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iOS development is always advancing, boasting robust tools and frameworks built by and used for technology designed for Apple devices. These tools and frameworks facilitate the crafting of secure and user-friendly applications optimized for a plethora of devices such as iPhones, iPads, and Apple Watches. A remarkable landmark in this evolving landscape has been the advent of SwiftUI, a UI toolkit that simplifies the development process with its modern, declarative syntax.

Native iOS development holds a distinctive edge in cases where high-performance, fluid, and intuitive applications are a priority, leveraging the rich features and functionalities exclusive to iOS. Additionally, apps that aim to provide a premium user experience with superior graphical elements and animations often find their base in native development. Apple's commitment to quality and a user base with a penchant for high-end products make native iOS development a favorable choice for upscale, exclusive applications.

Swift and Objective-C are the cornerstones of iOS development. Introduced in 2014, Swift quickly became popular due to its modern syntax and enhanced safety features. On the other hand, Objective-C continues to be a stalwart in maintaining legacy projects, offering stability and a rich repository of resources.

Swift has rejuvenated iOS development, emerging as the prime choice for new endeavors. Conversely, Objective-C remains invaluable, especially in managing established projects with its proven history and comprehensive feature set.

Looking ahead, SwiftUI is poised for an upward trajectory in the iOS development sphere, promising to unveil unparalleled opportunities for businesses and developers while sustaining the preference for native development due to its inherent benefits.

Industries & applications of iOS

iOS development is ubiquitous, spearheading innovations in diverse sectors such as healthcare, education, entertainment, real estate, travel, and finance, among others.

Its capabilities empower various applications, from telemedicine and e-learning platforms to immersive gaming and streaming apps. Moreover, it facilitates seamless eCommerce experiences and robust enterprise solutions. SwiftUI’s emergence promises to spur further creativity and efficiency in app development across these sectors.

Must-have technical skills for iOS Developers

When looking for an iOS developer, make sure they have listed most of these skills in their resume:

• Proficiency in Swift is a MUST, It is also good to know Objective-C.
• Deep understanding of iOS frameworks such as UIKit and SwiftUI.
• Robust knowledge of different software architectural design patterns such as MVVM and MVC
• Experience with Auto Layout and Interface Builder for UI design.
• Knowledge of Apple's Human Interface Guidelines.
• Proficiency in various data storage options available in iOS, including, but not limited to, CoreData for structured data persistence, UserDefaults for lightweight data storage, and working with files and directories for saving data directly to the iOS file system. Experience with secure storage solutions such as Keychain for storing sensitive data and understanding of using external databases through APIs, equipping them to choose the best storage option based on specific project needs.
• Deep understanding of handling asynchronous code with different approaches such as Callbacks, Promises, Async/Await, or frameworks like Combine and RxSwift to manage complex asynchronous operations efficiently and maintain a clean, readable code base.
• Familiarity with design patterns such as Coordinator, Builder, Factory Method, Strategy, Singleton, Decorator, and Delegate.

Nice-to-have technical skills for iOS Developers

When looking for a way to separate the great from the good developers, here are some telltale signs that you are dealing with an absolute pro. Look out for these skills in their resume:

• Experience with third-party libraries and APIs, such as Alamofire, for network programming.
• Skills in working with tools like CocoaPods, Carthage, or Swift Package Manager for dependency management.
• Proficiency in writing unit and UI tests using XCTest framework.
• Experience with continuous integration and continuous deployment (CI/CD) pipelines.
• Familiarity with reactive programming paradigms, utilizing frameworks such as Combine or RxSwift.

Interview questions for iOS Developers and their expected answers

Here are some interview questions you can use to evaluate the knowledge of your iOS Developer candidates.

1. Question: What is the difference between struct and class in Swift, and when would you use one over the other?

Answer: In Swift, struct is a value type, while class is a reference type. This means that structs are copied when passed around in your code, while classes are passed by reference, pointing to the same memory location. Structs are typically used for simpler, immutable data models, while classes can be used to create mutable, more complex objects with functionalities like inheritance.

2. Question: What are Swift protocols, and how are they used in iOS development?

Answer: Protocols in Swift define a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality. Classes, structures, and enumerations can adopt protocols to provide an actual implementation of those requirements. It's a way to enforce a certain level of conformity to a set of functionalities, promoting reusability and flexibility in the codebase.

3. Question: Could you explain how Grand Central Dispatch (GCD) works in iOS?

Answer: Grand Central Dispatch (GCD) is a low-level API for managing concurrent operations. It helps you improve your app’s responsiveness by allowing it to perform multiple tasks simultaneously on different cores of the processor. GCD provides and manages queues of tasks that can be executed either serially or concurrently, optimizing the application’s performance and responsiveness by efficiently utilizing system resources.

