A placeholder that expands to fill the remaining screen height

PlaceholderCell.swift

//  Created by Matt Comi on 12/8/21.

import SwiftUI

struct HeaderView: View {
  var body: some View {
    VStack(spacing: 6) {
      Text("Stampy").font(.title).foregroundColor(.purple).fontWeight(.heavy)
      Text("Your Digital Stamp Collection").font(.footnote).foregroundColor(.secondary)
    }
    .padding(32)
    .frame(maxWidth: .infinity, maxHeight: .infinity)
    .background(Color(UIColor.secondarySystemBackground))
    .mask(RoundedRectangle(cornerRadius: 20, style: .continuous))
    .padding(16)
  }
}

struct PlaceholderView: View {
  var body: some View {
    Text("Your Stamp Collection is Empty").foregroundColor(.secondary)
  }
}

struct HeightPreferenceKey: PreferenceKey {
  typealias Value = CGFloat
  static var defaultValue: Value = .zero
  static func reduce(value _: inout CGFloat, nextValue _: () -> CGFloat) {}
}

struct ContentView: View {
  @State var headerHeight: CGFloat = 0

  var body: some View {
    GeometryReader { screenGeo in
      ScrollView {
        VStack(spacing: 0) {
          HeaderView()
            .background(
              GeometryReader { geo in
                Color.clear.preference(key: HeightPreferenceKey.self, value: geo.size.height)
              }
            )
            .onPreferenceChange(HeightPreferenceKey.self) { value in
              headerHeight = value
            }
          PlaceholderView()
            .frame(height: screenGeo.size.height - headerHeight)
        }
      }
    }
  }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}