60+ Senior IOS Developer Interview Questions and Answers

System design for a food delivery app like Zomato

• Identify user roles: customers, restaurants, delivery partners

• Design a database schema to store user information, orders, menus, etc.

• Implement a search feature to find restaurants based on location, cuisine, etc.

• Integrate payment gateway for secure transactions

• Develop a user-friendly interface for placing orders and tracking delivery status

• Implement push notifications for order updates and promotions

• Ensure scalability and relia...read more

State object is a specific instance of a state, while state is a general concept representing the condition of a system.

• State object is a concrete representation of a state in a program, containing specific values and properties.

• State is an abstract concept that defines the overall condition or status of a system.

• In iOS development, state object could refer to an instance of a class representing the current state of a view or component.

• State, on the other hand, could refer to...read more

UITableView for displaying data in a list format, UICollectionView for displaying data in a grid or custom layout.

• Use UITableView for displaying data in a list format, such as a contact list or a news feed.

• Use UICollectionView for displaying data in a grid or custom layout, such as a photo gallery or a calendar.

• UITableView is simpler to implement and more efficient for displaying large amounts of data.

• UICollectionView offers more flexibility in terms of layout and customizati...read more

Grand Central Dispatch is a technology used in iOS and macOS to manage concurrent operations by allowing tasks to be executed concurrently and efficiently.

• Grand Central Dispatch (GCD) is a low-level API for managing concurrent operations.

• It allows tasks to be executed concurrently on multicore hardware.

• GCD automatically manages the execution of tasks and optimizes performance.

• GCD provides dispatch queues to manage tasks, including serial and concurrent queues.

• Example: dispatc...read more

Debouncing technique in Swift is used to limit the rate at which a function is called, preventing it from being called multiple times in a short period.

• Debouncing involves setting a time threshold and only allowing the function to be called after that threshold has passed without any new calls.

• It is commonly used in scenarios like search bars or buttons to prevent rapid firing of events.

• Example: Implementing a search functionality where the search query is only executed after...read more

Static variables in Swift are used when you want to maintain a single instance of a variable across all instances of a class or struct.

• Used to store values that are common to all instances of a class or struct

• Can be accessed without creating an instance of the class or struct

• Helpful for maintaining state across multiple instances

Answers to questions related to IOS development concepts.

• Delegate and protocol are used for communication between objects in IOS. Delegate is a design pattern that allows one object to send messages to another object when a specific event occurs. Protocol is a set of methods that a class can implement to provide a specific behavior.

• MVC is a design pattern used in IOS development. It separates the application into three components: Model, View, and Controller. Model represents...read more

I have worked on MVVM architecture in my previous project.

• MVVM stands for Model-View-ViewModel.

• It separates the UI logic from the business logic.

• The View interacts with the ViewModel, which in turn interacts with the Model.

• I used RxSwift for binding the ViewModel and View in my previous project.

Real time data in mobile apps can be handled using technologies like WebSockets, Firebase Realtime Database, or Push Notifications.

• Use WebSockets for bidirectional communication between client and server.

• Utilize Firebase Realtime Database for syncing data in real time across devices.

• Implement Push Notifications to notify users of real time updates even when the app is not open.

Collections are data structures that store and organize multiple objects or values.

• Collections are used to group related data together.

• They provide methods for adding, removing, and accessing elements.

• Examples of collections in iOS include arrays, sets, and dictionaries.

To fix a crash in an application, identify the root cause, analyze crash logs, use debugging tools, and test the fix thoroughly.

• Identify the root cause of the crash by analyzing crash logs and user reports.

• Use debugging tools like Xcode's debugger or third-party tools like Crashlytics.

• Implement defensive coding practices to handle edge cases and prevent crashes.

• Test the fix thoroughly on different devices and iOS versions to ensure stability.

• Consider using automated testing t...read more

A protocol extension allows adding functionality to existing types without modifying their original implementation.

