How to Implement Pull to Reveal in SwiftUI

import SwiftUI

// MARK: – PreferenceKey

private struct ScrollOffsetKey: PreferenceKey {
    static let defaultValue: CGFloat = 0
    static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
        value = nextValue()
    }
}

// MARK: – Revealed Banner

private struct RevealedBanner: View {
    var body: some View {
        HStack(spacing: 12) {
            Image(systemName: "bell.badge.fill")
                .foregroundStyle(.orange)
                .font(.title2)
            VStack(alignment: .leading, spacing: 2) {
                Text("Notifications")
                    .font(.headline)
                Text("3 unread alerts")
                    .font(.subheadline)
                    .foregroundStyle(.secondary)
            }
            Spacer()
            Button("View all") { }
                .buttonStyle(.bordered)
                .controlSize(.small)
        }
        .padding()
        .background(.regularMaterial, in: RoundedRectangle(cornerRadius: 16))
        .padding(.horizontal)
        .padding(.top, 8)
        .accessibilityElement(children: .combine)
        .accessibilityLabel("Notifications panel. 3 unread alerts.")
    }
}

// MARK: – Main View

struct PullToRevealView: View {
    @State private var revealed = false

    private let openThreshold: CGFloat  = 60
    private let closeThreshold: CGFloat = 10

    var body: some View {
        NavigationStack {
            ScrollView {
                // Zero-height sentinel — must be first child
                GeometryReader { proxy in
                    Color.clear.preference(
                        key: ScrollOffsetKey.self,
                        value: proxy.frame(in: .named("scroll")).minY
                    )
                }
                .frame(height: 0)

                LazyVStack(spacing: 0) {
                    // Revealed panel slides in above main content
                    if revealed {
                        RevealedBanner()
                            .transition(
                                .asymmetric(
                                    insertion: .move(edge: .top).combined(with: .opacity),
                                    removal:   .move(edge: .top).combined(with: .opacity)
                                )
                            )
                            .padding(.bottom, 8)
                    }

                    ForEach(1...30, id: \.self) { index in
                        HStack {
                            Image(systemName: "doc.text")
                                .foregroundStyle(.secondary)
                                .frame(width: 36)
                            Text("Row \(index)")
                                .frame(maxWidth: .infinity, alignment: .leading)
                        }
                        .padding()
                        .background(Color(.systemBackground))
                        Divider().padding(.leading, 52)
                    }
                }
            }
            .coordinateSpace(name: "scroll")
            .onPreferenceChange(ScrollOffsetKey.self) { offset in
                withAnimation(.spring(response: 0.4, dampingFraction: 0.8)) {
                    if !revealed, offset > openThreshold {
                        revealed = true
                    } else if revealed, offset < closeThreshold {
                        revealed = false
                    }
                }
            }
            .navigationTitle("Pull to Reveal")
            .navigationBarTitleDisplayMode(.inline)
        }
    }
}

// MARK: – Preview

#Preview {
    PullToRevealView()
}