Swift iOS interview questions and answers – Part 5 – Architectural & Design pattern

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Part 5 consists Swift iOS interview questions and answers of design and architectural pattern. In this article, I will cover the different concepts of design and architectural pattern briefly such as MVC, MVVM, VIP, VIPER, structural, behavioural and creational design pattern in iOS etc.

What is MVC and explain the main concern of MVC?

MVC/Model-View-Controller is an architectural pattern used to decouple user-interface (view), data (model), and application logic (controller). The main concern of MVC is that it does not enforce developers to decouple responsibilities. For example: network related codes are often found in ViewController. ViewController is treated as dumping station for all kind of logics sometimes. For this reason, MVC is often called massive view controller.

MVC roles are described here –

• Model will only encapsulates the data, it must not contain any business logic.
• View will encapsulate what user can see in the UI and it also should not have business logic.
• Controller should maintain all kinds of business logic that goes between the View and the Model.

Explain OOP in the context of an iOS developer

Object-oriented programming (OOP) is a programming paradigm that uses objects and their interactions to design applications and computer programs. In the context of iOS development, OOP is used to build the structure and functionality of iOS applications using the Objective-C or Swift programming languages. iOS developers use OOP principles such as inheritance, encapsulation, and polymorphism to create classes and objects that interact with each other to provide the desired functionality of the application. OOP also allows for code reuse and makes it easier to maintain and update the application.

Read more: Refine your OOP skills for iOS Development

What is MVVM?

MVVM/Model-View-ViewModel is an architectural pattern that enables you to separate the business and presentation logic from its UI. Creating the clean separation will help you to find bugs easily and to test effectively. MVVM will be a good choice if you want to shrink the size of your view controller and make the business logic more readable.

The View Model invokes changes in the Model and updates itself with the updated Model, and since we have a binding between the View and the View Model, the first is updated accordingly.

How would you explain the concept of dependency injection to a junior developer?

Dependency injection is a way to provide a class with its dependencies, instead of having the class create or look for them itself. It helps to make the code more flexible and easier to test by allowing dependencies to be swapped out as needed. For example, a class that performs network requests could be given an instance of a networking class, rather than having to create one itself.

Can you explain the principles of protocol-oriented programming to a new Swift developer?

Protocol-oriented programming is a programming paradigm that emphasizes using protocols, rather than classes, to define the interface and behavior of types. It allows for more flexibility in terms of implementation and allows for protocol-based polymorphism. For example, a protocol could be defined for a “Drawable” object, and any object that conforms to that protocol can be drawn on screen.

Can you describe the use of Key-Value Observing (KVO) on Apple’s platforms?

KVO (Key-Value Observing) allows objects to be notified when the value of a property changes. It’s used on Apple’s platforms, such as iOS and macOS, for data binding and for detecting changes in data. For example, an application’s user interface can be bound to a data model, and when the data model’s properties change, the user interface updates automatically.

Can you provide some scenarios where the use of singletons would be appropriate?

Singletons are a design pattern where a class is instantiated only once throughout the lifetime of the application. They can be a good idea when a single instance needs to manage shared resources, such as a shared database connection or a shared configuration. Singletons can also be used for logging, as well as for implementing a shared cache.

What is design pattern and explain briefly some commonly used Cocoa design patterns?

Design patterns are reusable solutions to common problems in software design. Design patterns can speed up the development process by providing tested, proven development paradigms. Effective software design requires considering issues that may not become visible until later in the implementation. Reusing design patterns helps to prevent subtle issues that can cause major problems and improves code readability for coders and architects familiar with the patterns.

Commonly used Cocoa design patterns are –

Creational Design Pattern: Singleton, Factory
Structural Design Pattern: Decorator, Adapter, Facade
Behavioral Design Pattern: Observer, Memento.

What is Singleton Pattern and why should we avoid over using it? 

The singleton pattern(Creational) guarantees that only one instance of a class is instantiated for the lifetime of the application. It is very easy pattern to implement but it also has bad reputation to misuse. Singleton kills the idea of “separation of concern” as it can be accessed from everywhere(They are generally used as a global instance). Singleton violates the single responsibility principle and makes the code very tightly coupled.

Why singletons are bad for testing?

Singletons are a problem from a testing perspective. They tend to make isolated unit-tests difficult to write because one test can change the global value which is not valid for other tests.

When using the delegation pattern, why is the delegate variable weak?

