iOS Development Interview Questions: A Comprehensive Guide

Intermediate iOS interview questions and answers

Explain the use of break statements in Swift language?

It is used in a loop when you want to end a statement immediately in a loop. Also, it is used to end the case in the switch statement. To put it simply, a break statement stops the flow of code and ends the program when a certain condition is met in a program.

What is the difference between “didSet” and “willSet” in Swift?

A property observer called “didSet” is called after the value of a property has been set. A property observer called “willSet” is called before the value of a property is set. “didSet” and “willSet” can be used to do extra things when the value of a property changes, like updating the UI or calling other methods.

It is the simplest way to store data without a database using key-value pairs. Basically, it provides a programmatic interface for interacting with the default systems. This is the default setting that lets an app change its behavior to suit a user’s tastes. For example, users can specify their preferred media playback speed.

NSUserDefaults support which types?

Types supported by NSUserDefaults are as follows.

What is the use of reuseIdentifier?

It gathers together rows that are next to each other in an UITableView. For example, rows that are only different in what they contain but have the same layout otherwise. A UITableView object keeps track of a list of the currently reusable cells, giving each one a unique reuse identifier. The delegate can access this list in the dequeueReusableCell method.

Tell one difference between viewDidLoad and viewDidAppear.

Where viewDidLoad pop-ups on the screen only when the view is loaded. You can set up any instance variables and build any views that are still on this view controller’s device at this point.

viewDidAppear appears each time on the device. From this point of view, you can do any layout tasks or drawings in the User Interface.

Through which methods can you identify the layout of elements in UIView?

InterfaceBuilder: It gives collections of user interface objects to a Swift developer.

There is a relationship between two user interface objects called NSLayoutConstraints that the constraint-based layout system has to take into account.

CGRect: CGRect is a structure that contains the location and dimensions of a rectangle.

What is the significance of “?” in Swift?

When declared, “?” makes a property optional. However, if the property is not valuable, it helps avoid runtime errors.

What do you know about synchronous and asynchronous tasks in iOS?

Synchronous tasks are those for which you have to wait to complete before moving ahead. On the contrary, for asynchronous tasks, you dont have to wait for the task to complete. Asynchronous code execution lets the thread keep running while the task is done in the background. Synchronous code execution stops the current thread until the task is finished.

What is a de-initializer, and how is it used in Swift?

A de-initializer is called before a class instance is deallocated.

To write it, we use the deinit keyword as follows:

// deinitialization is performed

Explain lazy stored properties?

These are those properties whose first values are not computed until the first time they are used. To use it, you can report the lazy modifier before its declaration.

What is the use of Size Classes?

iOS has a feature called Size Classes that lets developers make interfaces that can change to fit different screen sizes and device orientations. It is used to create user interfaces that look great and function well across different iOS devices. Developers can tell Size Classes how to change the layout and behavior of their app’s UI when it’s seen on a different device.

Can you name the JSON framework supported by iOS?

SBJson framework is a data interchange format that is easy to read and write. Here JSOn stands for JavaScript Object Notation. It’s an Objective-C JSON syntax analyzer and generator that gives you more controls and flexible APIs to make working with JSON easier. You can lower the delay seen during each download and parse cycle of documents over a slow connection with the SBJson framework. It also lets you start parsing and return chunks of the parsed document, and it can parse large documents bit by bit, so you don’t have to keep them in memory.

Explain one difference between atomic and nonatomic properties?.

While atomic properties are slow but thread-safe, only one thread is accessed by the variable(static type). It is not a keyword but a default behavior. Whereas nonatomic is fast but thread-unsafe and multiple thread access by the variable (dynamic type). It is not a default behavior; thats why we need to add the keyword in the property attribute. If two different threads access the same variable at the same time, something strange might happen.

List the different kinds of iOS Application States.

• Not running state
• Active state
• Background state
• Suspended state
• Inactive state

List the ways to achieve concurrency in iOS?

Explain SpriteKit and SceneKit.

SpriteKit is a framework to develop animated 2D objects easily. SceneKit is a framework from OS X that helps with 3D graphics design.

What is the difference between “try”, “try?”, and “try!” in Swift?

You use “try” for functions that throw errors that might happen, “try?” for functions that handle errors nicely by returning nil, and “try!” for functions that throw errors that force unwrap the result and crash the app if an error happens. The word “try?” is usually used for non-essential tasks where errors can be handled gracefully. On the other hand, “try!” should only be used when you are sure that an error won’t happen.

