Top iOS Interview Questions and How to Ace the Interview

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. For easy understanding, 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 its own 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. When an app is used on a different device, Size Classes let developers tell the app’s UI how to change its layout and behavior.

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. Usually, “try?” is used for non-essential tasks where errors can be handled gracefully. “Try!” on the other hand, 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.

Basic iOS interview questions and answers

CoreData is used as a framework for managing object graphs. It helps manage a graph of object instances that is potentially very large. By moving objects in and out of memory as needed, this lets the app use a graph that wouldn’t fit all the way in memory. CoreData also helps in managing the limitations on properties and relationships and in maintaining the integrity of references. When objects are added to or taken away from a relationship, the forward and backward links stay the same. Therefore, CoreData is considered to be the perfect framework for creating the “model” of an MVC architecture.

CoreData uses SQLite for disk storage to implement graph management. Graph management can be done with any other relational database or even a non-relational database like CouchDB. CoreData is more of an API that abstracts from the actual datastore than a database engine. You can tell CoreData how to store itself, whether it should be in a plist file, an SQLite database, a binary file, or a custom data store type.

An in-depth answer to this kind of iOS interview question is fine, but your answer will be even better if you add your own thoughts to it.

What is the difference between copy and retain?

Generally, retaining an object increases its retain count by one. This helps retain the object in memory instead of being blown away. So, if you only have the retained version of an object, you will give that copy to the person who sent it to you.

Copying an object, on the other hand, creates an extra copy or a duplicate version of the object. You give the person who sent you the object the original, but not the copied or duplicate copy.

Talk about code signing for iOS apps.

A signed application helps the system figure out who signed it and makes sure that no changes were made to it after it was signed. This is a necessary step to submit the application to the App Store for iOS and Mac. OS X and iOS both have a process for checking signatures to make sure that apps don’t run with bad signatures. Users can trust the app more because they know it was signed by a real Apple source and hasn’t been changed since it was signed.

During the build process, your digital identity is used by Xcode to sign your application. The digital identity comprises a public-private key pair and a certificate. The cryptographic functions use the private key to create the signature. Apple issues the certificate that contains the public key and helps identify you as the key pair owner.

When the executable code of an application changes in any way, the signature is no longer valid. This is how the signature protects the executable code. However, changes to s or nib files do not invalidate the signatures as these resources are not signed.

A digital identity that is different from the one that signed an application can be used to sign it again. For example, all applications on App Store are re-signed by Apple when they are sold.

For this kind of iOS interview question, it might be helpful to add if you have worked on a project with similar needs before, in this case code-signing for iOS apps.

What are the different iOS App States?

There are five app states in iOS. The OS controls the app’s state, but the app itself controls the important tasks that make crossing between states smooth. The iOS programming guide lists the five iOS app states as follows:

• Non-running: When the app is not running
• Inactive: The app is running in the background but doesn’t get any events. This can happen in an iOS app when it gets a call or SMS or when another function takes over.
• Active: The app is in this state when it is running in the foreground and getting events.
• When the app runs in the background and code is being run at the same time.
• Though the app is running in the background, it doesn’t run any code at this time.

It’s common in iOS interviews to be asked questions like the ones above, where you need to talk about more than one state or step.

Mention the main features of Swift. Also, outline its advantages and disadvantages.

The main features of Swift are as follows:

• Generics
• Optionals
• Reference types
• Value types
• Static typing
• Protocols

The biggest feature of Swift is that it is a strongly-typed language. Being a strongly-typed language is an advantage as well as a disadvantage. Development in Swift is easy because of protocols, generics, and optionals which exist because of static typing. There are some compilation errors and warnings that come up with static timing, but it also provides more security at runtime and helps with determinism for optionals, generics, and other things. This is, therefore, a big advantage of Swift. The security offered by strict type is most useful under the following circumstances:

• When making a client application, strict clarity is more important than adaptability and changeability
• When you need to put limits on developers because you don’t want them to have too much power and hurt themselves or their work
• You can use the compiler to help you write proper code when your code needs to be refactored.

All the above are scenariOS where developers build customer-facing iOS applications. One problem with Swift is that it can be too rigid, especially if the app you’re making needs to be able to change. For example, when you build a library or a framework, it needs to be flexible and dynamic. In this case, Objective-C, which supports meta-programming, might be a better choice than Swift. However, Objective-C seems to be becoming less useful right now.

MVC stands for Model View Controller. It is Apple’s main software design pattern for developing iOS apps. Models represent the data for the application. Views bring things to the screen. Controllers are used to manage the flow of data between model and view. There is no direct communication between model and view, all communication is taken care of by the controller.

As a senior developer, you should know that MVC is good for every kind of design, but it can only be used for the view layer. Because of this, using only MVC will limit the app’s architecture and could also cause the “Massive View Controller” problem.