So that it doesn’t maintain a reference to an object that it has no right to retain.

What would be better approach than Singleton?

Inversion of control (IoC) and dependency injection are patterns meant to overcome the problems of singleton in an object-oriented manner.

What is Decorator Design Pattern ? 

The decorator design pattern(Structural) dynamically adds behaviours and responsibilities to an object without modifying its code. Unlike inheritance, decorated objects are not limited by their parent classes. Putting in other terms, a client has control over how and when to decorate the component. This pattern is simply achieved by using protocol in Swift.

What is factory method in Swift?

Factory method is a creational design pattern which solves the problem of creating objects without specifying their concrete classes.

What is Facade Design Pattern ? 

The facade design pattern provides a single interface to a complex subsystem. Instead of exposing the user to a set of classes and APIs, you only expose one simple unified API. In Swift, you can achieve this pattern using extensions and delegation.

What is the Anti-pattern?

An anti-pattern is used with a belief that it will solve particular problem but in a long run it will create more liabilities than benefits. The patterns that are considered bad software development practices are anti-patterns. Sometimes singleton is considered as an anti pattern due to it’s misuse.

What are the basic differences between creational, structural and behavioural pattern?

The creational pattern provides way to create objects while hiding the creational logic which offers the flexibility for creating objects based on different use cases.

The structural pattern helps us to manage classes and object together to create larger components.

The behavioural pattern helps us to provide better communication between objects and increase flexibility between object.

What is Adapter Pattern? 

The adapter design pattern allows two objects, with related functionalities, to work together, even when they have incompatible interfaces. Adapter allows the objects to cooperate with other objects where they could not normally work with due to different interfaces. It is a structural design pattern which is useful for composing classes and objects into a larger system. Swift does not support multiple inheritance but Swift supports conformance to multiple protocols, you can implement adapter pattern by using protocols.

What is Observer Pattern ? 

Observer pattern is a behavioural design pattern where the objects can notify other objects about the changes in their state. The Observer pattern provides a way to subscribe and unsubscribe to and from these events for any object that implements a subscriber interface.
We can implements the observer pattern in two ways in Swift – Notifications and Key-Value Observing.

What is the delegation pattern?

Delegation is a design pattern that enables a class or structure to hand off (or delegate) some of its responsibilities to an instance of another type. The delegating object typically keeps a reference to the other object (delegate) and sends a message to it at the appropriate time.

Fellow iOS Developers, Please Keep In Mind

  • It’s important to keep in mind a few key points as you prepare for your interview. Firstly, it’s worth noting that there are over 1000 interview questions available in the interview section for you to review and prepare for. While reading the question, take the time to carefully consider your answer and think about the information that you want to convey. The answer provided here in this blog can be explained in a different way. You should also prepare your examples.
  • It’s also important to remember that these interview questions are not meant to be difficult. The interviewer is not looking to challenge you, but rather to start a conversation that will allow your abilities and interests to come to the forefront. They want to get to know you and your experience better.
  • Finally, it’s crucial to avoid simply answering questions with a “yes” or “no.” Interviewers are looking for more in-depth responses that include basic understanding, reasoning, explanation, and examples. So, make an effort to elaborate on your answers and provide specific, relevant information to support your response. This will demonstrate your thoughtfulness and show the interviewer that you are well-prepared for the interview.

These links are for a series of interview questions and answers related to SwiftUI and iOS development. Part 1 covers UI basics, Part 2 covers advanced UI topics, and Part 3 covers data-related concepts. The Swift iOS interview questions and answers series is also included, with 5 parts covering various topics related to iOS development. Additionally, there is a bonus section for iOS developer interview questions.

SwiftUI Interview Questions and Answers – Part 1 – UI Basics

SwiftUI Interview Questions And Answers – Part 2 – UI Advance

SwiftUI Interview Questions And Answers – Part 3 – Data

If you are interested in 5 parts Swift Series 

Swift iOS interview questions and answers

Swift iOS interview questions and answers – Part 1

Swift iOS interview questions and answers – Part 2

Swift iOS interview questions and answers – Part 3

Swift iOS interview questions and answers – Part 4

Swift iOS interview questions and answers – Part 5

and a bonus

iOS Developer – Bonus Interview Questions

Planning to apply for iOS job? Check out this article to uplift your resume! Happy job hunting!

✍️ Written by Ishtiak Ahmed

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