matchedGeometryEffect 无法正常工作 [英] matchedGeometryEffect doesn't work properly

问题描述

使用此 Hacking with swift 文章，您会发现当 isZoomed 切换为 false 时，文本的动画效果不佳.我不明白为什么...

Using the last example from this Hacking with swift article you'll see that the text is not well animated when isZoomed is toggled to false. I can't understand why...

struct ContentView: View {
    @Namespace private var animation
    @State private var isZoomed = false

    var frame: CGFloat {
        isZoomed ? 300 : 44
    }

    var body: some View {
        VStack {
            Spacer()

            VStack {
                HStack {
                    RoundedRectangle(cornerRadius: 10)
                        .fill(Color.blue)
                        .frame(width: frame, height: frame)
                        .padding(.top, isZoomed ? 20 : 0)

                    if isZoomed == false {
                        Text("Taylor Swift – 1989")
                            .matchedGeometryEffect(id: "AlbumTitle", in: animation)
                            .font(.headline)
                        Spacer()
                    }
                }

                if isZoomed == true {
                    Text("Taylor Swift – 1989")
                        .matchedGeometryEffect(id: "AlbumTitle", in: animation)
                        .font(.headline)
                        .padding(.bottom, 60)
                    Spacer()
                }
            }
            .onTapGesture {
                withAnimation(.spring()) {
                    self.isZoomed.toggle()
                }
            }
            .padding()
            .frame(maxWidth: .infinity)
            .frame(height: isZoomed ? 400 : 60)
            .background(Color(white: 0.9))
        }
    }
}

推荐答案

将每个可移除的部分包裹到自己的堆栈中，容器将动画正确移除视图.

Wrap every removable part into own stack, the container will animation removing views properly.

使用 Xcode 12.1/iOS 14.1 测试

Tested with Xcode 12.1 / iOS 14.1

VStack {
    HStack {
        RoundedRectangle(cornerRadius: 10)
            .fill(Color.blue)
            .frame(width: frame, height: frame)
            .padding(.top, isZoomed ? 20 : 0)
        
        HStack {                         // << here !!
            if isZoomed == false {
                Text("Taylor Swift – 1989")
                    .matchedGeometryEffect(id: "AlbumTitle", in: animation)
                    .font(.headline)
                Spacer()
            }}
    }
    VStack {                             // << here !!
        if isZoomed == true {
            Text("Taylor Swift – 1989")
                .matchedGeometryEffect(id: "AlbumTitle", in: animation)
                .font(.headline)
                .padding(.bottom, 60)
            Spacer()
        }
    }
}

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