Animations bound to array values causing EXC_BAD_ACCESS - swiftui

Question

I have a swiftUI view that has a number of animations which are bound to an array of structs. When I test the app on my phone I keep getting EXC_BAD_ACCESS. This is what the top of the backtrace looks like:
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=2, address=0x16f7cfff0)
frame #0: 0x00000001892665c8 SwiftUI`SwiftUI.DefaultCombiningAnimator.value(in: τ_0_0.Value, for: Swift.Double) -> Swift.Optional<τ_0_0.Value> + 48
frame #1: 0x00000001892fac40 SwiftUI`SwiftUI.AnimatorBox.value(in: τ_0_0.Value, for: Swift.Double) -> Swift.Optional<τ_0_0.Value> + 168
frame #2: 0x0000000189264a28 SwiftUI`SwiftUI.AnyAnimator.value(in: τ_0_0, for: Swift.Double) -> Swift.Optional<τ_0_0> + 156
frame #3: 0x0000000189266898 SwiftUI`SwiftUI.DefaultCombiningAnimator.value(in: τ_0_0.Value, for: Swift.Double) -> Swift.Optional<τ_0_0.Value> + 768
frame #4: 0x00000001892fac40 SwiftUI`SwiftUI.AnimatorBox.value(in: τ_0_0.Value, for: Swift.Double) -> Swift.Optional<τ_0_0.Value> + 168
frame #5: 0x0000000189264a28 SwiftUI`SwiftUI.AnyAnimator.value(in: τ_0_0, for: Swift.Double) -> Swift.Optional<τ_0_0> + 156
frame #6: 0x0000000189266898 SwiftUI`SwiftUI.DefaultCombiningAnimator.value(in: τ_0_0.Value, for: Swift.Double) -> Swift.Optional<τ_0_0.Value> + 768
frame #7: 0x00000001892fac40 SwiftUI`SwiftUI.AnimatorBox.value(in: τ_0_0.Value, for: Swift.Double) -> Swift.Optional<τ_0_0.Value> + 168
frame #8: 0x0000000189264a28 SwiftUI`SwiftUI.AnyAnimator.value(in: τ_0_0, for: Swift.Double) -> Swift.Optional<τ_0_0> + 156
The previous 4000 frames all repeat the same sequence of AnyAnimator / AnimatorBox / DefaultCombiningAnimator. The only difference I can see is that in frame #0 the DefaultCombiningAnimator ends in '-> Swift.Optional<τ_0_0.Value> + 48' instead of '+ 768'.
Can anyone give me a clue as to what (if anything) this is telling me. The underlying array is constantly updated but remains a fixed size with no appends or deletions.
This is the animated view element:
ZStack {
//MARK: - Fret Cents Label
NoteLabel()
.fill(activeFret == thisFret ? .white : intonationModel.gString[thisFret].hasBeenSet ? .black : .gray)
.opacity(0.8)
.shadow(color: .black, radius: 4, x: 0, y: 3)
VStack(spacing: 0) {
Text(String(format: "%.1f", cents))
.font(Font.custom("Karantina-Regular", size: scaleHeight * 0.06))
.foregroundColor(activeFret == thisFret ? .black : .white)
}
}
.frame(width: width * 0.9 , height: scaleHeight * 0.1)
.position(x: width * 0.6, y: scaleHeight * 0.5)
.offset(y: yScaleCents * abs(cents) <= 10 ?
scaleHeight * (yScaleCents * 0.05 * -cents) :
scaleHeight * 0.5 * -(abs(cents) / cents))
.animation(.easeInOut(duration: 0.2), value: cents)
This is where it is called in the parent view:
ForEach($intonationModel.gString.indices, id: \.self) { index in
let columnWidth = fretWidth + (120 / (CGFloat(index + 1) * 4))
if index > 0 {
VStack(spacing: 0) {
IntonatorChartColumn(
thisFret: index,
scaleHeight: scaleHeight,
scaleMargin: scaleMargin,
fretboardHeight: fretboardHeight,
fretLabelHeight: fretLabelHeight,
yScaleCents: self.yScaleCents,
stringGap: stringGap,
showFretboard: $showFretboard,
cents: $intonationModel.gString[index].cents,
note: $intonationModel.gString[index].closestNote,
octave: $intonationModel.gString[index].octave,
activeFret: $intonationModel.currentFret
)
.frame(width: columnWidth)
.id(index)
}
.padding(.top, topMargin)
}
}
The app is refusing to crash when I'm looking for zombies, even though it will reliably crash when not being monitored. I'll have a go at re-working my code to avoid the use of indices (as advised by jnpdx).

Answer 1

I believe there were two things going on here.
It seems like the view with the animations was updating even when it was in the background. Ensuring the published variables only updated when the view was in the foreground stopped the crashing.
The incorrect use of ForEach which I've changed to the following:
ForEach(Array(zip(intonationEngine.gString.indices, intonationEngine.gString)) , id: \.0) {index, note in
Since doing this the crashes have stopped.