SwiftUI Interview Questions and Answers – Part 1 – UI Basics

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SwiftUI is a powerful tool for creating intuitive and beautiful user interfaces on Apple platforms. In this series of blog posts, we’ll be covering some common SwiftUI interview questions and answers to help you prepare for your next job interview.

In Part 1 of this series, I’ll focus on the basics of SwiftUI, including topics such as the structure of a SwiftUI app, layout, and views. Whether you’re an experienced iOS developer looking to learn more about SwiftUI or a beginner looking to get started with iOS development, these interview questions and answers will give you the knowledge and confidence you need to succeed in your next job interview. In the article, I will focus on very basic interview questions of SwiftUI. Most of the questions and answers will help you to think from a different perspective than traditional UIKit. Though SwiftUI is a new paradigm, some of the companies have already moved toward SwiftUI to develop new features/UIs(Thanks to UIViewRepresentable). I will update this article with more questions in the future. 

What is the structure of a SwiftUI app and how does it differ from a UIKit app?

In a SwiftUI app, the main entry point is the SceneDelegate, which sets up the initial UI of the app and manages the lifecycle of the app’s scenes. The main difference between SwiftUI and UIKit is that SwiftUI uses a declarative syntax, meaning that you describe the desired state of the UI rather than manually updating it through code.

How do you create and customize views in SwiftUI?

To create a view in SwiftUI, you use a view struct, which is a struct that conforms to the View protocol. You can customize the appearance of a view by using various modifiers, which are functions that return a modified copy of the original view.

What is implicit stacking?

Implicit stacking in SwiftUI

What are the different layout options available in SwiftUI and when should you use each one?

There are several layout options available in SwiftUI, including VStack, HStack, ZStack, List, and Form. You should use VStack and HStack for vertical and horizontal layouts, respectively, ZStack for overlaying views, List for creating a scrolling list of items, and Form for creating a form-like layout.

How would you create programmatic navigation in SwiftUI?

To create programmatic navigation in SwiftUI, you can use the NavigationView and NavigationLink components to create a navigation stack, or use the NavigationLink component to create a link to another view.

SwiftUI: Answering the Big Question – Is UIKit replaced by SwiftUI?

Debunk SwiftUI myth – Frequently asked questions

What is the purpose of the ButtonStyle protocol?

The ButtonStyle protocol is used to customize the appearance and behavior of buttons in a SwiftUI app. By conforming to this protocol, you can create custom styles for buttons that can be reused throughout your app.

When would you use GeometryReader?

GeometryReader is used when you need to access the size and position of a view’s frame in order to create custom layouts or animations. Read more: Mastering GeometryReader in SwiftUI

Why does SwiftUI use structs for views?

SwiftUI uses structs for views because structs are value types, and this allows for efficient and safe management of the view’s data and state. This also allows for better performance and memory management in the app.

When should you consider SwiftUI over UIKit for your next project?

SwiftUI vs UIKit – Benefits and Drawbacks of SwiftUI

Top 10 Pros and Cons of SwiftUI

How do you respond to user interactions in SwiftUI?

You can use the onTapGesture() modifier to respond to tap gestures, and the onLongPressGesture() modifier to respond to long press gestures. You can also use the .onReceive() method to respond to external events, such as notifications or changes in the environment.

How do you integrate SwiftUI views into a UIKit project?

How does SwiftUI relate/correlate with storyboards?

You can use the UIHostingController class to wrap a SwiftUI view and present it in a UIKit app. You can also use the UIViewRepresentable protocol to create a wrapper for a UIKit view that can be used in a SwiftUI app.

Does the order of SwiftUI modifiers matter?

The order of SwiftUI modifiers can be important in certain cases. Modifiers that alter the environment in which the target view will be rendered usually do not have an order dependency. However, if a modifier can only be applied to a specific type of view, it must be placed directly on that type of view. Modifiers that wrap their target view often rely on a specific order to achieve the desired result, and changing the order can result in significant differences in the final output. Use of custom view modifier for reusability in SwiftUI

How do you customize view transitions in SwiftUI?

You can use the .transition() modifier to customize the transition between two views. You can specify the type of transition, such as .slide, .move, or .scale, and the direction of the transition, such as .leading, .trailing, .top, or .bottom.

