SwiftUI View method called but output missing - swift

Question

I have the View AlphabetLetterDetail:
import SwiftUI
struct AlphabetLetterDetail: View {
var alphabetLetter: AlphabetLetter
var letterAnimView : LetterAnimationView
var body: some View {
VStack {
Button(action:
animateLetter
) {
Image(uiImage: UIImage(named: "alpha_be_1")!)
.resizable()
.scaledToFit()
.frame(width: 60.0, height: 120.0)
}
letterAnimView
}.navigationBarTitle(Text(verbatim: alphabetLetter.name), displayMode: .inline)
}
func animateLetter(){
print("tapped")
letterAnimView.timerWrite()
}
}
containing the View letterAnimView of Type LetterAnimationView:
import SwiftUI
struct LetterAnimationView: View {
#State var Robot : String = ""
let LETTER =
["alpha_be_1_81",
"alpha_be_1_82",
"alpha_be_1_83",
"alpha_be_1_84",
"alpha_be_1_85",
"alpha_be_1_86",
"alpha_be_1_87",
"alpha_be_1_88",
"alpha_be_1_89",
"alpha_be_1_90",
"alpha_be_1"]
var body: some View {
VStack(alignment:.center){
Image(Robot)
.resizable()
.frame(width: 80, height: 160, alignment: .center)
.onAppear(perform: timerWrite)
}
}
func timerWrite(){
var index = 0
let _ = Timer.scheduledTimer(withTimeInterval: 0.08, repeats: true) {(Timer) in
Robot = LETTER[index]
print("one frame")
index += 1
if (index > LETTER.count - 1){
Timer.invalidate()
}
}
}
}
This gives me a fine animation, as coded in func timerWrite() and performed by .onAppear(perform: timerWrite).
After commenting //.onAppear(perform: timerWrite) I try animating by clicking
Button(action: animateLetter)
but nothing happens.
Maybe I got two different instances of letterAnimView, if so why?
Can anybody of you competent guys intentify my mistake?
Regards - Klaus

Answer 1

You don't want to store Views, they are structs so they are copied. Instead, create an ObservableObject to encapsulate this functionality.
I created RobotModel here with other minor changes:
class RobotModel: ObservableObject {
private static let atlas = [
"alpha_be_1_81",
"alpha_be_1_82",
"alpha_be_1_83",
"alpha_be_1_84",
"alpha_be_1_85",
"alpha_be_1_86",
"alpha_be_1_87",
"alpha_be_1_88",
"alpha_be_1_89",
"alpha_be_1_90",
"alpha_be_1"
]
#Published private(set) var imageName: String
init() {
imageName = Self.atlas.last!
}
func timerWrite() {
var index = 0
let _ = Timer.scheduledTimer(withTimeInterval: 0.08, repeats: true) { [weak self] timer in
guard let self = self else { return }
self.imageName = Self.atlas[index]
print("one frame")
index += 1
if index > Self.atlas.count - 1 {
timer.invalidate()
}
}
}
}
struct AlphabetLetterDetail: View {
#StateObject private var robot = RobotModel()
let alphabetLetter: AlphabetLetter
var body: some View {
VStack {
Button(action: animateLetter) {
Image(uiImage: UIImage(named: "alpha_be_1")!)
.resizable()
.scaledToFit()
.frame(width: 60.0, height: 120.0)
}
LetterAnimationView(robot: robot)
}.navigationBarTitle(Text(verbatim: alphabetLetter.name), displayMode: .inline)
}
func animateLetter() {
print("tapped")
robot.timerWrite()
}
}
struct LetterAnimationView: View {
#ObservedObject var robot: RobotModel
var body: some View {
VStack(alignment:.center){
Image(robot.imageName)
.resizable()
.frame(width: 80, height: 160, alignment: .center)
.onAppear(perform: robot.timerWrite)
}
}
}