Swift Etudes

Tom's SwiftUI experimentation spot.

Blog

Day 1: Haptic Image

Made a haptic image tap animation + project organisation

Learned about:

• NavigationStack
• HStack, VStack, ZStack
• AppIcon asset
• Image assets
• Feedback Generators (UIImpactFeedbackGenerator)
• modifiers
• safeArea

Day 2: Palette Generator

Made a grid of rectangles colored by a random starting color and each subsequent color has a hue rotation applied.

Learned about:

• systemIcon (SF Symbols) - they have a cool explorer app here: https://developer.apple.com/sf-symbols/
• ForEach view
• @State
• withAnimation - really cool pattern. Creates an animation based on some change to a view. (e.g selectedColor may be set in the closure and and will have effects on other views that conditionally render based on this state. The animation will then effect all those dependent views. I have no idea how this works but it's a really nice dev experience so far.)
• matchedGeometryEffect modifier for animations. You can tie two views together with a unique id to enable SwiftUI to work out how to transition between two states, even if the two views are distinct.

Day 3: HN

Made a simple HN client using their firebase API. The firebase API at https://hacker-news.firebaseio.com/v0. This API has some complexity as /topstories.json will return back a list of ids and you have to fetch each story individually.

Learned about:

• Alamofire library for making HTTP requests
  • has a cool .responseDecodable(of: Story.self) method which can parse the json response into a struct that conforms to the Codable protocol.
• installing dependencies
• @StateObject and @EnvironmentObject
  • Both are for services/classes that extend ObservableObject like our HNService.
  • @StateObject is for when you initialize the class in the view it is being used.
  • @EnvironmentObject is like dependency injection. You initialize the class further up the tree and it is injected into this view
    • (claude-3.5-sonnet used the react analogy of useContext)
• DispatchGroup() for asynchronous tasks
  • create a new group
  • add a task into the group with group.enter() (do your request etc)
  • group.leave() once the task is done
    • The swift way to do this is to use defer, which will execute once you exit the scope of the current codeblock, regardless of errors etc.
  • group.notify() to inform that all of the async tasks have been completed
• guard I don't really understand. It feels like guard (!isLoading) else { return } it is the same as doing if (isLoading) { return } ... and just different syntax for expressing that. It might be slightly more readable? idk.
• lists
  • you can do the "pull to refresh" with .refreshable { } modifier

Day 4: HN Improvements

• Swipe list to open in safari
• Sheet to open a webview with the hn story
• Render the hn score in the list

Day 5: PID Controller

• Inspired by a physiology course I'm taking. Human homeostasis seems like a bunch of PID controllers.

• Attempted to build a PID controller in swift
• Still don't know exactly how you are meant to tune the P,I,D gain values in a PID controller?
• Learned a tiny bit about swift charts:

Chart(temperatureData) { data in
    LineMark(
        x: .value("Time", data.time),
        y: .value("Temperature", data.temperature)
    )
    .foregroundStyle(.blue)
    RuleMark(y: .value("Setpoint", self.setpoint))
        .foregroundStyle(.red)
}
.frame(height: 300)

• Learned about the Timer class ... similar to setInterval:

Timer.scheduledTimer(withTimeInterval: deltaTime, repeats: true) { _ in
    // do it
}