4. Question: Can you explain the Optional concept in Swift and why it's used?

Answer: Optionals in Swift are types that can hold either a value or no value (nil). They indicate the absence of a value or a meaningful default. Handling optionals correctly is crucial to avoid runtime crashes due to nil value dereferencing, making the code safer and more predictable.

5. Question: Describe how memory management is handled in Swift.

Answer: Swift uses Automatic Reference Counting (ARC) to track and manage an application’s memory usage. Whenever a new class instance is created, ARC allocates memory to store information about that instance. When an instance is no longer needed, ARC frees up the memory used by that instance to make it available for other resources, preventing memory leaks and optimizing performance.

6. Question: Describe various data storage options available in iOS and discuss the pros and cons of each.

Answer: OS provides several data storage options, each suited to different use cases:

• UserDefaults: Suitable for storing simple data types and small amounts of data. It's easy to use but not secure for sensitive data.
• Core data: A robust framework for managing and persisting a graph of objects. It supports complex queries but has a steeper learning curve.
• File system: Directly interacting with the file system allows for storage of larger data but requires manual management of files and directories.
• Keychain services: Secure storage for sensitive data like passwords and tokens, but has a more complex API.
• SQLite and third-party databases: Flexible and powerful for various data storage needs but may require additional setup and management.

7. Question: When would you use Swift's Result type?

Answer: Swift's Result type is utilized when a function can succeed or fail. This is especially common in asynchronous operations requiring error handling, such as network requests or file system interactions. The Result type encapsulates the success value or the error information, making the function's outcome explicit and easier to handle than throwing errors or using optionals.

8. Question: Can you explain Key-Value Observing (KVO) and its use on Apple's platforms?

Answer: Key-value observing (KVO) is a mechanism by which objects can be notified of changes to specified properties of other objects. This pattern is useful for creating reactive behaviors within an app. KVO is a part of Apple's Cocoa programming paradigm and relies on the Objective-C runtime, though it can also be used in Swift to a limited extent.

Here’s an overview of how KVO operates and how it can be used:

• Observation setup: An observer object registers itself to be notified of changes to a specific property (or key path) of another object, known as the observed object.
• Notification: When the observed property changes, the observer is notified, often by having a method called on it.
• Handling changes: The observer can then query the observed object for the new value of the property, and take whatever action is necessary in response to the change.

KVO is often used in situations where one part of an app needs to react to changes in another part, without needing to establish tighter coupling between the two parts.

9. Question: When using arrays in Swift, what’s the difference between map() and compactMap() functions?

Answer: map() is used for straightforward transformations of every element in an array, while compactMap() is used when the transformation might result in nil and you want to filter out these nil values, producing an array of unwrapped non-nil results. For example, converting an array of strings into integers works better with compactMap(), because creating an Int from a String is failable.

10. Question: How can App Transport Security (ATS) enhance the security of an iOS application, and what are the steps to configure it?

Answer: App Transport Security (ATS) is a feature introduced by Apple to promote secure network communication in iOS applications, primarily by enforcing HTTPS instead of HTTP. By default, ATS is enabled in new projects created in Xcode, enhancing data privacy through encrypted data transmission and helping prevent Man-in-the-Middle (MitM) attacks. To configure ATS, developers may need to specify exceptions in the app's Info.plist file, primarily if the app interacts with servers that do not support the latest SSL or TLS protocols. However, loosening ATS restrictions should be done cautiously, as it can weaken the app's security. It's essential to thoroughly test the app's network communication under the configured ATS settings and ensure the server configuration adheres to modern cryptographic standards. Through diligent configuration and testing, developers can leverage ATS to significantly bolster the network security of their iOS applications.

Business benefits of iOS development

Of course, companies wouldn't use iOS as the basis of their applications if it didn’t come with a wide array of beneficial aspects. Here are the main three reasons why you should use iOS.

• Higher revenue potential: iOS users tend to spend more on app purchases, offering a potentially higher revenue stream for businesses targeting this audience.
• Secure and stable environment: iOS offers a secure and stable development environment, which can translate to apps with fewer bugs and vulnerabilities.
• Loyal user base: iOS enjoys a loyal user base, which can offer businesses a stable and engaged audience for their apps.

Qualifications and skills an iOS Developer must have

To summarize, the essential skills and tools a good iOS developer should be equipped within their career to be able to build iOS-based applications successfully are:

• Programming skills: Proficiency in Swift and/or Objective-C, with a strong understanding of object-oriented programming and SOLID principles.
• Framework knowledge: Deep understanding of essential iOS frameworks like UIKit and SwiftUI.
• Design skills: An eye for pixel-perfect design, ensuring the development of aesthetically pleasing and user-friendly interfaces.
• Continuous learning: A dedication to continuous learning, keeping up with the latest advancements and best practices in the iOS development ecosystem.
• Collaborative skills: Ability to work well in a team, with a strong grasp of version control systems like Git for collaborative development.
• SOLID Principles: Familiarity with SOLID principles to craft maintainable and robust software architectures.