What benefits does SwiftUI offer for iOS development?

SwiftUI offers several advantages for iOS development, including a more streamlined and intuitive syntax, improved performance, and better integration with other Apple platforms such as macOS and watchOS. Additionally, SwiftUI features a live preview feature that allows developers to see changes in their code in real-time, which can speed up the development process.

How do Xcode Previews improve the speed of iOS development and what are they used for?

Xcode Previews is a feature in Xcode that allows developers to see the results of their SwiftUI code in real-time, without the need to build and run the app on a simulator or device. This can save a lot of time and make the development process more efficient. It allows the developer to see the changes live in the preview pane, and it also enables them to make changes in the preview, that will automatically reflect in the code.

What are the methods for creating views and applying styling in SwiftUI?

In SwiftUI, views are created using structs that conform to the View protocol. These structs can contain other views, which can be combined to create complex user interfaces. Styles can be applied to views using modifiers, which are methods that can be chained together to apply multiple styles to a single view. For example, a text view can be given a font and a color using the .font() and .foregroundColor() modifiers.

Is SwiftUI ready for use in production environments?

SwiftUI was introduced in iOS 13, and since then has been used in many apps, and it is considered production-ready. However, as with any new technology, it is always a good idea to thoroughly test your app before releasing it to the public.

Can SwiftUI be used as a replacement for UIKit in iOS development?

SwiftUI is not a direct replacement for UIKit, but it offers a new way to build user interfaces for iOS and other Apple platforms. Some developers may choose to use SwiftUI for new projects, while others may continue to use UIKit for existing projects or for more complex interfaces. SwiftUI is designed to work alongside UIKit, so developers can use both in the same app as per their requirement.

Why does SwiftUI use structs for views?

SwiftUI uses structs for views due to the benefits they offer in terms of performance and thread-safety. Structs are preferred over classes when they are small and can be easily copied, as this eliminates the risk of multiple references to the same instance and potential memory leaks or conflicts when multiple threads try to access or modify a shared instance. In a multithreaded environment or when passing a variable between many classes, using structs ensures that a copy of the variable is always sent, rather than a reference to the original instance, which can prevent unintended changes to the variable’s value.

How do you work with data in SwiftUI?

You can use the @ObservedObject property wrapper to bind a view to a data model that conforms to the ObservableObject protocol. You can also use the @State property wrapper to bind a view to a simple piece of state, such as a toggle switch.

How do you create custom views in SwiftUI?

You can create custom views in SwiftUI by creating a struct that conforms to the View protocol and implementing the body property. You can also create custom modifiers by creating a function that returns a modified copy of the original view.

How do you debug a SwiftUI app?

You can use the Xcode debugger to debug a SwiftUI app, just like you would with a UIKit app. You can also use the print() function to print debug messages to the console, and the Previews feature to preview your views in the design canvas.

What are the common ways to show maps in SwiftUI?

Show Map in SwiftUI

What is declarative syntax?

The declarative syntax is a modern language paradigm that helps developers to write code procedurally. Using the declarative syntax developer describes the code they want to write, without having to worry about how it’s going to be shown/implemented. SwiftUI uses a declarative syntax, so you can simply state what your user interface should do. For instance: You can write that you want an image at the bottom of the screen. 

What is Dynamic replacement?

Dynamic replacement is the method by which Xcode can swap edited code directly in your live app on Canvas. The design canvas in XCode is not a dummy user interface, it’s depicted as a live app using dynamic replacement and the app is being built and run constantly when you change any part of the code in SwiftUI.

Why “Previews” are powerful than the build and run approach?

Preview is super powerful to visualise the data in different scenarios for example dark mode, localisation, font size etc. You can configure one or many previews of any SwiftUI views with sample data and you don’t need to manually run in five devices with 15 combinations. By using previews you can display your UI on any device, any orientation and any colour scheme.

What is View in SwiftUI?

A SwiftUI view is the core building block of your user interface. It conforms to the View protocol which is a type that represents part of your app’s user interface and provides modifiers that you use to configure it.

How to style a Text View in SwiftUI?

One of the most basic ways to style text in SwiftUI is by adjusting the font. The font() modifier can be used to set the font of a text view. Read more: How to style Text in SwiftUI?

Why do we need UIViewRepresentable?

