你的问题和代码表明你在这方面做了很多研究。不幸的是，您试图将您发现的所有内容合并到这一视图中。你遇到的第一个问题是你不能同时拥有一个垂直的ScrollView和一个垂直的DragGesture。这不管用第二，DragGestures和PreferenceKeys实际上不能像这样一起工作。在这种情况下，您甚至不需要DragGesture，只需要PreferenceKey。第三，不要在ScrollView中的视图上放置偏移量，否则会改变视图的垂直位置。如果DragGesture偶尔能工作，你的视图就会上下跳动。让ScrollView来处理这个问题。下面注解代码：

struct ScrollDownToHide: View {
    @State private var isCardVisible = true
    @State private var dragOffset: CGFloat = 0
    
    var body: some View {
        ZStack {
            Color.gray.ignoresSafeArea()
            
            if isCardVisible {
                ScrollView {
                    VStack(spacing: 20) {
                        Text("Card View")
                            .font(.largeTitle)
                            .padding()
                            .background(Color.white)
                            .cornerRadius(8)
                            // The GeometryReader needs to be on the card view itself.
                            // You need to know where card view is, not the
                            // ScrollView's location on the screen.
                            .overlay(
                                GeometryReader { geometry in
                                    Color.clear
                                        .preference(key: OffsetPreferenceKey.self, value: geometry.frame(in: .global).origin.y)
                                }
                            )
                            // This could have been anywhere in the view as long as it
                            // was on a visible view.
                            .onPreferenceChange(OffsetPreferenceKey.self) { value in
                                dragOffset = value
                            }
                    }
                    .padding()
                }
                // read the dragOffset in an `.onChange(of:)` to catch the updated values.
                // SwiftUI's origin in this case has (0,0) in the upper left
                // so origin.y will increase as the card goes down the screen.
                .onChange(of: dragOffset) { newValue in
                    if newValue > 200 {
                        withAnimation {
                            isCardVisible.toggle()
                        }
                    }
                }
            } else {
                Button("Show Card") {
                    isCardVisible = true
                }
                .padding()
                .foregroundColor(.white)
                .background(Color.blue)
                .cornerRadius(8)
            }
        }
    }
}

// With the PreferenceKey, you do not need the func reduce to do anything to the value,
// you are simply passing the y value along.
struct OffsetPreferenceKey: PreferenceKey {
    static var defaultValue: CGFloat = 0
    
    static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {}
}

最后，将卡片放回原处的实际动画被称为“英雄动画”，它使用MatchedGeometry效果。谷歌，你会发现很多关于使用它的教程。