Huge View Controller is the state of the codebase when too much logic and responsibility are given to View Controllers that aren’t supposed to have them. As a result, the code may become rigid, bloated, and difficult to alter. As a remedy, one can use design patterns such as Coordinator, MVP, and MVVM. Architectures like VIPER and RIBs can be used to make the iOS code bigger and avoid this kind of problem.

Can you differentiate between delegate and KVO?

Both, delegate and KVO, create relationships between objects. By delegating, one object takes on the role of the delegate protocol and lets another object send messages to the first object using methods defined by the protocol. When KVO is used, on the other hand, a message is sent by one object to many others, and at least some of those objects receive the message and act on it. KVO is not protocol-dependent.

As you get ready for your iOS interview, make sure you go over all the ideas where you might be asked to tell the difference between two things.

Mention some design patterns apart from the common Cocoa patterns.

In addition to the MVC, Singleton, Observer, and Delegate patterns that are often used, the following patterns can also be used to make iOS apps:

• Factory Method: This method can be used instead of class constructors to hide and abstract away the initialization of objects. The type is determined when the application is run. The switch/if statements that help figure out which objects to create instances for are also hidden and kept inside this method.
• Adapter: The Adapter design pattern lets you change the interface of one object to work with another. When you need to use something with an API that isn’t easy to work with or doesn’t work with third-party code, this is a useful tool.
• Decoration: The Decoration is a wrapper that can be put around other classes to make them better. One can wrap it around things one wants to decorate. Once it’s wrapped, it either changes and improves the objects underneath or gives them its own implementation of the interface. It also passes on the messages that were sent to it.
• Command: The Command design pattern lets you create an object that stands for an action you want to take. The operation you want to run might have its own state and rules for how to do the job. As a benefit, you can hide the operation’s internal implementation from users, give them the ability to undo or redo actions, and even run operations after they were created instead of when they were first created.
• Template: The Template design pattern has a base class that describes how to do what needs to be done. There are several abstract methods of the base class. The concrete classes that are based on the base class must implement these functions. These abstract methods are also referred to as hook methods. Users of the Template Method class talk to each other through the base class that implements the algorithm steps. The subclasses supply the concrete implementations for those steps.

Mention different options for implementing storage and persistence in iOS.

Outlined below are the ways to store data in simple to complex order:

• We can use in-memory arrays, dictionaries, sets, and other data structures to store data that doesn’t need to be kept for a long time or for short periods of time.
• For simple key-value storage, we can use NSUserDefaults/Keychain. One of these things is not safe, while the other is safe.
• We can use NSFileManager to write data to or read data from a disk. We can use File or Disk storage for data that is serialized or not that is serialized.
• Work with databases can be made easier with frameworks like Core Data and Realm.
• It is recommended to use the SQLite relational database when you need to set up complex querying mechanisms.

The iOS question above is an example of a question where the traditional answer outline above will work. However, you may get the interviewer’s attention if you add examples of how you have used any or all of the above options.

When must you use strong, weak, and unowned references?

When you work with Structs or Enums, ARC doesn’t manage these memory types. Because of this, you don’t have to say whether you are using weak or unowned references for the variables or constants there. You can use strong references in hierarchical relationships where the parent talks about the child but not the other way around. In most cases, anyway, strong references are apt. But if the relationship between two instances isn’t required, you need to make sure that one instance is weakly linked to the other. One variable must depend on another when one instance is linked to another in a way that makes it impossible for one to exist without the other. So, the instance that has to depend on the other one must have an unowned reference to the other one.

What programming language is used for iOS development?

The primary programming language used for iOS development is Swift. Objective-C is also used, but its usage has been declining in favor of Swift.

Operating systems use overlays to let programs use more memory than they would be able to otherwise.

When a program is loaded into memory, it takes up a certain amount of space. If the program is too big and needs more memory than is available, overlays can be used to only load the parts of the program that are needed at the moment. As the program executes, different portions can be swapped in and out of memory as needed.

List some important features of Swift.

Some of the important features of Swift include:

• Safety
• Simplicity in syntax
• Readability
• Support for multiplatform

Explain conditional conformances in Swift?

Without certain conditions, you can say that a generic type in Swift does not follow a protocol. This is called conditional conformance. This means that a type will only follow a protocol if certain conditions are met, like the generic parameter of the type meeting certain requirements.

Explain ButtonStyle protocol in Swift.

ButtonStyle protocol allow to customize new button styles that can be reused without the need for new views. Using this protocol, you can create a button that will appear the way you want. You will make your own style that sets a decent background for a button. You can use the buttonStyle(_:) modifier.

Tell one difference between an array and a set.

Where arrays are an ordered collection of values, sets are an unordered collection. Also, an array can duplicate elements, while a set cannot.

Explain tuples and their use in Swift.

A tuple is a set of multiple values inside Swift. They occupy space between dictionaries and structures and return values from a function call.