• Define a protocol with required methods

• Create an extension for the protocol

• Implement the methods in the extension

MVVM is a design pattern that separates the UI from the business logic by introducing a middle layer called ViewModel.

• Model-View-ViewModel design pattern

• ViewModel acts as a link between the Model and View

• Data binding is used to connect the ViewModel to the View

• Updates in the ViewModel automatically reflect in the View

Lazy property delays the initialization of a property until it is accessed for the first time.

• Lazy properties are useful when the initialization of a property is expensive and not always needed.

• They can improve performance and memory usage by delaying the initialization until it is actually needed.

• They are declared using the 'lazy' keyword and must be variables, not constants.

• Example: lazy var myProperty = expensiveInitialization()

• Lazy properties are thread-safe by default in...read more

Memory leak is a situation where a program fails to release memory it has allocated, leading to a gradual loss of available memory.

• Memory leaks occur when a program allocates memory but does not free it after use.

• Common causes of memory leaks include not deallocating memory after use, retaining references to objects unnecessarily, and circular references.

• To solve memory leaks, developers can use tools like Instruments to identify leaks, analyze code for potential issues, and ...read more

OOPS stands for Object-Oriented Programming System. There are four main types of OOPS concepts: Inheritance, Encapsulation, Polymorphism, and Abstraction.

• Inheritance: Allows a class to inherit properties and behavior from another class. Example: class B extends class A.

• Encapsulation: Bundling data and methods that operate on the data into a single unit. Example: private variables in a class.

• Polymorphism: Ability to present the same interface for different data types. Example:...read more

Delegates are used in iOS development to allow one object to communicate with another object.

• Delegates are used to establish communication between objects in iOS development.

• Delegates are defined using protocols in Swift or Objective-C.

• An example of using delegates is implementing the UITableViewDelegate protocol to handle table view events.

My capabilities align with the current project requirements, including expertise in Swift, Objective-C, and experience with integrating third-party libraries.

• Proficient in Swift and Objective-C programming languages

• Experience with integrating third-party libraries and APIs

• Strong understanding of iOS design patterns and best practices

Use localization files to support multiple languages in iOS apps

• Create a Localizable.strings file for each language you want to support

• Use NSLocalizedString function to retrieve localized strings in code

• Update UI elements with localized strings in Interface Builder

• Test the app with different language settings to ensure proper localization

Delegate is a design pattern in iOS development where one object acts on behalf of, or in coordination with, another object.

• Delegates are used to establish communication between objects.

• Delegates help in implementing the concept of loose coupling.

• Delegates are commonly used in iOS development for handling events, data passing, and customizing behavior.

• Example: UITableViewDelegate and UITableViewDataSource protocols in UITableView where the delegate object handles table view e...read more

Adopting new iOS versions involves staying updated, testing compatibility, updating codebase, and utilizing new features.

• Stay updated on new iOS versions and features released by Apple.

• Test compatibility of existing apps with the new iOS version.

• Update the codebase to ensure compatibility and take advantage of new features.

• Utilize new features introduced in the latest iOS version to enhance app functionality.

• Consider redesigning UI/UX to align with the latest iOS design guide...read more

Replace a string in an array at a given index

• Create an array of strings

• Use the index provided to replace the string at that index

• Ensure the index is within the bounds of the array

Bounds refer to the content area of a view, while frame refers to the position and size of a view within its superview.

• Bounds are relative to the view's own coordinate system, while frame is relative to its superview's coordinate system.

• Changing the bounds of a view affects the position and size of its subviews, while changing the frame affects the position and size of the view itself.

• For example, if a view has a frame of (10, 10, 100, 100) and a bounds of (0, 0, 80, 80), the...read more

Classes are reference types, structs are value types. GCD is low-level API, Operation queue is high-level API for concurrency.

• Classes are reference types, stored on the heap. Structs are value types, stored on the stack.

