Top 30 Objective-C Interview Questions and Answers (2026)
Benjamin Walker
Preparing for an Objective-C role means anticipating what interviewers probe beyond syntax and memory models. An Objective-C interview exposes reasoning depth, design judgment, and practical understanding through targeted questions consistently.
These questions open paths for freshers, mid-level engineers, and seniors, reflecting industry trends and real delivery. Employers value technical expertise, analysis, and problem framing from professionals with hands-on experience, collaborating with team leaders and managers to apply Objective-C skills in production environments. This perspective supports growth across varied career stages. Read more…
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Top Objective-C Interview Questions and Answers
1) What is Objective-C and why is it used?
Objective-C is a strict superset of the C programming language that adds object-oriented capabilities and a dynamic runtime. It was originally developed in the early 1980s and is the primary language used for macOS and iOS app development before Swift. It inherits syntax from C but uses Smalltalk-style messaging for objects, which allows calling methods dynamically at runtime.
Objective-C is used for developing native apps on Apple platforms because it integrates tightly with Apple frameworks like Foundation and Cocoa/Cocoa Touch. This allows developers to build applications with full access to system APIs and rich UI components.
Example:
#import <Foundation/Foundation.h>
@interface Sample : NSObject
- (void)showMessage;
@end
@implementation Sample
- (void)showMessage {
NSLog(@"Hello from Objective-C!");
}
@end
int main() {
Sample *obj = [[Sample alloc] init];
[obj showMessage];
return 0;
}
2) Explain the basic structure of an Objective-C program.
An Objective-C program typically consists of:
- Preprocessor commands (such as
#import) - Interface (
@interface) – defines the class and its public methods/properties - Implementation (
@implementation) – contains method definitions - Methods – functions associated with objects
- Variables and Expressions & Statements – code logic
- Comments to describe code logic
This structure separates interface from implementation clearly, helping modularize code.
3) What are protocols in Objective-C and what types exist?
In Objective-C, a protocol is similar to an interface in other languages. It defines a set of methods that any class can adopt and implement, enabling multiple inheritance of method signatures (not implementation).
There are two types:
- Formal Protocols – Declared using
@protocol; can define required and optional methods. - Informal Protocols – Typically implemented as categories on
NSObject; optional by design.
Use Case: Delegation patterns in UIKit often use protocols (e.g., UITableViewDelegate).
4) What is the difference between #import and #include?
#includeis the C preprocessor directive that inserts the contents of one file into another, which can cause multiple inclusion problems.#importis an Objective-C directive that ensures a file is only included once, avoiding duplication.
Thus, #import is safer and preferred in Objective-C development.
5) What is the use of categories in Objective-C?
Categories extend an existing class by adding methods without subclassing or modifying original code. They allow you to logically separate methods into groups or add extra behavior to framework classes like NSString.
Example Use: Adding utility methods to NSArray without subclassing:
@interface NSArray (Utility) - (NSArray *)reversedArray; @end
6) What does @synthesize do?
The @synthesize directive tells the compiler to generate getter and setter methods for a property declared with @property. This enforces encapsulation and automates boilerplate code.
Since Xcode 4.4, auto-synthesis is default — you often do not need to write @synthesize explicitly.
7) Explain memory management in Objective-C.
Objective-C uses Automatic Reference Counting (ARC) to manage memory. ARC adds compiler-generated retain/release calls that ensure objects stay alive as long as needed and are deallocated when no references remain.
Key concepts:
- Strong references keep objects alive
- Weak references do not retain objects, avoiding retain cycles
Example:
@property (strong, nonatomic) NSString *name; @property (weak, nonatomic) id delegate;
8) What is the difference between NSArray and NSMutableArray?
- NSArray: Immutable array — contents cannot change after creation.
- NSMutableArray: Mutable array — allows adding, removing, or replacing elements.
