9 Objective-C Interview Questions and Sample Answers

Updated 13 March 2023

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Objective-C is a programming language that computer scientists and other information technology professionals use to develop various frameworks. When you are applying for one of these positions, a hiring manager may ask you questions about Objective-C to assess your knowledge. Understanding how to answer interview questions about Objective-C can help you prepare for an interview for a job position that requires familiarity with this programming language.

In this article, we provide nine Objective-C interview questions and sample answers that you can study to create your own responses and improve your chances of getting a job offer.

9 Objective-C Interview Questions

Here are nine Objective-C interview questions with sample answers:

1. How do you control memory in Objective-C?

When a hiring manager asks this question, they may want to know that you are aware that memory allocation in Objective-C occurs dynamically. In your answer, explain that memory allocation occurs during a program's runtime. You may also provide the two ways of allocating memory in Objective-C.

Example: 'When working with Objective-C, memory allocation occurs dynamically. Memory allocation can occur during any program's runtime. The objects take up memory when the system is using them, and the system frees the objects when it no longer needs them to minimise the amount of memory that is in use. One way to allocate memory in Objective-C is manual retain-release (MRR). The other way to allocate memory in this programming language is via automatic reference counting (ARC).'

2. What are some potential drawbacks to memory management in Objective-C?

A hiring manager may ask this question to learn if you understand the challenges that memory management within Objective-C can present. Your response may indicate that you are aware of these potential challenges and know how to overcome them in your work. In your answer, you can discuss the results of over-freeing and under-freeing.

Example: 'There are two main potential drawbacks to memory management in Objective-C. The first is over-freeing, which can result in multiple system crashes. When under-freeing occurs in Objective-C, the system may produce memory leaks. These memory leaks can lead to a greater memory footprint within the application, which means that the program references a greater amount of memory when it is running.'

3. What is retain count in Objective-C?

The answer you provide to this question can show a hiring manager that you are aware of what occurs when a programmer sends objects via Objective-C. In your answer, define the default retain count. You can also explain what happens when you send an object as a retain message versus as a release message.

Example: 'In Objective-C, programmers implement the blueprint of ownership via reference counting. The retain count is what programmers calculate after the execution of the retain method. Every object present in Objective-C has a retain count. When a programmer creates a new object, the object automatically has a retain count of one. When a programmer sends a new object as a retain message, the object's count increases by one. Conversely, when a programmer sends a new object as a release message, the object's count decreases by one. An object undergoes deallocation when it retains count becomes zero.'

4. What are declared properties in Objective-C?

A hiring manager may ask this to determine how well you understand objects in terms of their relationships and attributes. In your answer, provide a brief definition of declared properties. You can also discuss the features that declared properties have to address the issues that accessor methods may cause.

Example: 'Declared properties dictate how accessor methods behave. They can synthesise various accessor methods depending on the specifications you outline. You may represent these properties syntactically so that the system's compiler can locate the implementation of any undeclared properties. In code, each property begins with the syntax "@property." Within the property, you may add optional attributes, including "read-only," "copy," "retain," "assign" and "read-write."'

5. Define the characteristics of a category in Objective-C.

The answer you provide to this question can show your understanding of a category's importance as it relates to a class in Objective-C. In your answer, explain that any class must have a category declaration. You may also show advanced knowledge by discussing the subclass as it relates to the category.

Example: 'Any class in Objective-C has a category declaration despite the lack of original source code that is available for utilisation. All of the methods that a user defines within a specific category are available for all cases to the class where it exists. It is also possible to use the category within the original class' subclass. This would operate similarly to an inheritance. There are no variations in the method a category creates. After the original class applies a category, the system can use the category at its runtime.'

6. When is it appropriate to use the NSArray object versus the NSMutableArray object?

A hiring manager may ask this question to gauge your understanding of these two objects that sound similar but have different functions. In your response, explain when you would use each one. Consider providing examples to clarify your explanations.

Example: 'You can execute NSArray when you have data that remains the same for a long period. For example, you can input a company name in this field, as it is likely to remain the same for a long time. By using NSArray, you can prevent other users from manipulating this element. Alternatively, you can execute NSMutableArray for data that is subject to change. For example, you may use the NSMutableArray object to record a function that has values transmitted to an array. The function can add elements as necessary, as a function yields different results over time.'

7. What are the methods for implementing the NSURL connection?

The NSURL connection is useful for loading URL requests synchronously and asynchronously, so a hiring manager may want to assess your familiarity with them. In your response, you can state that one of the primary methods for doing this is implementing a connection that received the response. You may also name a few other methods to enhance your answer.

Example: 'One of the primary methods is implementing a connection that receives the response from the system. You can also use the implementation of a connection that failed with an error. Still, you can implement a connection that receives data from the system but not necessarily the final response.'

8. What are blocks in Objective-C?

A hiring manager may ask this question to see if you know how to define one unit of behaviour without needing to create a whole Objective-C class. In your answer, define what a block is. Offer some details about the syntax that you use to create blocks in Objective-C.

Example: 'Blocks are elements that you can use to define one task without the need to create a whole Objective-C class. Essentially, blocks are still Objective-C objects but on a smaller scale. These features allow for the support of programming techniques like closures and lambdas within Objective-C. As you write the syntax for blocks, you can alter the signature to include any desired data.'

9. What are the two primary types of protocols in Objective-C?

This question can help a hiring manager gauge how well you understand the methods that Objective-C implements for particular use cases. In your answer, state that the two types of protocols in this programming language are formal and informal protocols. You can also describe how formal protocols are extensions of this programming language rather than original inclusions.

Example: 'An informal protocol is a category that you can locate on NSObject. Implicitly, it turns all of the present objects into adopters of the protocol. The informal protocol was a part of the original Objective-C language. Formal protocols proclaim a group of methods that client classes need to implement. All formal protocols have their own type-checking syntax, adoption and declaration. They were not a part of the original Objective-C language.'