Explain autorelease pool in Swift.

An autorelease pool’s main job is to help programs that make a lot of short-lived objects manage their memory use and leave less of a memory footprint.

An autorelease pool is a stack-like structure that manages the release of objects. When you add an object to an autorelease pool, it’s not released right away. Instead, it’s added to a list of objects that will be released when the pool is empty.

Which API is suitable for writing test scripts to use the application’s UI elements?

UI Automation API as it initiates user interaction with the application and returns the log information.

UIKit classes are used from which application thread?

They should only be used from the main thread of the app, which is also called the main thread or UI thread. In iOS development, the main thread is in charge of updating the user interface. This includes handling user interactions, changes to the layout, and animations.

What is the difference between ‘app ID’ from ‘bundle ID’. Why are they used?

An app’s App ID is a unique number that Apple uses to find apps that were made by certain teams. It can be used to set up app groups, enable push notifications, and customize the App Store, among other things.

Bundle ID, on the other hand, is a number that the developer sets in Xcode that makes each app unique. It is used to identify the apps executable, as well as its resources and metadata.

Tell one difference between Cocoa and Cocoa Touch.

The application framework Cocoa is used to make apps for Mac OS, while the application framework Cocoa touch is used to make apps that run on iPads and iPhones (iOS).

Explain Automatic Reference Counting (ARC).

ARC, which stands for “Automatic Reference Counting,” is a way for iOS developers to automatically manage the memory of objects. It initializes and reinitializes the system resources. It is a memory management option for Objective-C provided by the Clang compiler. It automatically frees up memory when class instances don’t have strong references.

What do you know about Grand Central Dispatch in iOS?

Grand Central Dispatch (GCD) is a low-level API that allows running tasks in parallel. Also, it manages threads in the background. It has language features, system improvements, and runtime libraries that make multicore hardware in iOS better in a wide range of ways.

What is Deep linking in iOS?

It directs the user to an app instead of a website through URLs or universal links. Deep linking links to a specific piece of content within an app. The content could be a particular section of a page, a view, or a certain tab.

What is Objective-C in OS?

Apple uses Objective-C as an object-oriented programming language. This language entails the benefits of C and Smalltalk. Objective-C inherits C syntax, flow control statements, and primitive types and adds syntax for defining methods and classes.

List the important data types in Objective C.

What is the use of NotificationCenter?

Notification Center is a feature in iOS and macOS that lets you get system messages both inside and outside of apps. It shows your notifications history, allowing you to scroll back and see what you have missed. Users may choose what applications appear in Notification centers and how they are handled.

What is a Dictionary in Swift?

Dictionary in Swift is an unordered collection of items that stores items in key-value pairs. It uses a key as an identifier to store values that can be recovered through the same key. It is a list of key-value pairs that are not in any particular order. A key is a unique identifier, and a value is stored in a key.

Syntax:

var Dict_name = [KeyType: ValueType] ()

Example:

var examresult= [“Neha”: “44”, “Adil”: “56”, “Era” : “84”]

Output:

[“Neha” : “44”, “Adil” : “56”, “Era” : “84”]

Keys are “Neha,” “Adil,” “Era”

Values are “44”, “56”, “84”

What are design patterns in iOS?

It solves specific problems that might occur while designing an apps architecture. They are templates designed to make your coding easier. The most common design patterns are:

What is the completion handler?

They are functions passed as parameters to other functions. Also, they are used with asynchronous tasks. They tell when an operation has finished. It is a technique for implementing callback functionality using blocks/closures.

What are iBeacons in iOS?

New low-energy Bluetooth wireless technology lets iPhone and other iOS users get information about where their phones are. It is a small-scale network device that acts as a transmitter to detect and track smartphones.

Advanced iOS interview questions and answers

List the different Process States in iOS.

Not Running: The app is not launched or was running but was terminated by the system.

Inactive: The app is in the foreground but not receiving events. This state is typically brief as apps transition to other states.

Active: The app is in the foreground and receiving events.

Background: The app is in the background and executing code. Most apps enter this state briefly on their way to being suspended.

Suspended: The app is in the background but is not executing code. Without warning, the system can delete apps that aren’t being used at any time to make room for other apps.

How do you create a custom UIView in iOS? Provide an example.

To create a custom UIView, you need to create a subclass of UIView and implement the draw(_:) method.

Example:

What is Test-Driven Development (TDD)?

During the development process, it is used to choose the features of the software and write test cases for each one. It provides insights into both quality and design. You have to write and test each part of the test case. If it fails, you have to write new code to make it pass and make sure it is simple and free of bugs.