Example:
NSMutableArray *list = [NSMutableArray arrayWithObjects:@"A", @"B", nil]; [list addObject:@"C"]; // Allowed
9) What is data encapsulation in Objective-C?
Data encapsulation binds data and the functions that operate on it into a single unit (class) while restricting direct access from outside the class. This enforces modularity, data protection, and abstraction.
10) How does method calling work in Objective-C?
Objective-C uses message passing syntax:
[object methodName];
Here, object receives a message to invoke methodName. If the method is not resolved, the runtime handles forwarding or throws an exception. This flexibility is a powerful feature of Objective-C’s dynamic runtime.
11) Explain the difference between strong, weak, assign, and copy properties in Objective-C.
Objective-C properties define how memory is managed for object references, and choosing the correct attribute is critical for application stability. The strong attribute increases the reference count of an object, ensuring it remains in memory as long as the property exists. It is commonly used for ownership relationships. The weak attribute does not retain the object, automatically setting the reference to nil when the object is deallocated, which helps prevent retain cycles, especially in delegate patterns.
The assign attribute is used for primitive data types such as integers and floats. It does not retain objects and should not be used for Objective-C objects under ARC. The copy attribute creates a copy of the assigned object, which is particularly important for mutable objects like NSMutableString to prevent unintended modification.
| Attribute | Retains Object | Use Case |
|---|---|---|
| strong | Yes | Ownership |
| weak | No | Delegates |
| assign | No | Primitives |
| copy | Copies | Immutable safety |
12) How does Automatic Reference Counting (ARC) work internally?
Automatic Reference Counting (ARC) is a compile-time memory management system that inserts retain, release, and autorelease calls automatically. Unlike garbage collection, ARC does not run at runtime; instead, the compiler analyzes object lifecycles and determines where memory management calls are necessary. This ensures efficient memory usage without developer intervention.
ARC tracks strong references to objects and deallocates them when no strong references remain. Weak references are automatically zeroed out when the object is deallocated, improving application safety. ARC does not manage Core Foundation objects automatically, so bridging techniques such as __bridge and __bridge_transfer are required.
For example, retain cycles can still occur if two objects strongly reference each other, which must be resolved using weak references.
13) What is the Objective-C runtime, and why is it important?
The Objective-C runtime is a powerful system that enables dynamic behavior in Objective-C programs. It allows methods to be resolved at runtime rather than compile time, enabling features such as dynamic method dispatch, message forwarding, and introspection.
This runtime enables Objective-C to determine which method to call only when a message is sent. If the method does not exist, the runtime provides multiple opportunities to handle it, such as forwarding the message to another object. This makes Objective-C highly flexible and extensible.
Runtime functions also allow developers to inspect class hierarchies, add methods dynamically, and swizzle method implementations, which is commonly used in debugging and analytics frameworks.
14) What are blocks in Objective-C, and what are their benefits?
Blocks in Objective-C are closures that encapsulate code and variables for later execution. They are similar to lambda expressions in other programming languages and are commonly used for callbacks, asynchronous execution, and enumeration.
Blocks capture variables from their surrounding scope, which can be modified using the __block keyword. They simplify code readability and reduce the need for delegate patterns in many scenarios.
Benefits of blocks include improved code locality, better readability, and ease of asynchronous programming. However, developers must be cautious of retain cycles when blocks strongly capture self. Using __weak references inside blocks prevents memory leaks.
15) What is the difference between nil and NULL in Objective-C?
In Objective-C, nil represents a null object pointer, while NULL represents a null pointer for C types. Although they often evaluate to the same value (zero), they are semantically different and should be used appropriately.
nil is used for Objective-C objects and allows messages to be sent safely without crashing the application. When a message is sent to nil, it simply returns zero or nil. In contrast, dereferencing a NULL pointer in C results in undefined behavior and often crashes the application.
Using nil improves code safety and readability when dealing with Objective-C objects, while NULL should be reserved for C structures and pointers.