What is the use of GeometryReader?

GeometryReader reads all the size and position information and passes that information to its child views via GeometryProxy. It is a flexible view and takes over all the available space provided by the parent view.

Explain the bounding box.

A bounding box is a rectangle that looks like the smallest rectangle that can completely surround an object or shape. This object can be an , a text character, or any other graphical element on the screen. The bounding box is defined by its position and size. The top left corner of the rectangle’s coordinates tell you where it is, and the rectangle’s width and height tell you how big it is.

What purpose does IBDesignable serve?

When a custom view is set to IBDesignable, it allows Xcode to preview it while storyboards are edited. Interface Builder helps directly with making custom layouts. You can easily change the border color, shadow color, shadow width, border color, corner radius, and shadow opacity.

Can you tell the type of settings that are stored in your Info. plist file?

It stores those settings that must be available even when the app is not running. It is a file in the Mac and GNUstep environments that stores user settings. There are three formats plist, Text, Binary, and XML. A plist can store string, number, data(binary data), boolean, dictionary(associative array), and array.

Explain raw strings in Swift.

They make strings that print what you see, while other escape orders change the way your string prints. Raw strings are denoted by the # hash symbol, also known as pound symbol. It is used before and after quotation marks by using # at the starting and ending point.

Through what observable objects announce modifications to SwiftUI?

Using two primary ways @Published property wrapper or calling objectwillchange. send()

@Published property wrapper: It is very useful in SwiftUI. It allows us to create observable objects that automatically announce when changes occur.

Objectwillchange: It is a property defined on the ObservableObject protocol. The compiler creates a default implementation for any @Published property that changes on an object and sends out a value.

Tell me about circular references in Swift.

When two objects strongly refer each other, they can never be deallocated. And this strong reference also enables them to keep each other alive. When two objects have strong references to each other, it means that each object strongly owns the other object. This creates a cycle, which is called a circular reference.

Can we add a stored property to type through an extension?

No, we cannot add a stored property to a type through an extension in Swift.

In Swift, extensions can add initializers, instance methods, class methods, computed properties, but not stored properties. This is because stored properties need to be set up when a new instance of the type is made, and extensions can’t add their own initializers.

What do you understand about Half Open Range Operators in Swift?

It specifies a range between values x and y (x. How does using child view controllers help? One way that using child view controllers helps is by making it easier to separate and organize code in an iOS app. It is easier to understand and keep up with the codebase when a big, complicated view controller is broken up into smaller, easier-to-handle child view controllers. What are reference types?A reference type contains the location in the memory where data lives. A function is given a reference type. Instead of making a new copy of the object, it just makes another reference to it, which is shared by all the references. Tell me about Nested Function in Swift. In Swift, a nested function is a function defined within the body of another function. Nested functions are useful for organizing code and encapsulating functionality within a larger function scope. When you use nested functions, you can hide complicated logic or divide big functions into smaller, easier-to-handle pieces. What is Regular Expression?They are special string patterns that tell how to search for a string. It’s a string of characters that tells the computer what to look for in the text; it finds strings or finds and replaces strings. What is a Responder Chain?It is an order of objects that receive the chance to respond to events. It is the series of events that happen once we start interacting with the application on iOS. Applications receive and handle events using responder objects. List the different types of literals Swift has. Octal LiteralsHexadecimal LiteralsBinary LiteralsDecimal LiteralsIt provides tools and resources to steer business processes toward better performance. It is an execution unit in which a program operates. It makes sure that each program and process gets enough time on the processor to work properly and frees up time when a process is done. Name different types of control transfer statements used in Swift. List two types of classes in Swift. Subclass: It is the act of constructing a new class on an existing class. They inherit characteristics from the existing class, and you can further modify them with new characteristics. Super Class: A class that takes properties from another class is called a superclass, and the class that it takes properties from is called a subclass. What is Process management in iOS?Each thread in iOS serves as a single path of execution. Every application in IOS starts with a single thread that runs the applications main functions. How do I write a comment in Swift? For a single-line comment, I use double slashes (//), and for a comment with more than one line, I use a forward slash followed by an asterisk (/*). How do I write an optional chain in Swift? It is a process of querying and calling properties. Different queries can be chained here, but the chain fails if any link is nil. In Swift, inheritance is the process by which one class takes on the properties, methods, or other features of another class. What do you know about it? It is a fundamental behavior that differentiates classes from other types in Swift. We can write different implementations while maintaining the same behaviors by reusing code we have already written. Could you explain how to use Switch Statements in Swift? They are used instead of long if-else-if statements. It lets you inspect a value and match it with a number of cases. It works especially well for quickly making choices based on one variable that can have more than one value. Using the switch statement often results in more concise code thats easier to read.

iOS Development Interview Questions | iOS Development for Senior Developers

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