What is the difference between a closure and a function in Swift? Provide an example of each?

A closure is a block of code that can be passed around and run at a later time. A function, on the other hand, is a named block of code that does a specific job.

How do you implement a singleton in Swift? Provide an example?

To implement a singleton in Swift, you need to create a static instance property and a private initializer.

What are the different smart groups in Xcode?

Simple Smart Group—This simple smart group lets you sort your project by name, type, or path of a file.

This is the Simple Expression Smart Group. It lets you filter your project with a more complex expression, like “name contains ViewController and the path contains Controllers.” “.

Custom Smart Group—This smart group lets you use predicates, which are like expressions but give you more choices and freedom, to make your own filter.

What is the difference between a weak reference and a strong reference in iOS development?

A weak reference lets an object be freed when there are no more strong references to it. A strong reference keeps an object in memory until it is released. Like in the code below, the parent object has a strong reference to the child object, but the child object only has a weak reference to its parent:

It checks to see which parts of the code have been run and which ones have not when tests are run. A program with high test coverage runs more of its source code while being tested, which means it is less likely to have bugs that haven’t been found than a program with low test coverage.

How do you use a guard statement in Swift?

A guard statement tells a function or method to end early if a certain condition is not met. It is typically used to validate input parameters at the beginning of a function.

Heres an example:

What is the use of design patterns in Linux?

With the help of different templates, they solve common problems in software design and make writing code easier. Design patterns let you show an idea instead of a specific implementation. They also make code more adaptable, reusable, and easy to maintain.

List some common Cocoa Design patterns.

Some of the most commonly used Cocoa design patterns are:

Creational: Singleton—This pattern is used to make sure that a class only has one instance and can be accessed from anywhere in the world. This is useful when you need to share a resource or configuration settings throughout your application.

Behavioral: Memento—The Memento pattern is a behavioral design pattern that lets you save an object’s state outside of the application and then restore it later. The Memento pattern is often used in conjunction with the Command pattern and the Undo/Redo functionality.

Structural: Decorator – The Decorator pattern allows behavior to be added to an object without changing its structure. This is helpful when you want to give an object new features while it’s being used or when you want to make a chain of decorators that change an object’s behavior in a certain order.

Tell me about Adapter Pattern.

The Adapter Pattern is a design pattern that allows objects with incompatible interfaces to work together. It sits between two existing interfaces and changes the interface of one object into a different interface that clients expect.

This conversion allows objects with different interfaces to collaborate seamlessly. We need this when we have an Ethernet interface on one end and USB on the other.

How do you create a custom table view cell in iOS?

In iOS, you need to make a new subclass of UITableViewCell and set up the user interface elements in the cell contentView to make a custom table view cell. Here is an example of a custom table view cell:

List the APIs for battery-efficient location tracking.

Significant location changes: Users can track locations up to 1km. Region monitoring: Users can track enter/exit events within a radius equal to 100m or more. Visit events: It monitors enters/exits visit events from a place(Home/office).

What method do you prefer to cache data in memory?

There are many ways to do this, but NSCache is better than a simple dictionary because it clears the cache automatically when memory is low. NSCache will get rid of things without you having to do anything, and it will get rid of things in a smart way so that as much as possible stays cached.

Besides these features, NSCache also lets multiple threads safely access cached data, works with any keys and values, and lets you change how it works by using delegate methods. Because of these features, NSCache is a strong and adaptable caching solution that works well for many situations.

What is the difference between a delegate and a notification in iOS development?

A delegate is a design pattern that lets two objects talk to each other by sending messages straight to a delegate protocol. A notification, on the other hand, is a message that is sent to all registered observers without being directed at a specific person. In short, delegates are used for one-to-one communication, while notifications are used for one-to-many communication.

What is the difference between the “frame” and “bounds” properties of a UIView in iOS?

A UIView’s “frame” property tells you where it is and how big it is in relation to its parent view, while its “bounds” property tells you where it is and how big it is in relation to its own coordinate system. That is, the frame looks at where the view is in its larger view, while the bounds only look at where the view is in its own coordinate space.

What is the use of computed properties?

You can set a property whose value is computed instead of being stored with computed properties. A computed property doesn’t store a value directly in memory; instead, it figures out its value on the fly based on logic or other properties.

What is dynamic dispatch?

It is a way for the program to choose which version of a method or function to call while it is running. Dynamic dispatch lets new subclasses override methods inherited from their parent classes and provide their own implementations. This gives a program flexibility and the ability to grow.

