SwiftUI Text animation on opacity does not work

Question

Question is simple: how in the world do i get a Text to animate properly?

struct ContentView: View {
    @State var foozle: String = ""

    var body: some View {
        VStack() {
            Spacer()

            Text(self.foozle)
                .frame(maxWidth: .infinity)
                .transition(.opacity)

            Button(action: {
                withAnimation(.easeInOut(duration: 2)) {
                    self.foozle = "uuuuuuuuu"
                }
            }) { Text("ugh") }

            Spacer()
        }.frame(width: 320, height: 240)
    }
}

The problem: the view insists on doing some dumb animation where the text is replaced with the new text, but truncated with ellipses, and it slowly expands widthwise until the entirety of the new text is shown.

Naturally, this is not an animation on opacity. It's not a frame width problem, as I've verified with drawing the borders.

Is this just another dumb bug in SwiftUI that i'm going to have to deal with, and pray that someone fixes it?

EDIT: ok, so thanks to @Mac3n, i got this inspiration, which works correctly, even if it's a little ugly:

Text(self.foozle)
    .frame(maxWidth: .infinity)
    .opacity(op)

Button(action: {
    withAnimation(.easeOut(duration: 0.3)) {
        self.op = 0

        DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) {
            self.foozle += "omo"

            withAnimation(.easeIn(duration: 0.3)) {
                self.op = 1
            }
        }
    }

}) {
    Text("ugh")
}

Theis Egeberg · Accepted Answer · 2020-04-19 14:25:53Z

8

The problem is that SwiftUI sees Text view as the same view. You can use the .id() method on the view to set it. In this case I've just set the value to a hash of the text itself, so if you change the text, the entire view will get replaced.

struct ContentView: View {
    @State var foozle: String = ""

    var body: some View {
        VStack() {
            Spacer()

            Text(self.foozle)
                .id(self.foozle.hashValue)
                .frame(maxWidth: .infinity)
                .transition(.opacity)

            Button(action: {
                withAnimation(.easeInOut(duration: 2)) {
                    self.foozle = "uuuuuuuuu"
                }
            }) { Text("ugh") }

            Spacer()
        }.frame(width: 320, height: 240)
    }
}

answered Apr 19, 2020 at 14:25

Theis Egeberg

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2 Comments

zhiayang Over a year ago

Oh, that's interesting to know! I'll try this out when I come back to this in a bit, but thanks for the answer!

Aviel Gross Over a year ago

Much more elegant, and the actual solution to the problem, instead of some hacky workaround. This should be the accepted answer.

Asperi · Accepted Answer · 2022-03-02 11:26:59Z

5

Transition works when view appeared/disappeared. In your use-case there is no such workflow.

Here is a demo of possible approach to hide/unhide text with opacity animation:

enter image description here

struct DemoTextOpacity: View {
    var foozle: String = "uuuuuuuuu"
    @State private var hidden = true

    var body: some View {
        VStack() {
            Spacer()

            Text(self.foozle)
                .frame(maxWidth: .infinity)
                .opacity(hidden ? 0 : 1)

            Button(action: {
                withAnimation(.easeInOut(duration: 2)) {
                    self.hidden.toggle()
                }
            }) { Text("ugh") }

            Spacer()
        }.frame(width: 320, height: 240)
    }
}

edited Mar 2, 2022 at 11:26

answered Feb 12, 2020 at 5:59

Asperi

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3 Comments

zhiayang Over a year ago

my usecase isn't really to hide/unhide text, rather the value of the Text needs to change, and i want it to change smoothly. that's all. the other answer below attempts to manually set the opacity to 0, change the text, then set it back to 1, but it does not work correctly.

Asperi Over a year ago

@zhiayang, Opacity as we as Transition are features of View (in your case Text) not of a model which in your case is String. If you animate changing string, SwfitUI animates appearance of string, letter by letter.

zhiayang Over a year ago

right, that makes sense i guess. it's not very intuitive. i found a solution, which i have edited in the question. thanks!

Mac3n · Accepted Answer · 2020-02-12 05:36:01Z

3

If you want to animate on opacity you need to change opacity value on your text element.

code example:

@State private var textValue: String = "Sample Data"
@State private var opacity: Double = 1
    var body: some View {
        VStack{
            Text("\(textValue)")
                .opacity(opacity)
            Button("Next") {
                withAnimation(.easeInOut(duration: 0.5), {
                    self.opacity = 0
                })
                self.textValue = "uuuuuuuuuuuuuuu"
                withAnimation(.easeInOut(duration: 1), {
                    self.opacity = 1
                })
            }
        }
    }

answered Feb 12, 2020 at 5:36

Mac3n

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3 Comments

zhiayang Over a year ago

this doesn't quite work; although the new text animates in, the old text simply disappears. the animation closure probably runs in a separate thread, and AFAIK there's no way to chain animations and no completion callback...

Mac3n Over a year ago

Maybe AnimatableModifire can do it. check this link : swiftui-lab.com/swiftui-animations-part3

zhiayang Over a year ago

this gave me the inspiration to reach a solution, so i'll accept this. thanks!

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