10 iOS Developer interview questions and answers

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Name four important data types found in Objective-C.

Four data types that you’ll definitely want your developer to be aware of are as follows:

  • NSString: Represents a string.
  • CGfloat: Represents a floating point value.
  • NSInteger: Represents an integer.
  • BOOL: Represents a boolean.

How proficient are you in Objective-C and Swift? Can you briefly describe their differences?

When Swift was first launched in 2014, it was aptly described as “Objective-C without the C.” By dropping the legacy conventions that come with a language built on C, Swift is faster, safer, easier to read, easier to maintain, and designed specifically for the modern world of consumer-facing apps. One of the most immediately visible differences is the fact that Objective-C lacks formal support for namespaces, which forces Objective-C code to use two- or three-letter prefixes to differentiate itself. Instead of simple names like “String,” “Dictionary,” and “Array,” Objective-C must use oddities like “NSString,” “NSDictionary,” and “NSArray.” Another major advantage is that Swift avoids exposing pointers and other “unsafe” accessors when referring to object instances. That said, Objective-C has been around since 1983, and there is a mountain of Objective-C code and resources available to the iOS developer. The best iOS developers tend to be pretty well versed in both, with an understanding that Swift is the future of iOS development.

What are UI elements and some common ways you can add them to your app?

Buttons, text fields, images, labels, and any other elements that are visible within the application are called UI elements. These elements may be interactive and comprise the user interface (hence the term "UI") of an application. In iOS development, UI elements can be quickly added through Xcode’s interface builder, or coded from scratch and laid out using NSLayoutConstraints and Auto Layout. Alternatively, each element can also be positioned at exact coordinates using the UIView "(id)initWithFrame:(CGRect)frame" method.

Explain the purpose of the reuseIdentifier in the UITableViewCell constructor:

  (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier

The reuseIdentifier tells UITableView which cells may be reused within the table, effectively grouping together rows in a UITableView that differ only in content but have similar layouts. This improves scroll performance by alleviating the need to create new views while scrolling. Instead the cell is reused whenever dequeueReusableCellWithIdentifier: is called.

What are some common execution states in iOS?

The common execution states are as follows:

  • Not Running: The app is completely switched off, no code is being executed.
  • Inactive: The app is running in the foreground without receiving any events.
  • Active: The app is running in the foreground and receiving events.
  • Background: The app is executing code in the background.
  • Suspended: The app is in the background but is not executing any code.

What is the purpose of managed object context (NSManagedObjectContext) in Objective-C and how does it work?

Managed object context exists for three reasons: life-cycle management, notifications, and concurrency. It allows the developer to fetch an object from a persistent store and make the necessary modifications before deciding whether to discard or commit these changes back to the persistent store. The managed object context tracks these changes and allows the developer to undo and redo changes.

Determine the value of “x” in the Swift code below. Explain your answer.

  var a1 = [1, 2, 3, 4, 5]
  var a2 = a1
  a2.append(6)
  var x = a1.count

In Swift, arrays are implemented as structs, making them value types rather than reference types (i.e., classes). When a value type is assigned to a variable as an argument to a function or method, a copy is created and assigned or passed. As a result, the value of "x" or the count of array "a1" remains equal to 5 while the count of array "a2" is equal to 6, appending the integer "6" onto a copy of the array "a1." The arrays appear in the box below.",

  a1 = [1, 2, 3, 4, 5]
  a2 = [1, 2, 3, 4, 5, 6]

Find the bug in the Objective-C code below. Explain your answer.

  @interface HelloWorldController : UIViewController

  @property (strong, nonatomic) UILabel *alert;

  @end

  @implementation HelloWorldController

  - (void)viewDidLoad {
    CGRect frame = CGRectMake(150, 150, 150, 50);
    self.alert = [[UILabel alloc] initWithFrame:frame];
    self.alert.text = @"Hello...";
    [self.view addSubview:self.alert];
    dispatch_async(
      dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
      ^{
        sleep(10);
        self.alert.text = @"World";
      }
    );
  }
  @end

All UI updates must be performed in the main thread. The global dispatch queue does not guarantee that the alert text will be displayed on the UI. As a best practice, it is necessary to specify any updates to the UI occur on the main thread, as in the fixed code below:

  dispatch_async(
  dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
  ^{
  sleep(10);
  dispatch_async(dispatch_get_main_queue(), ^{
  self.alert.text = @"World";
});
});

Explain the difference between raw and associated values in Swift.

