SwiftUI animation within ScrollView not working

Question

Just can't get my head around this. I have a simple animation which works perfectly. But when I wrap the view into a ScrollView (by uncommenting the 2 lines) it does not animate anymore? Anybody a clue?

import SwiftUI

struct ContentView: View {
    @State var offset = CGSize(width: 0, height: 0)

    var body: some View {
//      ScrollView {
            VStack(spacing: 50) {
                Rectangle()
                    .frame(width: 100, height: 100)
                    .offset(self.offset)
                Button(action: {
                    withAnimation {
                        self.offset.width += 66
                    }
                })
                {
                    Text("Animate me")
                }
            }.frame(width: 300)
//      }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

I tried your code and it works fine in the simulator. The rectangle animates when it is contained in the ScrollView. The only difference that I noticed was that the button and rectangle were at the top of the screen rather than in the centre. — Andrew
– Andrew, Commented Oct 26, 2019 at 14:04
@Andrew copy pasting the code in the question I have the same problem of iTukker: animation won't work if it's inside the ScrollView. Which xCode version are you using? — superpuccio
– superpuccio, Commented Oct 26, 2019 at 14:06
@superpuccio Xcode 11.1, tried it both in the simulator and the preview and it works. — Andrew
– Andrew, Commented Oct 26, 2019 at 14:07
@Andrew I'm using that version too. Very strange. I have the same problem of iTukker. — superpuccio
– superpuccio, Commented Oct 26, 2019 at 14:08
I am on Xcode 11.1 as well, and no success. @superpuccio's answer did the trick, I'll accept that one. Still learning SwiftUI and already stumbled on my first animation. — iTukker
– iTukker, Commented Oct 26, 2019 at 14:11

superpuccio · Accepted Answer · 2019-10-26 14:01:48Z

1

I've already noticed this behaviour. The issue seems to be the explicit animation. If you go for an implicit animation it works:

struct ContentView: View {
    @State var offset = CGSize(width: 0, height: 0)

    var body: some View {
      ScrollView {
            VStack(spacing: 50) {
                Rectangle()
                    .frame(width: 100, height: 100)
                    .offset(self.offset)
                    .animation(.linear)
                Button(action: {
                    self.offset.width += 66
                })
                {
                    Text("Animate me")
                }
            }.frame(width: 300)
      }
    }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}

I haven't managed to get the reason yet, so consider this as a workaround. It may be a SwiftUI bug or something I still can't understand.

answered Oct 26, 2019 at 14:01

superpuccio

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1 Comment

iTukker Over a year ago

That did the trick, thanx. Still agree that it seems a bug though.

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