SwiftUI: How to use withAnimation in a ScrollView? - ios

Question

I've been trying to animate a ScrollView using ScrollViewReader and withAnimation.
I can't figure out why these two animations are not working, either from Button or .onAppear?
import SwiftUI
struct ScrollView2: View {
#State private var scrollText = false
var body: some View {
ScrollViewReader { scrollView in
ScrollView {
Button("Scroll to bottom") {
withAnimation(.linear(duration: 30)) {
scrollView.scrollTo(99, anchor: .center)
}
}
ForEach(0..<100) { index in
Text(String(index))
.id(index)
}
.onAppear(perform: {
withAnimation(.linear(duration: 30)) {
scrollView.scrollTo(scrollText ? 99 : 1, anchor: .center)
}
scrollText.toggle()
})
}
}
}
}

Answer 1

It seems like duration doesn't work within withAnimation. Alternatively, I created a function that executes a repeating Timer that fires over 30 seconds, calling scrollTo withAnimation on each loop.
struct ScrollView2: View {
#State private var scrollText = false
var body: some View {
ScrollViewReader { scrollView in
ScrollView {
Button("Scroll to bottom") {
animateWithTimer(proxy: scrollView)
}
ForEach(0..<100) { index in
Text(String(index))
.id(index)
}
}
}
}
func animateWithTimer(proxy: ScrollViewProxy) {
let count: Int = 100
let duration: Double = 30.0
let timeInterval: Double = (duration / Double(count))
var counter = 0
let timer = Timer.scheduledTimer(withTimeInterval: timeInterval, repeats: true) { (timer) in
withAnimation(.linear) {
proxy.scrollTo(counter, anchor: .center)
}
counter += 1
if counter >= count {
timer.invalidate()
}
}
timer.fire()
}
}
Note: There is a delay when you press the button initially because when it tries to scrollTo the first ~40 of numbers, they are already high on the screen and the scrollView doesn't need to scroll anywhere to center them. You can update the timeInterval and counter variables as needed.

Answer 2

Because duration doesn't seem to work with withAnimation yet, I had to be a bit hacky to get the animation effect I wanted.
Here's what I did:
I added a ScrollViewReader to my ScrollView
I used ForEach and added IDs to my items in my ScrollView
Used an .offset and .animation modifiers to animate the
ScrollView itself (not the items in it)
Used .scrollTo within .onAppear to move at launch the ScrollView
to an item further away from the start to allow the user to both
scroll back and forward the items, even with the ScrollView being
itself animated from right to left
Here's what my code looks like:
import SwiftUI
import AVKit
struct ProView: View {
#State private var scrollText = false
var body: some View {
ZStack {
// VStack {
// Color(#colorLiteral(red: 0, green: 0, blue: 0, alpha: 1))
// .ignoresSafeArea(.all)
// }
//
// VStack {
//
// VideoPlayer(player: AVPlayer(url: Bundle.main.url(forResource: "wave-1", withExtension: "mp4")!)) {
// VStack {
// Image("pro-text")
// .resizable()
// .frame(width: 200, height: .infinity)
// .scaledToFit()
// }
// }
// .ignoresSafeArea(.all)
// .frame(width: .infinity, height: 300)
ScrollView(.horizontal, showsIndicators: false) {
ScrollViewReader { value in
HStack(spacing: 5) {
ForEach(0 ..< 100) { i in
HStack {
Image("benefit-1")
.resizable()
.frame(width: 120, height: 120)
Image("benefit-2")
.resizable()
.frame(width: 120, height: 120)
Image("benefit-3")
.resizable()
.frame(width: 120, height: 120)
Image("benefit-4")
.resizable()
.frame(width: 120, height: 120)
Image("benefit-5")
.resizable()
.frame(width: 120, height: 120)
Image("benefit-6")
.resizable()
.frame(width: 120, height: 120)
Image("benefit-7")
.resizable()
.frame(width: 120, height: 120)
Image("benefit-8")
.resizable()
.frame(width: 120, height: 120)
Image("benefit-9")
.resizable()
.frame(width: 120, height: 120)
Image("benefit-10")
.resizable()
.frame(width: 120, height: 120)
}
.id(i)
}
}
.offset(x: scrollText ? -10000 : 20)
.animation(Animation.linear(duration: 300).repeatForever(autoreverses: false))
.onAppear() {
value.scrollTo(50, anchor: .trailing)
scrollText.toggle()
}
}
}
Spacer()
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ProView()
}
}