Swift: How do I update property when state property changes?

Question

I have a collection of audio files.

I am displaying a collection of cover images for each episode using ACarousel that takes an index $currIndex.

I have a player object. It stores the current episode (player.currentEpisode = episode).

I can reference a particular episode from outside the carousel loop like so: player.episodes[currIndex].

I want to change player.currentEpisode every time currIndex updates: player.currentEpisode = player.episodes[currIndex]. I thought I could do this using didSet or willSet but it appears these aren't fired.

Why don't didSet or willSet fire? How can I update player.currentEpisode when currIndex updates?

struct ContentView: View { @EnvironmentObject var player: Player ... @State var currIndex: Int = 0 { didSet { print("Did set currIndex") // Nothing output to console } willSet { print("Will set currIndex") // Nothing output to console } } var body: some View { VStack { ACarousel(player.episodes, id: \.id, index: $currIndex, spacing: width/5, sidesScaling: 0.7, isWrap: true) { episode in VStack { Image(episode.image) } } ...

Asperi · Accepted Answer · 2022-06-30 13:30:37Z

Use instead onChange(of: ), like

@State var currIndex: Int = 0 var body: some View { VStack { ACarousel(player.episodes, id: \.id, index: $currIndex, spacing: width/5, sidesScaling: 0.7, isWrap: true) { episode in VStack { Image(episode.image) } } .onChange(of: currIndex) { [currIndex] newValue in // << here !! print("Old value: \(currIndex)") print("New value: \(newValue)") }

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