CodeSubmit Interview Series

The 9 Best Objective-C Interview Questions in 2023

Looking for an Objective-C developer? Then, you need the right Objective-C interview questions. Here are the questions to ask at your next interview. 

Interviewing Objective-C developers 

Objective-C is a general-purpose, objective-oriented programming language. It was the standard programming language used by Apple for developing macOS and iOS applications until Swift was introduced in 2014. 

But how do you identify the best Objective-C developers? 

Here’s what you need to know. 

Beginner Objective-C interview questions

What are the top beginner Objective-C interview questions? Here are the top questions to ask at your next interview. 

1. What are the main benefits of Objective-C?


The main benefits of Objective-C are: 

  • Dynamic typing. Dynamic typing helps simplify code and improve flexibility in class usage so that it’s possible to change the structure and purpose of classes during development processes. 

  • Established. Objective-C, as a language that has been used for more than 30 years, is well-tested with a large number of libraries. The code is reliable and questions are easily answered. 

  • Stability. Objective-C is mature and doesn’t release constant updates or new versions so developers don’t need to migrate their work to a new version every few months. 

  • Support for older versions. Objective-C works with earlier versions of iOS and macOS and is compatible with C languages. 

2. Is Objective-C a dynamic language? 


Yes, Objective-C is a highly dynamic language. This dynamism is based on three things – dynamic typing (deciding the object class at runtime), dynamic binding (deciding the method to be invoked at runtime), and dynamic loading (adding new modules to a program at runtime). 

Thanks to being dynamic, compile time and vital link-time constraints aren’t needed. The responsibility of source resolution is shifted to runtime when the client is in proper control. 

3. Explain the advantages and disadvantages of categories. 


The advantages of categories are that you can extend any class, even those for which there is no source, and categories provide you with a way to structure code across compilation units with local grouping. 

The disadvantage is that you can’t safely override methods that are already defined by class or another category. 

4. What are the types of protocols in Objective-C? 


There are two protocols, formal and informal. A formal protocol has its own declaration, adoption, and type-checking syntax, and declares a list of methods to implement. Required or optional methods can be designated with the @required or @optional keywords. Formal protocols can also adopt other protocols and they are an extension of Objective-C. 

Informal protocols are a category on NSObject, which makes almost all objects adopters of the protocol. Implementation of methods is optional. Before a method is invoked, the calling object checks to see if the target object implements it. 

Advanced Objective-C interview questions

What are some advanced Objective-C interview questions? These questions will help you get started. 

5. Explain when you should use categories instead of inheritance. When should you do the reverse? 


Use a category when you’re adding functions and not data. That way, you can attach functions to the class without creating a new relationship (creating a sub-class) and while preserving existing functionality. 

But if you need to add or change data and add functionality to manipulate data or change a functionality to represent a sub-type of object in your controller model, use sub-class. 

6. Explain the difference between active, inactive, not running, background, and suspended execution states. 


Active, which is typical for foreground applications, means that the application is running in the background and is accepting events. 

Inactive means that the application is running in the background, but isn’t accepting events. Applications that advance to an alternate state will typically remain in this state.

Not running means that the application hasn’t been launched or it was ended by a system as it was running.

Background means an application is running in the background or executing code, something that happens when applications approach being suspended. Applications that request additional execution time can stay in this state for a certain amount of time. And an application that’s launched out of the spotlight enters this state instead of the inert state. 

Suspended means that the application is out of sight when it’s not executing code. The system moves applications to this state consequently and doesn’t inform them before it happens. Applications that are suspended stay in memory but do not execute code. During a low-memory condition, the framework might cleanse suspended applications to make space for foreground applications. 

7. Explain what GrandcentralDispatch is. What are its advantages in comparison to NSThread? 


GrandcentralDispatch is a technology developed by Apple. It’s an implementation of task parallelism based on the thread pool pattern meant to optimize application support for systems with multi-core processors and other symmetric multiprocessing systems. 

GCD doesn’t necessarily offer better performance than threads, but the developer doesn’t have to think about creating threads or matching the number of available threads to the number of available processors. Many smaller tasks can be created that will execute as a processor becomes available and the system schedules those tasks for you. 

8. Explain when NSArray is used instead of NSSet. 


NSArray is faster than NSSet for holding and iterating, which is when NSArray is preferred instead of NSSet. However, NSArray should be avoided when testing for inclusion. Sets use hash values to find items while arrays iterate over their contents to find an object. If you need both iteration and testing, choose NSSet. But if you intend to keep the collection ordered and test for inclusion, keep two collections, NSArray and NSSet, with the same objects. 

9. Explain Objective-C blocks.


Objective-C blocks are language-level features, which make it possible to create segments of code to be passed to methods or functions as if they were values. Blocks are objects, so they can be added to collections like NSDictionary and NSArray. They can also capture value from the enclosing scope so they’re similar to closures and lambdas in other languages. 

Over to you!

There you have it! Now you know what the best Objective-C interview questions are. 

However, interviewing is the first step of the process. The next step is to assess your candidates. And that’s what CodeSubmit can help you with. 

CodeSubmit’s assessment tests are designed for identifying the right person for your team. We offer both take-home assignments and CodePair live coding.

Want to learn more? 

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