16) Explain delegation in Objective-C with an example.
Delegation is a design pattern in Objective-C that allows one object to communicate events or decisions to another object. It is implemented using protocols and weak references to avoid retain cycles. Delegation promotes loose coupling and reusability.
A delegating object defines a protocol, and the delegate object adopts and implements that protocol. The delegating object then calls methods on its delegate when certain events occur.
For example, a table view notifies its delegate when a row is selected. This design allows behavior to be customized without subclassing and is widely used throughout Apple frameworks.
17) What are categories versus extensions in Objective-C?
Categories and extensions both allow developers to add functionality to existing classes, but they serve different purposes. Categories add public methods to a class and are often used to organize code or add utility methods. Extensions, also known as class extensions, are typically declared in implementation files and allow adding private properties and methods.
Categories cannot add instance variables, while extensions can. Categories are often used to enhance framework classes, whereas extensions are used for encapsulation and internal implementation details.
Understanding the difference ensures better class design and improved maintainability.
18) How does KVC (Key-Value Coding) work in Objective-C?
Key-Value Coding (KVC) allows indirect access to an object’s properties using string keys. It enables setting and retrieving values dynamically without explicitly calling getter or setter methods.
KVC is widely used in Cocoa bindings and serialization frameworks. It relies on a well-defined lookup pattern to resolve keys and supports collection operators for working with arrays and sets.
For example, valueForKey: retrieves a value dynamically, while setValue:forKey: assigns a value. Incorrect key usage may result in runtime exceptions, so careful validation is required.
19) What is KVO (Key-Value Observing), and how is it different from notifications?
Key-Value Observing (KVO) allows objects to observe changes to specific properties of another object. It is tightly coupled to KVC and enables automatic notifications when a property value changes.
Unlike notifications, KVO is fine-grained and property-specific, while notifications are broadcast-based. KVO requires proper observer removal to avoid crashes, whereas notifications are more loosely coupled.
KVO is ideal for observing model changes in MVC architecture, while notifications are better suited for system-wide events.
20) What are the advantages and disadvantages of using Objective-C today?
Objective-C offers dynamic runtime features, mature tooling, and deep integration with legacy Apple frameworks. It allows flexible message handling and is still widely used in large, mature codebases.
However, Objective-C has verbose syntax, a steeper learning curve, and has largely been replaced by Swift for new development. Swift provides improved safety, readability, and performance optimizations.
| Aspect | Advantages | Disadvantages |
|---|---|---|
| Runtime | Dynamic | Complex |
| Syntax | Powerful | Verbose |
| Ecosystem | Mature | Declining adoption |
21) Explain the Objective-C class lifecycle from allocation to deallocation.
The lifecycle of an Objective-C object begins with memory allocation and ends with deallocation. This lifecycle is managed primarily through ARC or manual reference counting in legacy systems. The process starts with alloc, which allocates memory for the object and initializes its instance variables to default values. This is followed by init, which prepares the object for use by setting initial state.
Once initialized, the object remains alive as long as at least one strong reference exists. During its lifetime, the object may receive messages, participate in delegation, and interact with other objects. When all strong references are released, ARC automatically invokes dealloc, where cleanup tasks such as removing observers or freeing resources are performed.
Understanding this lifecycle is essential for avoiding memory leaks, dangling pointers, and improper resource handling.
22) How does message forwarding work in Objective-C?
Message forwarding is a multi-step mechanism used when an object receives a message it cannot handle. Instead of immediately crashing, Objective-C provides several opportunities to dynamically resolve the method. First, the runtime checks +resolveInstanceMethod: to see if the method can be added dynamically. If not resolved, it proceeds to -forwardingTargetForSelector: to redirect the message to another object.
If that fails, the runtime invokes -methodSignatureForSelector: and -forwardInvocation: to manually forward the message. This enables proxy objects, decorators, and dynamic behaviors.