• GCD is a low-level API for managing concurrent operations. Operation queue is a high-level API built on top of GCD.

• GCD provides a simple and efficient API for dispatching tasks to a queue. Operation queue adds additional features like dependencies and cancella...read more

Button hierarchy in Objective-C refers to the order in which buttons are arranged and displayed on the user interface.

• Button hierarchy determines the visual layout and organization of buttons on a screen.

• Buttons can be arranged in a linear or hierarchical manner.

• The hierarchy can be defined using constraints or by using a layout manager.

• Example: A login screen may have a primary button at the bottom and secondary buttons above it.

Circular reference cycle occurs when two or more objects reference each other, creating an infinite loop.

• Circular reference cycle can lead to memory leaks as the objects involved will never be deallocated.

• To prevent circular reference cycles, weak references can be used in one of the objects.

• Example: Object A has a strong reference to Object B, and Object B has a strong reference to Object A, creating a circular reference cycle.

Calculate electricity bill using algorithm

• Calculate total units consumed

• Apply tariff rates based on consumption slabs

• Add fixed charges and taxes to get final bill amount

SOLID principles are a set of five design principles that help make software designs more understandable, flexible, and maintainable.

• Single Responsibility Principle (SRP) - A class should have only one reason to change.

• Open/Closed Principle (OCP) - Software entities should be open for extension but closed for modification.

• Liskov Substitution Principle (LSP) - Objects of a superclass should be replaceable with objects of its subclasses without affecting the functionality.

• Inter...read more

Iterate through the array to find the second largest number.

• Sort the array in descending order and return the second element.

• Initialize two variables to keep track of the largest and second largest numbers while iterating through the array.

• If the array contains duplicates, consider whether to include them in the comparison for the second largest number.

Memory management in iOS is handled through Automatic Reference Counting (ARC) which automatically manages memory by keeping track of object references.

• ARC automatically adds and removes object references as needed to manage memory

• Weak references are used to prevent retain cycles and memory leaks

• Delegates and closures can create strong reference cycles if not managed properly

Access control refers to the process of restricting or granting access to resources based on user identity and permissions.

• Role-based access control (RBAC) - access is granted based on the user's role within an organization

• Attribute-based access control (ABAC) - access is granted based on specific attributes of the user, such as job title or department

• Discretionary access control (DAC) - access is granted at the discretion of the resource owner

• Mandatory access control (MAC) -...read more

MVVM (Model-View-ViewModel) is a design pattern used in Swift to separate the user interface logic from the business logic.

• MVVM divides the code into three main components: Model, View, and ViewModel.

• Model represents the data and business logic of the application.

• View displays the data and interacts with the user.

• ViewModel acts as a mediator between the Model and View, handling the logic for the View.

• MVVM helps in making the code more modular, testable, and maintainable.

SSL pinning is a security measure used to prevent man-in-the-middle attacks by validating the server's SSL certificate.

• Implement SSL pinning by embedding the server's SSL certificate within the app's code.

• During the SSL handshake, compare the server's certificate with the embedded certificate to ensure they match.

• If the certificates match, the connection is considered secure and the data exchange can proceed.

• SSL pinning helps protect against attacks where a malicious actor tr...read more

Use XOR operation to swap two variables without a third one

• Use XOR operation to swap two variables without a third one

• Example: a = 5, b = 10. a = a XOR b, b = a XOR b, a = a XOR b. Now a = 10, b = 5

Dispatch Group is a mechanism in iOS for managing multiple tasks and synchronizing their completion.

• Dispatch Group allows you to monitor a group of tasks and be notified when they are all completed.

• You can use Dispatch Group to wait for multiple asynchronous tasks to finish before proceeding.

• Dispatch Group can be used to manage concurrent tasks and avoid race conditions.

• Example: Using Dispatch Group to download multiple images concurrently and updating UI when all downloads a...read more

OOPS (Object-Oriented Programming) is a programming paradigm based on the concept of objects, which can contain data and code.