UIViewRepresentable acts as a wrapper to use UIKit’s UIView in SwiftUI View. To add your view into your SwiftUI interface, create your UIViewRepresentable instance and add it to your SwiftUI interface. The system calls the methods of your representable instance at appropriate times to create and update the view.

What is a modifier in SwiftUI?

Modifiers in SwiftUI add certain enhancements to a View. SwiftUI provides hundreds of built-in modifiers eg. padding() , background() and offset(). You can also create a custom modifier that does something specific to your view. Common Use cases of ViewModifier in SwiftUI

What will happen when you add a modifier to a view? 

When you apply a modifier to a view, it will add specific behaviour to that view and return a new view.

What is ViewModifier?

ViewModifier is the protocol that helps to customise another modifier or views. You can chain multiple view modifiers and at the end, it will return another view. To enhance a UIView in a UIKit, you use the view properties. In UIKit, you probably use YourView.backgroudColor = .red to customise the UIView. It is an imperative approach to enhance your views. To customise a view in a SwiftUI declarative approach, developer just define what the view should look like using ViewModifier. Read more: Common Use cases of ViewModifier in SwiftUI

What is a custom modifier in SwiftUI?

Use of custom view modifier for reusability in SwiftUI

Best practices for writing SwiftUI code

Tips for Writing Cleaner SwiftUI code

What are the benefits of using SwiftUI?

The main benefits of SwiftUI are the followings: 

  • SwiftUI has a declarative syntax which easy to use and learn.
  • SwiftUI syntax is very simple, modern and clean.
  • SwiftUI promotes reactive programming through Binding, State and the Combine framework
  • SwiftUI provides a live preview using the canvas, an interactive interface editor. 
  • More – Top 10 Pros and Cons of SwiftUI

What are the common issues developers face when they want to adopt SwiftUI?

  • Learning curve. 
  • For complex UI, the best practices are not defined by the community yet. 
  • SwiftUI is not available for older operating systems that you want to support.
  • More – Top 10 Pros and Cons of SwiftUI

Why should you learn SwiftUI?

  • New paradigm shift.
  • UI development is super fast. 
  • Help you to learn decoupling UI from business logic.
  • Help you to understand other declarative frameworks like ReactNative, Flutter, composite layout.
  • More – Debunk SwiftUI myth – Frequently asked questions

When should you use LazyVStack or LazyHStack?

LazyVStack or LazyHStack are the stacks where the view doesn’t create items until it needs to render them onscreen.

Why ZStack is necessary?

ZStack overlays its children on top of each other. Inside the ZStack, later children appear “on top” of earlier ones. ZStack is necessary to organise the Views that overlap.

What is the difference between declarative and imperative programming or syntax?

The imperative syntax uses statements that change a program’s state. An imperative program consists of commands for the computer to perform. It focuses on describing how a program operates, by implementing algorithms in explicit steps.

On the other hand, Declarative syntax uses its desired results without explicitly listing commands that must be performed. It focuses on the what rather than on the how. In an imperative syntax, you need to provide step-by-step instructions to perform some action. In declarative programming, you only need to describe the action not how to perform the action.

Do you have some tips for writing cleaner SwiftUI code?

Tips for Writing Cleaner SwiftUI code

How is SwiftUI different from storyboards and from UiKit?

In UIKit, UIs are made using the drag-and-drop interface builder. UIKit apps connect to the code using outlets and actions. In SwiftUI, UIs are made programmatically. SwiftUI code is controlled from the same code as the UI. SwiftUI is only in iOS 13.0 and later. SwiftUI vs UIKit – Benefits and Drawbacks of SwiftUI

How does SwiftUI correlate with storyboards?

SwiftUI can be integrated with UIKit quite easily. In order to integrate SwiftUI on those frameworks, you need to use a hosting controller and can put a SwiftUI view in it. There are representable protocols (for example: UIViewRepresentable, UIViewControllerRepresentable) where you can make and update your UIKit views for SwiftUI.

SwiftUI vs UIKit

SwiftUI vs UIKit – Benefits and Drawbacks of SwiftUI

Continue with

SwiftUI Interview Questions And Answers – Part 2 – UI Advance

SwiftUI Interview Questions And Answers – Part 3 – Data

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.

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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