Swift Flashcards
Differences Between Classes and Structs
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
Which is Better - Class or Struct
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)
Advantages of Array
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)
What property is used to allow objects to be serialized/deserialized ?
struct Person: Codable { .. }
All properties need to support codable to be serialized
Then use JsonDecoder()
How to handle custom property names when encoding / decoding to JSON
Use CodingKeys enum
enum CodingKeys: String, CodingKey {
case name = “full_name”
case age
case address
}
What are the 5 different access levels in Swift
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
What are extensions and why use them
Allow adding new functionality to class / struct (even if source not available)
Group related functionality
Add protocol conformance to a class /struct
Can you add new properties to class/struct using extensions
Stored properties cannot be added
Computed properties can be added
Reason - A TYPES MEMORY LAYOUT IS DETERMINED AT COMPILE TIME
What are associated types ?
Generics for protocols
Why use a protocol ?
interface reusability with different types
Abstraction
Dependency injection - more flexible and testable
Auto Layout
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
What are size classes
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
UIViewController events (in order)
loadView() - Called before the view is created
viewDidLoad()
viewWillLayoutSubviews()
viewDidLayoutSubviews()
viewWillAppear()
viewDidAppear()
viewWillDisappear()
viewDidDisappear()
Ways to Pass Data Between UIViewControllers
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
What are different ways to adjust UITableview cell sizes at runtime
tableView: heightForRowAtIndex:
Use self-sizing cells (must have a continuous sequence of constrains from top to bottom). rowHeight = automaticDimension
Tell me about UIViewController navigationItem
Contains nav bar title
Contains rightBarButtonItem / leftBarButtonItem
Ways to present a UIViewController
Fullscreen
PageSheet- partial screen (bottom). VC can be pulled down with a swipe
overCurrentContext - Hides the current VC context
How to create custom transitions between VCs
Implement the UIViewControllerAnimatedTransitioning protocol
How to share small data between app and app extension ?
UserDefaults
Setup AppGroup
Enable to app and extension in Portal
UpdateXcode project (the same)
Use appGroup identifier (suiteName:) when accessing UserDefaults
How to store objects in UserDefaults ?
NSKeyedArchiver - converts object to Data type (more efficient on large objects)
JsonEncoder - also converts to Data object
File System - What is the use case for Documents folder ?
Items created / edited by the user. backed up to iCloud
File System - What is the use case for Library folder ?
App-specific data not created by the user - downloaded content, preferences. Backed up to iCloud
File System - What is the use case for Cache folder ?
Storage for temporary files - not backed up to iCloud. Can be purged when device runs low on disk space
File System - What is the use case for Temp folder
Temp files. Deleted when app is closed
CocoaPods - difference between “pod install” and “pod update”
“pod install” installs the dependencies in the POD file
“pod update” updates the dependencies to the latest minor version
How to implement Push Notifications in an app
- 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:
How is class inheritance and protocol extension different ?
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.
Best Way to Approach Concurrency
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
How do dispatch queues handle concurrency ?
When creating the dispatch queue, the attribute parameter determines if it is serial (default) or concurrent
How to run code on the main thread ?
DispatchQueue.main.async(execute:)
How do dispatch queues handle blocking ?
Method call used
dispatchQ.async { }
dispatchQ.sync {}
How to enqueue work on an OperationQueue ?
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
How do OperationQueues handle concurrency ?
OperationQueue is concurrent by default FOR OPERATION BLOCKS not execution blocks
To get a serial OperationQueue, set operationQ.maxConcurrentOperationCount
What is a good use for serial dispatch queues ?
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.