• OOPS focuses on the following concepts: Inheritance, Encapsulation, Polymorphism, and Abstraction.

• Inheritance allows a class to inherit properties and behavior from another class.

• Encapsulation refers to the bundling of data with the methods that operate on that data.

• Polymorphism allows objects of different classes to be treated as objects of a common s...read more

Objective-C is a superset of C with object-oriented features, while Swift is a modern, safer, and more concise programming language developed by Apple.

• Objective-C is a superset of C with object-oriented features

• Swift is a modern, safer, and more concise programming language

• Objective-C uses square brackets for method calls, while Swift uses dot notation

• Swift has optionals to handle nil values safely, while Objective-C uses nil pointers

• Swift has type inference, making code clea...read more

Sorting and searching algorithms are essential for efficient data manipulation and retrieval.

• Sorting algorithms like quicksort, mergesort, and heapsort rearrange elements in a specific order.

• Searching algorithms like binary search and linear search help find specific elements in a dataset.

• Efficient algorithms can significantly improve performance in large datasets.

Multithreading is the ability of a CPU to execute multiple threads concurrently, allowing for improved performance and responsiveness in applications.

• Multithreading allows multiple tasks to be executed simultaneously on a single CPU core.

• It can improve performance by utilizing idle CPU time for other tasks.

• Examples include running background tasks while the main thread handles user interactions in an iOS app.

Structs are value types and passed by value, while classes are reference types and passed by reference.

• Structs are used for small, simple data types like coordinates or colors.

• Classes are used for more complex data types that require inheritance or reference semantics.

• Structs are copied when passed around, while classes are passed by reference.

• Structs are stack allocated, while classes are heap allocated.

SSL pinning is a security measure to prevent man-in-the-middle attacks by associating a specific SSL certificate with a particular app.

• Implementing SSL pinning using public key

• Implementing SSL pinning using certificate

• Implementing SSL pinning using hash of certificate

let is used to declare a constant while var is used to declare a variable.

• let is immutable while var is mutable

• let can only be assigned once while var can be assigned multiple times

• let is preferred over var for safety and performance reasons

iOS architecture refers to the overall structure and design of an iOS application, including how components interact and communicate with each other.

• iOS architecture typically includes components such as Model-View-Controller (MVC), Model-View-ViewModel (MVVM), and Model-View-Presenter (MVP).

• Architectural patterns help in organizing code, improving scalability, and enhancing maintainability of iOS applications.

• Examples of iOS architectural patterns include VIPER (View, Intera...read more

Delegate methods of URL session are used to handle various events during network requests.

• Delegate methods are used to handle authentication challenges, background session events, and data tasks.

• Examples include URLSessionDelegate, URLSessionDataDelegate, URLSessionTaskDelegate.

• Delegate methods can be used to handle redirects, caching policies, and response validation.

Optional is a type in Swift that represents a value that may or may not exist.

• Optional is used to handle situations where a value may be missing or not yet available.

• Optional variables can either have a value or be nil.

• Optional unwrapping is used to safely access the value of an optional variable.

MVC focuses on separating data, presentation, and logic. MVVM adds a ViewModel to handle communication between Model and View.

• MVC stands for Model-View-Controller, where Model represents data, View represents UI, and Controller handles user input and updates the Model and View accordingly.

• MVVM stands for Model-View-ViewModel, where ViewModel acts as an intermediary between Model and View, handling data binding and communication.

• In MVC, the View directly interacts with the Mod...read more

MVC is a design pattern that separates an application into three interconnected components: Model, View, and Controller.

• Model represents the data and business logic of the application

• View is responsible for displaying the data to the user

• Controller acts as an intermediary between the Model and View, handling user input and updating the Model and View accordingly

• MVC promotes separation of concerns and modularity, making it easier to maintain and modify the application

• Example: ...read more