This question tests the developer’s understanding of enumeration in Swift. Enumeration provides a type-safe method of working with a group of related values. Raw values are compile time-set values directly assigned to every case within an enumeration, as in the example detailed below:

enum Alphabet: Int {
  case A = 1
  case B
  case C
}

In the above example code, case "A" was explicitly assigned a raw value integer of 1, while cases "B" and "C" were implicitly assigned raw value integers of 2 and 3, respectively. Associated values allow you to store values of other types alongside case values, as demonstrated below:

enum Alphabet: Int {
  case A(Int)
  case B
  case C(String)
}

You’ve just been alerted that your new app is prone to crashing. What do you do?

This classic interview question is designed to see how well your prospective programmer can solve problems. What you’re looking for is a general methodology for isolating a bug, and their ability to troubleshoot issues like sudden crashes or freezing. | In general, when something goes wrong within an app, a standard approach might look something like this: | | ------ | | Determine the iOS version and make or model of the device. | | Gather enough information to reproduce the issue. | | Acquire device logs, if possible. | | Once you have an idea as to the nature of the issue, acquire tooling or create a unit test and begin debugging. | A great answer would include all of the above, with specific examples of debugging tools like Buglife or ViewMonitor, and a firm grasp of software debugging theory—knowledge on what to do with compile time errors, run-time errors, and logical errors. The one answer you don’t want to hear is the haphazard approach—visually scanning through hundreds of lines of code until the error is found. When it comes to debugging software, a methodical approach is a must.

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    Robert C.
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    • 5.0
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    Over 25 years in professional game development plus 10 years in enterprise software development. Have worked at Sony, EA/Maxis, 2K Sports, Cisco Systems, VMware and Google as everything from individual contributor to Applications Architect, Founder, and CTO. I use HTML5, CSS3, JavaScript coded closely to the DOM without frameworks (ReactJS, AngularJS, etc.) to deliver solutions for my clients. HTML5, CSS3, JavaScript, TypeScript, ES2022 C/C++/C#/Objective C MongoDB, Redis, MySQL, ORACLE Node.js, ExpressJS, Passport Unity3D
  • $70 hourly
    Tudor-Mihai A.
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    • 5.0
    • (9 jobs)
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    - fully embraced SwiftUI; - big on modular codebases and clean architecture flavors - usually taking the lead in development and taking initiative product wise - ish at designing screens out of just ideas, but great as a critical eye over provided design
  • $35 hourly
    Kamaljeet S.
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    • 4.9
    • (37 jobs)
    Ambala, HARYANA
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    👋 Hey, I'm a Senior iOS Developer with over 8 years of diverse software development experience in tech. From developing to leading, I have done it all! I am proficient in creating apps for iOS and well-versed in developing frontends and backends. Beyond iOS, I led teams in various tech companies. My expertise spans numerous industries, and I've partnered with remarkable companies from all around the globe. I know a vast array of technologies and tools that I have used to create some pretty amazing applications! My Services: 🤖 AI integration | OpenAI ChatGPT, Microsoft AzureAI, Google Cloud, OpenCV 🕶️ AR/VR integration | Lidar, RoomPlan(Floor Plan), ARKit(Augmented Reality), Vision Framework 📲 VoIP integration | LinPhone, Microsoft Azure, Agora, WebRTC 🧠 Tech Advisor 🌐 Backend Development Firebase Who I work with: 🚀 Startups – take your idea through the startup lifecycle within a reasonable budget and timeline. 🙋 Small and Medium Businesses – acquire software excellence to boost your current product. Results: ✅ Developed apps with over 200,000+ monthly active users. ✅ A startup gained early adopters for their MVP using TestFlight ✅ A product company increased its user base by 40% by scaling its app onto a new platform. ✅ A services company grew its profits by 60%, thanks to an iOS streaming app. Working with me, you will get: 🕵️ Transparent process with various tracking tools and regular meetings. 💬 Prompt responses and concise explanations. 🧠 Expert consulting and tailored advice based on your specific needs. 🔄 Smooth integration with existing workflows and effective collaboration with your team. 🌍 Flexibility to work with clients across different time zones. 📚 Thorough documentation and dedicated support throughout the transition period. A very important message to any customer who could be working with me: “I take your project as my project” so I always will be 100% dedicated to successful project completion. ►► 𝐇𝐀𝐕𝐄 𝐐𝐔𝐄𝐒𝐓𝐈𝐎𝐍𝐒? 𝐈𝐍𝐕𝐈𝐓𝐄 𝐌𝐄 𝐀𝐍𝐃 𝐀𝐒𝐊!◄◄
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