This mechanism highlights the flexibility of Objective-C and is commonly used in frameworks such as NSProxy and mocking libraries.
23) What are retain cycles, and how do you prevent them?
A retain cycle occurs when two or more objects hold strong references to each other, preventing ARC from deallocating them. This results in memory leaks, even though the objects are no longer needed. Retain cycles commonly occur between parent and child objects, delegates, and blocks capturing self.
To prevent retain cycles, developers use weak references for non-ownership relationships, such as delegates. In blocks, __weak or __unsafe_unretained references to self are used to avoid strong capture.
Identifying retain cycles using Instruments and carefully designing ownership semantics are critical skills for Objective-C developers working on long-running applications.
24) How does Objective-C handle concurrency and multithreading?
Objective-C provides multiple mechanisms for concurrency, with Grand Central Dispatch (GCD) being the most widely used. GCD allows developers to submit tasks to queues that execute either serially or concurrently. It abstracts thread management, improving performance and safety.
Other concurrency tools include NSThread, NSOperation, and NSOperationQueue. While NSThread offers low-level control, NSOperationQueue provides dependency management, cancellation, and priority handling.
GCD is generally preferred for performance-critical code, while NSOperationQueue is suitable for complex workflows requiring fine-grained control.
25) What is method swizzling, and when should it be used?
Method swizzling is a runtime technique that allows developers to exchange the implementations of two methods. This is achieved using Objective-C runtime APIs and enables modification of behavior without subclassing or modifying original source code.
Swizzling is commonly used in analytics, logging, debugging, and testing frameworks. However, it should be used with caution because it can introduce unexpected behavior, make debugging difficult, and break functionality if underlying implementations change.
In production code, method swizzling should be carefully documented and limited to well-defined use cases to maintain code stability.
26) Explain the difference between shallow copy and deep copy in Objective-C.
A shallow copy duplicates the container object but not the objects it contains. Both the original and copied containers reference the same underlying objects. In contrast, a deep copy duplicates both the container and all nested objects, creating independent copies.
Objective-C collection classes typically perform shallow copies by default. Deep copying requires explicit implementation, often using NSCopying or manual iteration.
| Copy Type | Container Copied | Elements Copied |
|---|---|---|
| Shallow | Yes | No |
| Deep | Yes | Yes |
Understanding this difference is essential when working with mutable data structures to avoid unintended side effects.
27) How does Objective-C support introspection?
Introspection in Objective-C allows objects to examine their own structure and behavior at runtime. This includes checking class membership, method availability, and protocol conformance. Methods such as isKindOfClass:, respondsToSelector:, and conformsToProtocol: are commonly used.
Introspection enables defensive programming and dynamic behavior adaptation. For example, an object can check whether another object implements a method before calling it, improving runtime safety.
This capability is especially useful in loosely coupled systems and plugin-based architectures.
28) What is the difference between isEqual: and == in Objective-C?
The == operator compares memory addresses, determining whether two references point to the same object. The isEqual: method compares the content or logical equality of objects.
For example, two different string objects with the same text content may return NO when compared using ==, but YES when compared using isEqual:. Many Foundation classes override isEqual: to provide meaningful equality comparisons.
Choosing the correct comparison method is essential to avoid logical errors, especially when working with collections like sets and dictionaries.
29) How does Objective-C integrate with C and C++ code?
Objective-C is fully compatible with C and can interoperate with C++ through Objective-C++. By using .mm files, developers can mix Objective-C and C++ code within the same source file.
This integration allows reuse of existing C and C++ libraries while benefiting from Objective-C’s object-oriented features. Developers must manage name mangling and object lifecycles carefully to avoid memory and compatibility issues.
Objective-C++ is commonly used in performance-critical applications such as game engines and multimedia processing.
30) When should you choose Objective-C over Swift in modern development?
