iOS Developer Interview Questions
iOS developers create applications powered by Apple’s iOS operating system. This operating system works on multiple devices across Apple’s platform, including the iPad, iPhone, and iPod.
iOS operates using either swift or objective-C, so an iOS developer must be proficient in at least one of these programming languages. iOS developers are involved in the development of an application across all layers of its infrastructure and should be prepared to work with other developers.
iOS developer responsibilities may include:
- Designing applications for the iOS platform
- Working with other software engineers
- Maintaining appropriate code quality
- Testing out applications to fix bugs
- Automating processes within the application
iOS is rapidly becoming one of the most popular systems in the world. In order to deliver a positive user experience, skilled iOS developers will:
- Possess expert knowledge of relevant programming languages
- Communicate effectively with team members
- Possess an eye for detail in order to identify broken code
- Provide troubleshooting services as needed
- Communicate relevant timelines and milestones to employers
A bachelor’s degree in computer science or a similar field is preferred for entry-level jobs, but candidates with work experience who demonstrate an understanding of the iOS platform are not uncommon. There are many extra certifications or supplementary courses candidates can take to gain further marketable skills.
If you’re getting ready to interview for a position as an iOS developer, you can prepare by researching the company as much as possible. Learn about the 9 things you should research before an interview.
Salaries for iOS developers range between $54K and $86K with the median being $68K.
Factors impacting the salary you receive as an iOS developer include:
- Degrees (associate's or equivalent technical training, bachelor's, master's, etc.)
- Years of Experience
- Reporting Structure (seniority of the manager you report to and number of direct reports)
- Level of Performance - exceeding expectations
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iOS Developer Interview Questions
Question: Can you discuss the difference between synchronous and asynchronous tasks within iOS?
Explanation: This is a technical question asking you to define the differences between two similar terms used in this profession. As an iOS developer, you can anticipate that the majority of the interview will be technical questions. Technical questions are best answered succinctly and directly with little embellishment. The interviewer will ask a follow-up question if they need additional information.
Example: “Within iOS, tasks are either synchronous or asynchronous. If the task is synchronous, it waits until a previous task is completed before proceeding. In the case of asynchronous tasks, the tasks function simultaneously in the background. You are notified when background tasks are completed.”
Question: Under what conditions would you designate a task as synchronized?
Explanation: This is a follow-up to the previous question. During an interview, you should anticipate follow-up questions, especially with technical questions. Keeping your answer brief will encourage the interviewer to ask follow-up questions to explore the topic in more detail.
Example: “Designating a task as synchronous will ensure only one thread is executing at a time. This will improve the performance of that task and eliminate any conflicts which may occur if several tasks were running asynchronously.”
Question: What is the function of a completion handler, and how do you use it when developing iOS applications?
Explanation: This is a hybrid technical and operational question. It starts by asking you to define a term and then discuss how that term is used in the work you do. Operational and hybrid questions are answered in the same manner as technical ones. You can anticipate follow-ups to these questions as well.
Example: “A completion handler is code that will notify the application when an operation such as an API call is finished. It tells a program that the next process needs to be executed. The way a completion handler functions is to examine a piece of code for three different arguments, including NSData?, NSURLResponse?, and NSError?. If all three of them return a null value, the function is considered completed.”
Question: Can you describe what enum or enumerations are?
Explanation: The interviewer is asking another technical question. You can prepare for technical questions by reviewing the job posting to determine what skills and experience are needed for this position. You can also research the company, its products, and services. This should provide you an idea of the type of technology they employ. Once you know this, take some time to study standard terms, processes, and procedures used for iOS development.
Example: “Enum or enumerations track the state of an application and how it is being used at that moment. This is important when developing an application because it helps you keep track of what processes are being executed and what resources are required. Enumerations can bundle individual values and multiple states to provide a comprehensive picture of exactly what is going on at any given moment while the application is running.”
Question: Why is it recommended that you not use a strong for enum property in objective-C?
Explanation: You probably recognize this as a follow-up to the previous question. We have noted that you should always anticipate follow-up questions during an interview. Keeping your answer short and to the point will encourage the interviewer to ask a follow-up question for the topic which you are discussing. This will enable you to guide the interviewer into areas you are comfortable talking about or in which you have a lot of knowledge.
Example: “The main reason we don’t recommend using either a strong or a weak for a property of the enum is that enums are not objects, and therefore, you don’t need to specify a strong or weak condition for them.”
Question: Can you talk about the difference between strong, weak, read-only, and copy?
Explanation: The answer to your previous question prompted the interviewer to ask another follow-up question. While this addresses a slightly different topic, it feeds off your previous answer and illustrates the point of you being able to guide the interview in a specific direction.
Example: “Each of these terms defines a property or characteristic for a command or line of code. Strong and weak define how the memory of the property will be managed. Strong maintains the reference to a property throughout the life of an object. Weak indicates the use of the object as a reference, but not maintained. Read-only defines the property of an object. Copy indicates the object is being copied, and therefore, its value cannot change throughout the life of the operation.”
Question: Please define the term dynamic dispatch and discuss how it is used.
Explanation: This is a classic technical question, which asks you first to define a term and then discuss how it is used. By now, you are starting to recognize technical, operational, and general questions. Knowing the type of question will help you formulate and structure your answer.
Example: “Dynamic dispatch refers to the process of deciding which implementation of a multi-functional operation will be called during a process. It enables an operation to have several implementations that can be called by the program at any time, depending on what the programmer is trying to achieve. Dynamic dispatch needs to be implemented by the programmer because it is not a default value.”
Question: What steps do you take to ensure the usability in designing an iOS application?
Explanation: Sometimes, developers can become myopic, focusing on the functions, operations, and processes within an application. You cannot lose sight of the fact that the application eventually needs to be used. Designing in the usability is a crucial feature of an iOS developer, and you should be able to describe the process you use to do this.
Example: “I agree that it is sometimes easy to lose sight of the fact that the application is going to be used by a person. To avoid building in too much technology and not enough user experience into an application, I take the following steps - first, I try to think like the user and not a developer. I also remember that users are individuals and not a set of demographics. I then think about the situation under which the application will be used and the environment in which it will function. Finally, I seek to test the user experience after the application is launched and continue to refine it to make it more user friendly.”
Question: How is the property @dynamic used in objective-C processes?
Explanation: This technical question asks you about a precise operation with the objective-C programming environment. As the interview progresses, the technical questions will become more complicated and more specific. This is an indication the interviewer is gaining confidence in your qualifications and is willing to explore more technically challenging areas.
Example: “Dynamic is a property used for subclasses of the NSManagedObject. It tells the compiler that getter and setter commands are implemented elsewhere in the code.”
Question: What does the @synthesize command do with objective-C?
Explanation: Only experienced iOS developers will recognize this as a follow-up question to the previous one. Although it asks about a specific command within the objective-C environment, it also refers to the topic which you just discussed in your previous answer. This illustrates the different ways interviewers will ask you technical questions to determine the scope of your knowledge and the depth of your experience in this profession.
Example: “The command @synthesize generates getter and setter methods within the property. It works in conjunction with @dynamic command.”
Additional iOS Developer Interview Questions
What are app states? Could you explain them to me?
What is an iPhone reference library?
What are B-Trees?
Can you work under pressure and meet strict deadlines?
Can you describe OO programming?
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