/SwiftNotes

SwiftNotes 📱

Arrays

  • arrayName.append(newElement: Type): adds single element to array
  • arrayName.append(contentsOf: Sequence): adds another array at the end of arrayName
  • arrayName.first(where: { CONDITION }): takes first element in array that satisfies the condition
    • Ex: let firstNegative = arrayOfNumbers.first(where: { $0 < 0 })

Closures

  • Basically anonymous functions
  • Code before in is like a function's parameters, code after is like a function's body
    • Can ignore in and () -> () if there's no parameters (remove everything before in)
  • $0 refers to 1st parameter, $1 refers to 2nd parameter, and so on
  • Swift can infer type
  • Returning closures
    • func returnClosure() -> ((Int, Int) -> Int) { return {$0 + $1} }
    • Call: let varName = returnClosure(), and then varName(5,5)
  • Trailing closure
    • If closure is last parameter in a func being called, can close off func like this: funcName(int: 100) { $0 * 2 }

Functions

Lazy

  • Only uses value set for var when it's needed

Programmatic UI

  • Auto Layout (cheat sheet)
    • Anchors: efficient to pass them as array to activate/deactivate (NSLayoutConstraint.activate([...]) or NSLayoutConstraint.deactivate([...])
      • Ex: leadingAnchor, trailingAnchor, topAnchor, bottomAnchor
    • For trailingAnchor and bottomAnchor, constant needs to be -ve
      • Ex: viewName.bottomAnchor.constraint(equalTo: parentView.bottomAnchor, constant: -10)
  • Content Hugging Priorities and Compression Resistance Priorities

SwiftUI

  • Drag and drop, live preview, cross platform (iOS/macOS/watchOS)
  • VHZ Stacks
  • Easy to extract views and reuse code (like instantiating objects)

Optionals (?) • Force Unwrapping (!) • Optional Binding (if let) • Nil Coalescing Operator (??)

  • Optional: variable that holds either a value or no value (nil)
    • Ex: let myOptional: String?, myOptional can either be a string value or nil
  • Force unwrapping: use ! when confident that the variable will never be nil
    • Ex: let text: String = myOptional!, used because myOptional will never be nil
  • Optional Binding: checks to see variable is nil, then procedes if it's not
    • Ex: if let safeOptional = myOptional {...}, myOptional is the variable you want to check, and safeOptional is the temporary variable you use inside the if-block if it is indeed not nil
  • Nil Coalescing Operator: defaults to value after ?? if variable before it is nil
    • Ex: let text: String = myOptional ?? "Default Value", text will be myOptional if it's not nil, otherwise if myOptional is nil then text will be "Default Value"

Guard let vs If let

  • guard let focuses on ideal path where variable is non-nil
    • Common at start of methods to verify conditions are correct upfront
    • Use if let if you just want to unwrap some optionals, use guard let if you’re specifically checking that conditions are correct before continuing
    • Variable in if let isn't in scope of subsequent else statement, need guard let for that (used after else in guard let)

as • as? • as!

Tuple

  • Data structure that holds a group of values (can be different types)
  • Ex: let product = (name: "MacBook", price: 1099.99), to get "MacBook" you do product.0/product.name and to get 1099.99 you do product.1/product.price

Map • FlatMap • CompactMap

  • Map: method that can transform a sequence of elements
    • Ex: let strings = ["one", "two", "three"], let ints = strings.map { $0.count } would return [3,3,5]
    • Can also use mapValues() for dictionaries to transform dictionary values (returns a dictionary)

Protocols

  • ListDiffable provides methods needed to compare the identity and equality of 2 objects (need to import IGListKit)

UITableView

  • Search for Table View in Objects library
    • Made up of Table View Cells (Prototype Cells)
    • Need identifier
    • UITableViewDataSource protocol
    • UITableViewDelegatefor when user taps on UITableView
  • To improve UI
    • Create new Cocoa Touch class (subclass of UITableViewCell, also create XIB file)
    • Use this for Table View Cells' design

UILabel

Delegates

Model-View-Controller (MVC)

  • Model: stores data, View: displays data, Controller: responds to user + manipulates model
  • User uses controller, controller manipulates model, model sends data to view, view renders itself to user
  • Advantages
    • Well-known, separate responsibilities are clear, data flow is clear
  • Disadvantages
    • Controller ends up being huge, blurred separation of concerns, hard to test, leads to small views/models

Model-View-Presenter (MVP)

  • Model stores data that'll be displayed to user, View stores passive UI elements that forward user interaction, Presenter reads data from model + displays it in views

Model-View-ViewModel (MVVM)

Coordinator

In-App Purchases

  • 30% transaction fee
  • Tip: make app free to download and give user 80% of full functionality of app, then use paywall (in-app purchases) for advanced functionality like removing ads/premium features/etc.
  • Need Apple Developer program and physical device to simulate in-app purchases
  • App Store Connect
    • Sandbox testers
  • Capabilities --> In-App Purchase --> ON
  • import StoreKit
    • SKPaymentQueue.canMakePayments() returns a boolean
    • SKMutablePayment() NSObject
    • SKPaymentTransactionObserver protocol
    • SKPaymentTransactionState --> purchasing, purchased, failed, restored, deferred
    • UserDefaults are wiped clean if user gets new phone/updates iOS/etc., so a restore button is needed to check if a user has already purchased

CoreML

  • Allows you to load a pre-trained model and make predictions (no training, static, not encrypted)
  • ML: Teaching a machine how to do something by training it over and over again
    • Model is fed training data
  • Supervised (loads of images with labels, like regression/classification) vs unsupervised (unlabelled, like clustering)
  • Reinforcement learning: +ve and -ve rewards, like maximizing chess win chances by examining win probability after each move

ARKit

  • SceneKit (3D), SpriteKit (2D), Metal
  • art.scnassets folder has cool spaceship

Design Tools

Open Source Libraries

Developer Tools

To Do

  • Filter
  • Reduce