Objective-C is still a valid choice when maintaining large legacy codebases, integrating with older frameworks, or requiring advanced runtime features not easily achievable in Swift. Its dynamic messaging system and mature tooling make it suitable for certain low-level or framework-oriented development tasks.
However, for new projects, Swift is generally preferred due to improved safety, readability, and performance. The decision should be based on project requirements, team expertise, and long-term maintainability.
A strong understanding of Objective-C remains valuable, especially in enterprises with extensive existing Objective-C applications.
🔍 Top Objective-C Interview Questions with Real-World Scenarios & Strategic Responses
1) What are the key differences between Objective-C and Swift, and when would you still choose Objective-C?
Expected from candidate: The interviewer wants to assess your understanding of the language ecosystem and your ability to make informed architectural decisions.
Example answer: Objective-C is a dynamic, message-based language with strong runtime capabilities, while Swift emphasizes safety, performance, and modern syntax. I would still choose Objective-C when maintaining or extending large legacy iOS or macOS codebases where rewriting in Swift would introduce unnecessary risk or cost.
2) How does memory management work in Objective-C under ARC?
Expected from candidate: The interviewer is testing your understanding of memory management fundamentals and how ARC simplifies them.
Example answer: Under ARC, the compiler automatically inserts retain and release calls at compile time. Developers still need to avoid strong reference cycles by using weak or assign references appropriately, especially in delegate patterns and block usage.
3) Can you explain the difference between strong, weak, and assign properties?
Expected from candidate: The interviewer wants to ensure you understand object ownership and lifecycle management.
Example answer: Strong properties increase the retain count and keep an object alive. Weak properties do not retain the object and are set to nil when the object is deallocated. Assign is typically used for primitive types and does not manage object ownership.
4) Describe a time you debugged a difficult crash in an Objective-C application.
Expected from candidate: The interviewer is evaluating your problem-solving approach and debugging skills.
Example answer: In my previous role, I debugged a recurring crash caused by over-released objects in a multithreaded environment. I used Instruments with Zombies enabled to trace the deallocation and identified an incorrect property attribute, which resolved the issue once corrected.
5) How do categories differ from subclasses in Objective-C?
Expected from candidate: The interviewer wants to assess your understanding of code organization and extensibility.
Example answer: Categories allow adding methods to an existing class without subclassing, which is useful for modularizing functionality. Subclasses create new class hierarchies and can override behavior, but they increase coupling and complexity.
6) What are blocks in Objective-C, and how are they commonly used?
Expected from candidate: The interviewer is checking your familiarity with modern Objective-C patterns.
Example answer: Blocks are closures that encapsulate code and captured variables. They are commonly used for asynchronous callbacks, completion handlers, and enumeration. Care must be taken to avoid retain cycles by using weak references to self.
7) How would you handle threading and concurrency in Objective-C?
Expected from candidate: The interviewer wants to know how you ensure performance and responsiveness.
Example answer: At a previous position, I relied heavily on Grand Central Dispatch to manage background tasks and UI updates. I used serial queues for data consistency and concurrent queues for performance-critical operations.
8) Explain the delegate pattern and its advantages.
Expected from candidate: The interviewer is testing your understanding of common design patterns in iOS development.
Example answer: The delegate pattern allows one object to communicate events or data back to another without tight coupling. It promotes separation of concerns and makes code easier to test and maintain.
9) Describe how you would refactor a large, legacy Objective-C codebase.
Expected from candidate: The interviewer is evaluating your strategic thinking and experience with legacy systems.
Example answer: In my last role, I approached refactoring incrementally by adding unit tests first, isolating critical components, and improving code readability. I avoided large rewrites and focused on reducing technical debt safely over time.
10) How do you ensure code quality and maintainability in Objective-C projects?
Expected from candidate: The interviewer wants insight into your engineering discipline and teamwork.
Example answer: At my previous job, I emphasized consistent coding standards, thorough code reviews, and documentation. I also encouraged writing reusable components and using static analysis tools to catch issues early.
