Best iOS Interview Questions And Answers

We all know interviews can be stressful - it doesn't matter if this is your first interview in life or if you are a seasoned developer with several years of development under your belt.

As a conversation partner, you need to be willing to present yourself in a good light, which is really difficult to do within an hour or so of the conversation. We, as developers, usually don't want to memorize documentation and even just google it. It's okay, though. Nobody expects us to remember everything ... unless it's an interview.

This may not be so easy for the interviewer, either. You want to hire someone for your company who fits well with your team, and you don't have much time to get to know that person. You need to know what to ask about and how to behave - you don't want the other person to feel uncomfortable, as this could lead to judging someone wrong and missing out on a great developer.

To a large extent, both parties need to prepare for the iOS developer interview questions, and we hope that our page with advanced iOS interview questions and answers will help you prepare a little better for future interviews.

Junior iOS Developer Interview Questions


What's Swift? Explain some of the features.

Swift, a modern programming language, was announced by Apple Inc. in June 2014.

  • Fast (static method dispatch)
  • Safe (type safe)
  • Friendly syntax (more concise than objective-c)

Some key features are unique and powerful: generics, tuples, closures, and type inference are optional.


What is the difference between static typing and dynamic typing?

Swift uses static typing, which can lead to a compiler error. Objective-C uses dynamic typing, which performs type checking at runtime. This means that the code can compile even if it contains errors that prevent the script from working properly.


What is type inference?

A function that allows the compiler to automatically set the data type of a variable without setting the data type by looking at the value.


What are generics?

A type that can take any type. It is type safe, which means the compiler will complain at compile time. For example, if you pass a string as a generic type and use it as an integer, a compile-time error occurs. This is good because you can spot errors ahead of time.


Can objects be nil in Objective-c and Swift?

In Objective-c, any object can be nil. In Swift, only Optionals can be null.


What are protocols?

A protocol is an interface, that is, it contains abstract methods, constants, and variables. Protocols provide shared functionality between classes. You can implement multiple protocols.


How is volatility achieved in Swift and Objective-c?

In Swift, a constant is a constant and a variable is changed. Volatility is determined when a variable is initialized with a keyword, not a specific data class.

In Objective-C, mutability is limited to specific classes. For example, you must use the NSMutableArray type to be able to resize the array.


What are subscripts?

Subscripts are shortcuts for accessing member elements of a collection, list, or sequence.


What is the difference between Any Object and Generics?

AnyObject does not specify any type, so it will allow you to pass any type, which could lead to a runtime error (which is bad). When you use generics you need to specify the type, so it won't let you pass if you enter the wrong type at compile time (which is good).


What is optional?

Optional is a type that can store a nil value. When it stores a value, it wraps around the value. To enclose a value in an optional parameter, you need to expand it.

Mid iOS Developer Interview Questions


What is the difference between Struct and Class?

Structs are value types and classes are reference types.


Name two types of data structure for memory allocation.

Stack and heap of memory


What is the difference between stack and heap memory?

The stack is a simple first-in-first-out (FIFO) memory structure. The stack is always used to store the following two things: the reference portion of local variables and parameters of the reference type, and local variables and method parameters with a value type.

Heap memory contains random non-lined objects stored in memory. The advantage is that it allows objects to be allocated or released in a random order. This will require you to use garbage collector functions to free memory.

The heap stores the following: the contents of reference type objects.


What are closures?

Standalone functions organized in blocks. They can be transferred and nested within each other. You can pass the closure as an argument to a function, or store it as a property of an object.


What is a type identifier?

It is a pointer to any type in object-c. (Like any in Swift) Since it can store any type, there will be no compilation errors and you can convert it to another type later.


What happens when you call a method on a nil pointer in Objective-C?

This is considered as inaction (no operation). It will simply execute the next instruction. This is not a bug and it will just return nil or 0.


What is the difference between NSArray and NSMutable?

NSArray is used when you don't want to resize or change the data stored in the array. In the NSMutable array, you can add, remove, or change the values ​​in the array.


What is the resolution of the dynamic method?

Compile-time dynamic typing.


In what two ways can you transfer data from one ViewController to another?

By the transition and delegation pattern.


What are input and output parameters? How do you use &(ampersand) in this parameter?

If you use the optional "inout" keyword in a parameter, the original value passed in the parameter will be changed after the function is executed.

func swapTwoInts(_ a: inout Int, _ b: inout Int) {   let temporaryA = a
  a = b
  b = temporaryA

Senior iOS Developer Interview Questions


What is GCD? How is it used?

This is a framework provided by Apple that deals with multiple threads. It is used when you want to work on an asynchronous job. For example, if you want to fetch data from an API, you can use GCD to perform fetch tasks asynchronously.


What is the difference between synchronous and asynchronous jobs?

With synchronous execution, one task does not start until another completes. When scheduling tasks asynchronously, tasks run concurrently.

weak var name: String?


What is Auto Layout?

It is a system in xCode that dynamically calculates the size and position of all views based on the constraints placed on those views.


What is Core Data? What's the use?

The proprietary data storage provided by Apple provides persistent storage. It's easy to manage because you can use xcode to change the model name or attributes. It is native so it is very easy to update it.


Difference between bounds and frame.

UIView borders are location (x, y) and width (x, y), but UIView border refers to the supervisor that UIView contains.


What is a singleton?

A design pattern in programming where you can only use one instance per class. This instance is called a "shared instance".


What is a design pattern?

These are solutions to programming problems like an OOP pattern implemented in the right situation.


What are the three main types of design patterns?

  • behavioral
  • creational
  • structural


What is a delegate pattern?

“A delegate is an object that acts on behalf of or in coordination with another object when that object encounters an event in the program.” © Apple


What is a category in Swift?

Categories is an Objective-c term for fast expansion. Basically, you can extend the closure outside of the class. In objective-c you need to name the extension / category.

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