// 18 Essential iOS Interview Questions

The growing number of iOS users makes the future of iOS app developers quite promising. Innovative devices like the Apple Watch and Apple TV result from iOS and Apple's devoted customer base. There has never been a better time to start a career as an iOS developer. Look no further if you want to start developing for mobile devices. We have compiled a list of top interview questions for your next iOS job interview.

Sometimes even experienced candidates mess up the basics, so do not ignore them. You will also find some common questions for any mobile development interview. So, let us get started!

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Intermediate Level

Briefly explain the Architecture of iOS.

What does it mean to have “deep linking” in iOS?

Write different ways to achieve concurrency in iOS.

What is the use of the SpriteKit and SceneKit frameworks in game development?

Explain what you think are the differences between the assign and retain keywords.

Can you discuss some unique features of Swift that make iOS development efficient?

State the difference between KVC and KVO in Swift.

Briefly explain Test-Driven Development (TDD) in iOS applications.

Identify the issue with the following code. How would you fix it?

@interface TTWaitController : UIViewController

@property (strong, nonatomic) UILabel *alert;

@end

@implementation TTWaitController

- (void)viewDidLoad
{
    CGRect frame = CGRectMake(20, 200, 200, 20);
    self.alert = [[UILabel alloc] initWithFrame:frame];
    self.alert.text = @"Please wait 10 seconds...";
    self.alert.textColor = [UIColor whiteColor];
    [self.view addSubview:self.alert];

    NSOperationQueue *waitQueue = [[NSOperationQueue alloc] init];
    [waitQueue addOperationWithBlock:^{
        [NSThread sleepUntilDate:[NSDate dateWithTimeIntervalSinceNow:10]];
        self.alert.text = @"Thanks!";
    }];
}

@end

@implementation TTAppDelegate

- (BOOL)application:(UIApplication *)application
  didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.rootViewController = [[TTWaitController alloc] init];
    [self.window makeKeyAndVisible];
    return YES;
}

What does it mean to have “dynamic dispatch” in an iOS program?

How can you implement storage and persistence in iOS?

What is the bug in the following code, and how would you fix it?

#import "TTAppDelegate.h"

@interface TTParent : NSObject

@property (atomic) NSMutableArray *children;

@end

@implementation TTParent
@end

@interface TTChild : NSObject

@property (atomic) TTParent *parent;

@end

@implementation TTChild
@end

@implementation TTAppDelegate

- (BOOL)application:(UIApplication *)application
  didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    TTParent *parent = [[TTParent alloc] init];
    parent.children = [[NSMutableArray alloc] init];
    for (int i = 0; i < 10; i++) {
        TTChild *child = [[TTChild alloc] init];
        child.parent = parent;
        [parent.children addObject:child];
    }
    return YES;
}
@end

Beginner Level

Can you explain the difference between atomic and nonatomic properties?

Discuss the various types of iOS Application States.

Using the code below, explain generics in Swift.

func Swapping(x: inout Int, y: inout Int)  
{    
    let temp = x 
    x = y 
    y = temp 
} 
var num1 = 10 
var num2 = 50 
print("Before Swapping: \(num1) and \(num2)") 
Swapping(x: &num1, y: &num2) 
print("After Swapping: \(num1) and \(num2)")

What is the output of the code below?

NSString *firstUserName = @"nick";
NSString *secondUserName = @"nick";

if (firstUserName  == secondUserName)
{
  NSLog(@"areEqual");
}
else
{
  NSLog(@"areNotEqual");
}

What are the major differences between synchronous and asynchronous tasks in iOS?

Using the code, explain the function of the completion handler in iOS.

class CompletionHandler {
    func count() {
        for i in 0...50 {
            if i == 25 {
                if let url = URL(string: "https://scaler.com") {
                    URLSession.shared.dataTask(with: url) { (data, response, error) in
                        print("Received response")
                    }.resume()
                }
            }     
            print("I = ", i)
        }
    }
}
let newInstance = CompletionHandler()
newInstance.count()