iOS Basic Interview

interview.md

#iOS Interview

1. Snippets

• Какие есть проблемы с этим кодом?

// OTTAvatarView.h

#import <UIKit/UIKit.h>

@interface OTTAvatarView : UIView

- (nonnull instancetype) initWithImage: (nonnull UIImage *) image
                           onTapAction: (void(^ _Nullable)()) action NS_DESIGNATED_INITIALIZER;

@property (nullable) void(^action)();

@end

// OTTAvatarView.m

@interface OTTAvatarView ()
@property UIImageView *imageView;
@end

@implementation OTTAvatarView

- (instancetype) initWithImage: (UIImage *) image
                   onTapAction: (void(^)()) action
{
  if (self = [super initWithFrame: CGRectZero])
  {
    self.action = action;
    
    UIImageView *imageView = [UIImageView new];
    [self addSubview: imageView];
    
    self.imageView = imageView;
    
    self.imageView.image = image;
    
    UITapGestureRecognizer *tapRec = [UITapGestureRecognizer new];
    [tapRec addTarget: self action: @selector(onTap:)];
    [self.imageView addGestureRecognizer: tapRec];
  }
  return self;
}

- (void) onTap: (UITapGestureRecognizer *) tapRec
{
  self.action();
}

@end

• Что выведется в консоль в при выполнении метода -method объекта класса C?

@interface A : NSObject
- (void)someMethod;
@end

@implementation A
- (void)someMethod {
    NSLog(@"This is class A");
}
@end

@interface B : A
@end

@implementation B
- (void)someMethod {
    NSLog(@"This is class B");
}
@end

@interface C : NSObject
@end

@implementation C
- (void)method {
    A *a = [B new];
    [a someMethod];
}

• Выведется ли в консоль «Hello world»? Почему?

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    dispatch_sync(dispatch_get_main_queue(), ^{
        NSLog(@"Hello world");
    });

   /* Another implementation */
   return YES;
}

• Какие есть проблемы с этим кодом?

@interface OTTPlayground : NSObject
@end

@implementation OTTPlayground

- (void) post
{
  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    [[NSNotificationCenter defaultCenter] postNotificationName: @"someNotification" object: nil];
  });
}

- (void) subscribe
{
  dispatch_async(dispatch_get_main_queue(), ^{
    [[NSNotificationCenter defaultCenter] addObserver: self
                                             selector: @selector(someMethod)
                                                 name: @"someNotification"
                                               object: nil];
  });
}

- (void) someMethod
{
  NSLog(@"Hello world");
}

- (instancetype) init
{
  if (self = [super init])
  {
    [self subscribe];
    [self post];
  }
  return self;
}

@end

• Что выведется в консоль?

__block int i = 0; 
dispatch_async(dispatch_get_main_queue(), ^{
    NSLog(@"A %d", ++i);
    dispatch_async(dispatch_get_main_queue(), ^{
        NSLog(@"B %d", ++i);
    });
    NSLog(@"C %d", ++i);
});
NSLog(@"D %d", ++i);

• Что будет выведено в консоль?

- (void) method
{
    int i = 0;
    void (^block)() = ^{
        ++i;
    };
    
    block();
    NSLog(@"%d", i);
}

• Все ли в порядке с этим кодом?

- (void)viewDidLoad
{
    UILabel *label = [UILabel new];
    label.text = @"Pending...";
    [self.view addSubview: label];
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        label.text = @"Some text";
    });
}

2. Language Mechanisms

Objective C

• Runtime and Messaging (isa, selector, object structure)
• Categories and extensions (caveats, usecases)
• Blocks (nature, __block, memory caveats)

Swift

• Enums. What's different from C.
• Optionals. Mechanism and usecases.

3. Platform

• Memory Management (Paradigm, MRC, ARC)
• Layout (Auto, Manual. Storyboards, Xibs. Constraint, AutoresizingMask)

4. Architecture

• Patterns (SOLID, SOA, Modul Constuction Concepts (MVC, MVVM, VIPER))

#Interviewer cheatsheet

• Code sharing: CodeShare, Kobra