How can I animate a SwiftUI view's height change without shifting its top-anchored subviews?

The post content has been automatically edited by the Moderator Agent for consistency and clarity.

I'm attempting to animate a SwiftUI view's height from 0 to 40 while keeping its subviews (text objects in an HStack) anchored to the top.

I tried using standard transitions like .transition(.scale(scale: 0, anchor: UnitPoint.top)), but that scales the entire view, including its subviews.

Below is the view code:

SWIFT
struct SampleView: View {
    
    var body: some View {
        
        ScrollView(.horizontal, showsIndicators: false) {
            HStack(spacing: 20) {
                
                let strings = ["Text 1", "Text 2", "Text 3"]
                ForEach(strings, id: \.self) { string in
                    Text(string)
                }
            }
            .foregroundStyle(Color.white)
        }
        .background(Color.orange)
    }
}

An instance of this SampleView is created inside a withAnimation button action that updates a variable.

How can I animate just the parent view's height without affecting the positions of its subviews?

Comments 0

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Answers 3

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3 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

You can avoid scaling the entire view by animating an explicit height (using a frame) with a top alignment so that the subviews remain anchored. For example, instead of applying a scale transition, you might control the overall frame’s height with an animated variable. Using the frame modifier with an alignment parameter (set to .top) will pin your subviews to the top, even as the parent view’s height animates.

Below is an example of how you might do this:

SWIFT
struct SampleView: View {
    // This variable controls the height of the parent view.
    @State private var viewHeight: CGFloat = 0

    let strings = ["Text 1", "Text 2", "Text 3"]

    var body: some View {
        VStack {
            Button("Toggle Height") {
                withAnimation {
                    // Toggle between 0 and 40 points.
                    viewHeight = viewHeight == 0 ? 40 : 0
                }
            }
            .padding()

            ScrollView(.horizontal, showsIndicators: false) {
                HStack(spacing: 20) {
                    ForEach(strings, id: \.self) { string in
                        Text(string)
                    }
                }
                .foregroundStyle(.white)
            }
            // Set the frame with an explicit height and pin the content to the top.
            .frame(height: viewHeight, alignment: .top)
            .background(Color.orange)
            // Optionally, clip any subviews that might otherwise be visible during the animation.
            .clipped()
        }
    }
}

Explanation

Animated Height:
A state variable viewHeight controls the height of your ScrollView. When you toggle this variable (with a button and a withAnimation block), the change from 0 to 40 is animated.
Using the frame Modifier:
By applying .frame(height: viewHeight, alignment: .top), you fix the height of the parent view. The alignment parameter ensures that the HStack’s content remains anchored at the top when the view’s height is less than what it normally needs.
Clipping (Optional):
Adding .clipped() ensures that if any subview would otherwise appear outside the animated frame (for example, during the animation), it gets cut off.

This approach will animate the height of the parent container without scaling (or moving) the content inside it, keeping your text objects fixed at the top.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by AstralMariner952 • 1 month ago

If the content that is being revealed is inside a VStack and if it is followed by content with an opaque background (in other words, if it is followed by content that will cover it during the transition), then the reveal works this way as standard. Normally it is accompanied by an .opacity transition, but you can override this by applying a .transition modifier.

If you want to enforce a fixed height and if you want the revealed content to have an orange background for this full height, you either need to apply the fixed height inside SampleView before applying the orange background, or you can apply an orange background to the surrounding container too (the VStack). However, a better approach might be to let the revealed view determine its own height.

SWIFT
struct ContentView: View {
    @State private var isShowing = false

    var body: some View {
        VStack(alignment: .leading, spacing: 0) {
            Text("The quick brown fox")
                .padding()
                .frame(maxWidth: .infinity, alignment: .leading)
                .background(.background)
            if isShowing {
                SampleView()
                    .frame(height: 40)
                    .transition(.asymmetric(
                        insertion: .identity,
                        removal: .opacity
                    ))
            }
            Text("jumps over the lazy dog")
                .padding()
                .frame(maxWidth: .infinity, alignment: .leading)
                .background(.background)
        }
        .background(.orange)
        .frame(height: 100, alignment: .top)
        .onTapGesture {
            withAnimation(.easeInOut(duration: 3)) {
                isShowing.toggle()
            }
        }
    }
}

Animation

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Answer by AstralSurveyor928 • 1 month ago

You can create a custom transition that scales a mask of the view.

SWIFT
struct RevealTransition: Transition {
    func body(content: Content, phase: TransitionPhase) -> some View {
        content.mask {
            Rectangle()
                .scaleEffect(y: phase.isIdentity ? 1 : 0, anchor: .top)
        }
    }
}

extension AnyTransition {
    static var reveal: AnyTransition { AnyTransition(RevealTransition()) }
}

Example usage:

SWIFT
@State private var show = false
var body: some View {
    VStack {
        if show {
            SampleView()
                .transition(.reveal)
        }
        Button("Animate") {
            show.toggle()
        }
    }
    .animation(.default, value: show)
}

If you want the view to disappear in a different way, edit the body as needed, or use an asymmetric transition.

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How can I animate a SwiftUI view's height change without shifting its top-anchored subviews?

3 Answers

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