive transitions, and manipulation of UI elements based on the user’s touch movement.