What are the different kinds of operations possible on semaphore?

Two atomic operations are possible:

Wait(): This operation decreases the value of the semaphore by 1. If the semaphore value is already 0, the process that is waiting can’t do anything else until the value of the semaphore goes above 0.

Signal(): This operation increases the value of the semaphore by 1. One of the processes that was blocked on this semaphore because of a wait operation is now free to move.

RTOS stands for Real-Time Operating System and it is used for real-time applications. It works well for situations where a lot of events, mostly outside the computer system, need to be handled quickly and data needs to be processed within a certain time frame. With the help of RTOS, you can measure the processing time in tenths of seconds.

What is the purpose of the “prepareForReuse” method in a UITableViewCell in iOS?

A UITableViewCell’s “prepareForReuse” method is called right before it is used for a new row in the table view. It allows the cell to reset its state and prepare for new content. For example, you might reset the cells text and properties and cancel any pending network requests.

List two types of process synchronization.

The two types of process synchronization are:

Interprocess Communication (IPC): This mechanism allows processes to communicate and synchronize their actions with each other. Examples of IPC mechanisms include shared memory, message passing, and semaphores.

Mutual Exclusion, or Mutex, is a way to make sure that only one process at a time can access a shared resource or a key piece of code. Mutex can be implemented using binary semaphores, locks, or synchronization primitives.

When would you say that an app is not running?

Either when it is not launched or when it gets terminated by the system when running. The OS may have terminated the app. This means that an app is in the “Not Running” state if it can’t be seen on the screen or in the background.

When will you assume an app to be in an active state?

The app is receiving events and running code in the background, but only for a short time (in iOS 12, the app only works for 180 seconds). After that, the operating system puts the app in a suspended state and stops running code.

Can you say something about how the app transitions when launched?

After moving from an inactive state, it first goes to an active or background state. It is not said to be running before launch. The app runs in the foreground but does not receive events in an inactive state. The next stage is an active state where an application runs in the foreground and receives events. Next is the background state, where the application runs in the background and executes code. The last state is “suspended,” which means the app is running in the background but no code is being run.

Which state does an app reach briefly before being suspended?

A background state is where most apps enter briefly on their way to being suspended. Although, an application that requests extra execution time may remain in this state for a certain period. Not only does an application start up in the background, it also goes into the background state instead of the inactive state.

Can you tell the difference between == and ===?

The equal-to operator (==) checks if the values are the same. The strict equality operator (===) checks if the references point to the same file. The strict equality === operator compares the values and data types of the operands, while the equal-to == operator changes the types of the operands before comparing them.

When will you use deinit?

You can use it if you want to clean up before deallocating the class instances. With it, you can free up the memory space occupied by the system. If we manually want to deallocate instances, we only use deinit in Swift. Otherwise, Swift automatically does the deallocation. Each class contains only a single deinit.

What methods will you use to reduce the size of the App?

Bitcode: This is a representation of your app’s compiled code that Apple can change to work with different devices and architectures. This can help reduce the overall size of your app.

App slicing: This method downloads only the assets that are needed to a user’s device. It can help your app be smaller by removing assets that aren’t needed on certain devices.

On-demand resources: This method involves delivering content only when its needed. This way, users won’t have to download all of your app’s assets at once, which can help your app’s initial download size.

App thinning is a set of techniques used to make the installation process better and cut down on the space your app needs. App thinning includes techniques such as app slicing, on-demand resources, and bitcode.

Find and get rid of unused assets: Looking over your app for unused assets and getting rid of them can help your app be smaller overall.

Which of viewDidLoad and viewDidAppear will you pick to load data from a remote server and show it in the view?

It solely depends on the data use case. We can load data in viewDidLoad and cache it if it is static, doesn’t change, and is only called once. In viewDidAppear, we can load new data if the old data changes. This method is called several times during a view controller’s lifetime. viewDidLoad is called when the view controller is loaded into memory for the first time, and viewDidAppear is called when the view is visible.

Determine the value of “u” in the Swift code below.

What is the difference between a synchronous and asynchronous NSURLSession in iOS?

An asynchronous NSURLSession lets the network request run in the background without stopping the main thread, while a synchronous NSURLSession stops the current thread until the request is finished. When you need to make a quick network request that needs to block the main thread, you should use synchronous NSURLSessions. Asynchronous NSURLSessions are used for long-running network requests.

Write a code to swap two numbers?

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