SwiftUI Interview Questions And Answers – Part 2 – UI Advance

Get prepared for your next SwiftUI interview with these advanced SwiftUI interview questions and answers. Covering topics such as the difference between SwiftUI and UIKit, the single source of truth principle, handling asynchronous tasks, and implementing animations, this resource will help you demonstrate your expertise in SwiftUI and stand out in the job market. Whether you are an experienced developer looking to advance your career or a beginner looking to break into the field, these SwiftUI interview questions and answers will help you showcase your skills and knowledge.

Preparing for a SwiftUI interview can be a daunting task, especially if you’re an experienced developer looking to expand your skillset or a beginner just starting out in the industry. One of the best ways to prepare is by familiarizing yourself with the most common SwiftUI interview questions and answers. This will not only help you understand the types of questions you’ll be asked, but it will also give you a better understanding of the concepts and principles that are important to the role of a SwiftUI developer. In this article, I will go through some advanced UI related topics of SwiftUI. Most of the answer needs more explanation and I will add necessary links as much as possible to understand the concept. Take a look at the first part of the series SwiftUI Interview Questions and Answers – Part 1 – UI Basics where I describe the basics of SwiftUI.

How do Views work in SwiftUI?

SwiftUI uses easy, compact, and declarative syntax for formulating a wide range of complex views which was impossible by UIKit. Every view in SwiftUI must conform to View which is an associated type. The view must have a single property called body to satisfy the conformance of the View protocol. View must provide an implementation of body which must return a type that conforms to View. This return type uses ‘some View’ which simply means the body must return some kind of a view and caller of that view does not need to know it’s type. It is very clever approach where the body will always be implementing the View protocol, but the concrete implementation type does not need to be known by the caller.

Why does SwiftUI use ‘some View’ for its view type?

The some keyword is used to describe an opaque type which was introduced in Swift 5.1. The opaque type is useful to return a type without providing the exact details on the concrete type. Generally speaking, opaque types as a kind of generic function where the placeholder types are filled by the implementation return type. The opaque type limits what callers need to know about the returned type, only exposing information about its protocol compliance. Using an opaque type is a way to let the compiler decide what would be the concrete type of a function return, based on the actual returned value, limiting the options to the types that comply to a given protocol. Returning some View means even though we don’t know what view type is going back, the compiler does.

What is the View State?

The state of a view, is the set of values of all the @State properties of a view at a given time.

How does SwiftUI render the Views?

SwiftUI is a declarative framework for building user interfaces on Apple platforms. In a declarative framework, you describe the desired end state of your user interface and the framework is responsible for rendering the views and handling user interactions.

In SwiftUI, you create views by combining simple, reusable building blocks called “view components.” These view components can be combined in a variety of ways to create more complex layouts and interactions.

When you build a SwiftUI app, you create a hierarchy of views by composing these view components and arranging them within a parent-child hierarchy. Each view in the hierarchy is responsible for rendering its own content and layout, as well as handling user interactions and responding to changes in state.

SwiftUI uses a “diffing” algorithm to determine the minimum set of changes needed to update the user interface whenever the state of your app changes. When the state of a view changes, SwiftUI compares the new and old versions of the view and determines the minimum set of changes needed to update the view. This allows SwiftUI to update the user interface efficiently, without having to rebuild the entire view hierarchy from scratch.

SwiftUI also uses a “lazy” rendering strategy, which means that it only renders views that are visible on the screen. This helps to improve performance by reducing the number of views that need to be rendered and updated at any given time.

In summary, SwiftUI renders views by building a hierarchy of view components, using a diffing algorithm to determine the minimum set of changes needed to update the user interface, and using a lazy rendering strategy to improve performance. This allows SwiftUI to provide a fast and efficient way to build and update the user interface of your app.

How do you create custom animations in SwiftUI?

To create custom animations in SwiftUI, you can use the withAnimation() function and specify the desired animation parameters, such as the duration, curve, and repetition. You can also use the animation() modifier to specify the animation for a specific view.

How do you create custom gestures in SwiftUI?

To create custom gestures in SwiftUI, you can use the Gesture protocol and implement the shouldBegin() and updating() methods. You can then attach the custom gesture to a view using the gesture() modifier.

How do you create custom transitions in SwiftUI?

To create custom transitions in SwiftUI, you can use the Transition protocol and implement the body property. You can then specify the custom transition using the transition() modifier.

How do you create custom shapes in SwiftUI?

To create custom shapes in SwiftUI, you can use the Shape protocol and implement the path() and insetPath() methods. You can then create an instance of the custom shape and use it in your views.

How do you create custom controls in SwiftUI?

To create custom controls in SwiftUI, you can create a view that conforms to the Control protocol and implement the body and controlProperties properties. You can then use the custom control in your views just like any other control.

How does SwiftUI re-render the Views?

In SwiftUI, views are automatically re-rendered whenever their state changes. This is because SwiftUI is a declarative framework, which means that you describe the desired end state of your user interface and the framework is responsible for rendering the views and handling user interactions.

When the state of a view changes, SwiftUI compares the new and old versions of the view and determines the minimum set of changes needed to update the view. This process is known as “diffing.”

To determine the minimum set of changes needed to update a view, SwiftUI compares the new and old versions of the view and looks for differences in their properties, such as their layout, content, and behavior. If any differences are found, SwiftUI updates the view to reflect the new state.

For example, if you have a view with a label that displays a piece of text, and you change the text of the label, SwiftUI will automatically re-render the label to display the new text.

What is the “single source of truth” principle in SwiftUI and why is it important?

The “single source of truth” principle in SwiftUI refers to the idea that the state of your app should be stored in a central, consistent location, rather than being scattered across multiple places in your code. This is important because it helps to ensure that your app’s state is consistent and predictable, which makes it easier to debug and maintain.

In SwiftUI, the state of your app is typically stored in a “view model” object, which is a simple, plain-old-Swift-object (POSO) that contains the data needed to render the user interface. The view model object is then passed to the view hierarchy as a dependency, and the views bind to the properties of the view model to display the data and respond to changes.

Why opaque return types are so important in SwiftUI?

Opaque return types are a feature of the Swift programming language that allow you to hide the underlying type of a value behind a “type-erased” wrapper. In SwiftUI, opaque return types are important because they allow you to create reusable view components that can be used in a variety of contexts without exposing their internal implementation.

For example, imagine that you have a view component that displays a list of items, and you want to allow users to tap on an item to select it. You could create a view component that returns a Binding<Int> to represent the selected item index, but this would limit the reuse of the view component to only situations where the selected item index is needed.

To make the view component more reusable, you can use an opaque return type to hide the underlying type of the selection. This allows you to use the view component in a variety of contexts, without exposing the internal implementation of the selection.

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.

✍️ Written by Ishtiak Ahmed

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