20 RxSwift Interview Questions and Answers

RxSwift is a popular programming language for developing iOS apps. When applying for a position in iOS development, it is likely that employers will expect you to have a strong understanding and familiarity with RxSwift. Understanding what RxSwift questions you are most likely to encounter and how to properly answer them improves your chances of making a positive impression on the hiring manager. In this article, we discuss the most commonly asked RxSwift questions and how you should respond.

RxSwift Interview Questions and Answers

Here are 20 commonly asked RxSwift interview questions and answers to prepare you for your interview:

1. What is RxSwift?

RxSwift is a reactive programming library for iOS and OS X development. RxSwift allows you to write code that is more responsive to user input and can better handle asynchronous events.

2. Can you explain what Reactive Programming means in the context of Swift and iOS development?

Reactive Programming is a programming paradigm that is based on the idea of reacting to events as they occur. In the context of Swift and iOS development, this means that developers can write code that will automatically respond to changes in data or user input. This can make code more responsive and easier to maintain.

3. Why do you think Reactive Programming is important for mobile app developers?

Reactive Programming is important for mobile app developers because it helps to manage asynchronous data streams. This is especially important in mobile apps where there are often many different data sources that need to be integrated in real-time, such as GPS data, sensor data, and user input. Reactive Programming helps to make this possible by allowing developers to declaratively specify how these data streams should interact.

4. Where can I find good documentation on how to use RxSwift? Is it possible to read and understand some example code that uses this framework?

The RxSwift website has a lot of good documentation on how to use the framework, and there are also a lot of good blog posts and articles out there that can help you understand how to use it. Additionally, there are a lot of example projects on GitHub that you can look at to see how RxSwift is used in practice.

5. How is RxSwift different from other popular reactive frameworks like ReactiveCocoa or PromisesKit?

RxSwift is different in a few key ways. First, it is built specifically for Swift, whereas the other frameworks are built for Objective-C. Second, RxSwift uses a declarative style, rather than an imperative style. This means that you describe what you want to happen, rather than telling the code how to do it step by step. Finally, RxSwift uses a functional programming approach, rather than an object-oriented approach. This means that everything is treated as a function, and you compose small functions together to create more complex ones.

6. What are the main components of RxSwift?

The main components of RxSwift are the Observable, the Observer, and the Scheduler. The Observable is the object that emits the events that will be observed. The Observer is the object that receives the events from the Observable. The Scheduler is the object that controls when the events are emitted and received.

7. Can you give me a simple example of using RxSwift with swift to perform an asynchronous operation?

Using RxSwift with swift to perform an asynchronous operation is actually quite simple. All you need to do is use the Observable type to wrap around the asynchronous operation. For example, let’s say you have an asynchronous operation that fetches data from a remote server. You would simply do the following:

Observable.create { observer in

// Fetch data from remote server asynchronously

// Once data is fetched, emit it to the observer

observer.onNext(data)

// Complete the sequence

observer.onCompleted()

return Disposables.create()

}

This will create an observable sequence that will fetch the data from the remote server and emit it to any observers.

8. What are Observables in RxSwift?

Observables are sequences that can be observed. They emit events over time, which can be anything from a single value to a complete sequence of values. When you subscribe to an Observable, you are telling it that you want to be notified of any new events that it emits.

9. What’s the difference between Single, Maybe, Completable and Driver types?

Single: Represents a stream of exactly one element.
Maybe: Represents a stream that might contain zero or one element.
Completable: Represents a stream that will emit an event exactly once, either .success or .error.
Driver: Represents a UI-driven stream that completes once the UI is unloaded.

10. Are observers in RxSwift always passive? If not, then what are active observers?

Observers in RxSwift are not always passive. Active observers are those that actively participate in the execution of the observable sequence, such as by subscribing to it. Passive observers are those that simply observe the sequence, such as by logging its events.

11. Can you give me a few examples of when it might be useful to use an active observer?

There are a few different situations where it might be useful to use an active observer. For example, if you are trying to monitor a network connection and want to be able to react immediately if the connection is lost, then using an active observer would be a good choice. Additionally, if you are trying to perform some sort of real-time data processing and need to ensure that your data is always up-to-date, then using an active observer would be beneficial.

12. What are Disposable objects?

Disposable objects are used to manage the execution of Observable sequences. When you subscribe to an Observable sequence, you return a Disposable object. This object can be used to cancel the subscription, which will stop the execution of the Observable sequence.

13. What does subscribing mean in RxSwift?

Subscribing is the process of attaching an observer to an observable sequence, in order to receive notifications of new elements emitted by that sequence.

14. What is backpressure?

Backpressure is a mechanism used to ensure that an Observable does not emit items faster than its Observer can consume them. If an Observable emits items faster than its Observer can consume them, then those items will be queued up until the Observer is ready to consume them. This can lead to memory issues if the queue gets too large, so backpressure is used to ensure that this doesn’t happen.

15. What are the different ways in which you can handle backpressure in RxSwift?

There are a few ways that you can handle backpressure in RxSwift. One way is to use the buffer operator, which will keep a certain number of items in a buffer and then emit them when the buffer is full. Another way is to use the throttle operator, which will emit items at a certain interval. Finally, you can use the window operator, which will emit items in batches.

16. Can you explain to me how hot and cold observables differ? Which one do you think is more useful?

Hot observables emit items regardless of whether or not there are any subscribers, while cold observables only emit items when there is at least one subscriber. In general, I think cold observables are more useful because they allow you to control when items are emitted, which can be helpful in terms of managing resources and avoiding potential errors.

17. What are Subjects? When should they be used?

Subjects are a type of observable that can also be used to emit values. This means that they can be used to both subscribe to values and to emit values. Subjects are usually used when you want to be able to control the order in which values are emitted. For example, you might use a subject to control the order in which values are emitted from a set of observables.

18. Does RxSwift make any guarantees about thread-safety?

No, RxSwift does not make any guarantees about thread-safety.

19. What are the common pitfalls associated with RxSwift that we should avoid?

There are a few common pitfalls associated with RxSwift that we should avoid. One is forgetting to unsubscribe from observables when we are finished with them. This can lead to memory leaks. Another is not using the correct scheduler when subscribing to observables. This can lead to race conditions. Finally, we should be careful not to create too many observables in our code. This can lead to performance issues.

20. Can you give me a real-world example of where you would have used RxSwift? What were the benefits of using this over traditional synchronous programming techniques?

I have used RxSwift in a number of projects, most recently in a project that involved fetching data from a REST API. The benefits of using RxSwift in this case were numerous. First, by using observables we were able to easily chain together a series of network requests. This would have been much more difficult to do using traditional synchronous programming techniques. Additionally, RxSwift made it easy to handle errors that might occur during the fetching of data. Finally, using RxSwift allowed us to easily update the UI in response to changes in the data.