Swift

Question 1

Differences Between Classes and Structs

Answer 1

Structs are are accessed as “by value” (using as a param creates a copy) and classes are accessed “by reference” (using as a param passes a pointer).

Classes can inherit from other classes, structs can’t

Question 2

Which is Better - Class or Struct

Answer 2

Class better for inheritance

Struct better for passing between threads, optimize performance
(FASTER since they are allocated on STACK and classes are allocated on HEAP)

Question 3

Advantages of Array

Answer 3

Easy access by index

More type-safe (can only contain 1 type of element)

Arrays have many built-in operations (add, remove, filter, sort, etc)

Question 4

What property is used to allow objects to be serialized/deserialized ?

Answer 4

struct Person: Codable { .. }

All properties need to support codable to be serialized

Then use JsonDecoder()

Question 5

How to handle custom property names when encoding / decoding to JSON

Answer 5

Use CodingKeys enum

enum CodingKeys: String, CodingKey {
case name = “full_name”
case age
case address
}

Question 6

What are the 5 different access levels in Swift

Answer 6

open - can be accessed / subclassed

public - accessible but not subclass-able

internal - accessible from same MODULE - DEFAULT LEVEL

fileprivate - accessible from same FILE

private - accessible from same class / struct

Question 7

What are extensions and why use them

Answer 7

Allow adding new functionality to class / struct (even if source not available)

Group related functionality

Add protocol conformance to a class /struct

Question 8

Can you add new properties to class/struct using extensions

Answer 8

Stored properties cannot be added

Computed properties can be added

Reason - A TYPES MEMORY LAYOUT IS DETERMINED AT COMPILE TIME

Question 9

What are associated types ?

Answer 9

Generics for protocols

Question 10

Why use a protocol ?

Answer 10

interface reusability with different types

Abstraction

Dependency injection - more flexible and testable

Question 11

Auto Layout

Answer 11

content hugging - when high, view wants to become as SMALL AS POSSIBLE on that axis

compression resistance - when HIGH, the view wants to become AS BIG AS POSSIBLE on that axis

Question 12

What are size classes

Answer 12

Currently only 2

compact and regular
A device has a size class for each dimension

In Storyboard, you can create ANY, ANY for the default layout and then specific layouts for a particular combination of size classes

Question 13

UIViewController events (in order)

Answer 13

loadView() - Called before the view is created
viewDidLoad()
viewWillLayoutSubviews()
viewDidLayoutSubviews()
viewWillAppear()
viewDidAppear()

viewWillDisappear()
viewDidDisappear()

Question 14

Ways to Pass Data Between UIViewControllers

Answer 14

A delegate method - 1 to 1
Post a notification - 1 to many
Dependency injection (params passed when invoked)
Use a closure on the invoked VC

Question 15

What are different ways to adjust UITableview cell sizes at runtime

Answer 15

tableView: heightForRowAtIndex:

Use self-sizing cells (must have a continuous sequence of constrains from top to bottom). rowHeight = automaticDimension

Question 16

Tell me about UIViewController navigationItem

Answer 16

Contains nav bar title

Contains rightBarButtonItem / leftBarButtonItem

Question 17

Ways to present a UIViewController

Answer 17

Fullscreen

PageSheet- partial screen (bottom). VC can be pulled down with a swipe

overCurrentContext - Hides the current VC context

Question 18

How to create custom transitions between VCs

Answer 18

Implement the UIViewControllerAnimatedTransitioning protocol

Question 19

How to share small data between app and app extension ?

Answer 19

UserDefaults

Setup AppGroup
Enable to app and extension in Portal
UpdateXcode project (the same)
Use appGroup identifier (suiteName:) when accessing UserDefaults

Question 20

How to store objects in UserDefaults ?

Answer 20

NSKeyedArchiver - converts object to Data type (more efficient on large objects)

JsonEncoder - also converts to Data object

Question 21

File System - What is the use case for Documents folder ?

Answer 21

Items created / edited by the user. backed up to iCloud

Question 22

File System - What is the use case for Library folder ?

Answer 22

App-specific data not created by the user - downloaded content, preferences. Backed up to iCloud

Question 23

File System - What is the use case for Cache folder ?

Answer 23

Storage for temporary files - not backed up to iCloud. Can be purged when device runs low on disk space

Question 24

File System - What is the use case for Temp folder

Answer 24

Temp files. Deleted when app is closed

Question 25

CocoaPods - difference between “pod install” and “pod update”

Answer 25

“pod install” installs the dependencies in the POD file

“pod update” updates the dependencies to the latest minor version

Question 25

How to implement Push Notifications in an app

Answer 25

• Add Push Notif capability
• Generate either:
  
  • Push SSL cert - good for 1 year, limited to single app
  • APNS token - good until revoked, can send to all apps
• Regenerate and DL new provisioning profile
• In application:didFinishLaunching, add call to requestAuthorization (for call user will see system dialog to allow / disallow PN)
• if granted, on main thread call UIApplication.shared.registerForRemoteNotifications()
• Handle callback to UIApplication didRegisterForRemoteNotifications (device token)
• Handle PN while app is open - userNotificationCenter:willPresent:WithCompletionHandler
• Handle clicking on PN - application:didReceiveRemoteNotification:userInfo:

Question 26

How is class inheritance and protocol extension different ?

Answer 26

Class inheritance is vertical (you get everything defined above in the hierarchy)

Protocol extensions are more horizontal. You can pick and choose which protocol you want to adapt (and leave others out). They can also work on structs and enums.

Question 27

Best Way to Approach Concurrency

Answer 27

1 - simple await call
2 - async let (for multiple concurrent tasks)
async let x = …
async let y = …
let z = await[x,y]
3 - BlockOperation / OperationQueue
4 - Task (allows cancelling work or passing results around)
5 - Task Group

Question 28

How do dispatch queues handle concurrency ?

Answer 28

When creating the dispatch queue, the attribute parameter determines if it is serial (default) or concurrent

Question 29

How to run code on the main thread ?

Answer 29

DispatchQueue.main.async(execute:)

Question 30

How do dispatch queues handle blocking ?

Answer 30

Method call used

dispatchQ.async { }
dispatchQ.sync {}

Question 31

How to enqueue work on an OperationQueue ?

Answer 31

let blockOp1 = BlockOperation.init(block: { … })
let blockOp2 = BlockOperation.init(block: {…})
let operationQ = OperationQueue()
opQ.addOperation(blockOp1)
opQ.addOperation(blockOp2)

Also .addOperation can be used to add operations directly without using Blocks

Question 32

How do OperationQueues handle concurrency ?

Answer 32

OperationQueue is concurrent by default FOR OPERATION BLOCKS not execution blocks

To get a serial OperationQueue, set operationQ.maxConcurrentOperationCount

Question 33

What is a good use for serial dispatch queues ?

Answer 33

Serial queues are often used to synchronize access to a specific resource, since it is guaranteed that only 1 task will execute at a time.