Swift

• Backticks around identifiers are ignored, and allow you to use reserved words as identifiers (ex. `default`)
• Closure arguments can be accessed using $0, $1, etc.
• \typename.path represents a key path to a property
  • typename can be omitted if it can be inferred
  • path can include multiple periods, subscripts (if parameter conforms to Hashable), can use optional chaining or force unwrapping
  • can use a key path expression whose root type is SomeType and whose path produces a value of type Value, instead of a function or closure of type (SomeType) -> Value
• separate multiple conditions in if statements using , (instead of &&)
• Create a dictionary which groups items by the results of a closure:

let students = ["Kofi", "Abena", "Efua", "Kweku", "Akosua"]
let studentsByLetter = Dictionary(grouping: students, by: { $0.first! })
// ["E": ["Efua"], "K": ["Kofi", "Kweku"], "A": ["Abena", "Akosua"]]

SwiftUI

Model/State

• Create a model object that inherits from ObservableObject to hold reactive state that views can share
  • import Combine
  • An observable object needs to publish any changes to its data using the @Published attribute, so that its subscribers can pick up the change
    • if a property will never change, no need to add @Published
  • Use the @StateObject attribute when initializing the model object (ex. in the App instance) to ensure it is initialized only once during the life time of the app
    • @StateObject private var modelData = ModelData()
  • use the .environmentObject modifier to pass the state object down to child views (in the App instance or in previews)
    • .environmentObject(ModelData())
  • use the @EnvironmentObject attribute in child views to receive the state object
    • @EnvironmentObject var modelData: ModelData
• Use state properties (marked with @State) to hold information that’s specific to a view and its subviews
  • always create state as private
• By prefixing a state (or state object) variable with $, you pass a binding which can be updated by the view it's passed into
• Use @Binding on a view property to propagate changes upwards

/* LandmarkDetail.swift */
@EnvironmentObject var modelData: ModelData
...
FavoriteButton(isSet: $modelData.landmarks[landmarkIndex].isFavorite)

/* FavoriteButton.swift */
@Binding var isSet: Bool

Views

• To change alignment in Text view:

Text("Hello world")
    .frame(width: 100, alignment: .leading)

• Group can be used to apply modifiers to a bunch of child views
• ForEach renders a bunch of views individually without creating a new container
  • To use ForEach on an array and get the index:

ForEach(Array(zip(items.indices, items)), id: \.1) { index, item in
    ...
}

• When iterating using List, ForEach, etc, must provide a keypath for a unique id unless the objects being iterated over implement Identifiable

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