Disappearing Floating action button SwiftUI

FabDemo.swift

import SwiftUI
import Combine

struct ContentView: View {
    @State var showFab = true
    @State var scrollOffset: CGFloat = 0.00

    var body: some View {
        ScrollView {
            VStack (alignment: .leading) {
                ForEach(0..<30) { i in
                    HStack {
                        Text("Item \(i)").padding()
                        Spacer()
                    }
                }
            }.background(GeometryReader {
                return Color.clear.preference(key: ViewOffsetKey.self,
                                       value: -$0.frame(in: .named("scroll")).origin.y)
            })
            .onPreferenceChange(ViewOffsetKey.self) { offset in
                withAnimation {
                    if offset > 50 {
                        showFab = offset < scrollOffset
                    } else  {
                        showFab = true
                    }
                }
                scrollOffset = offset
            }
        }
        .coordinateSpace(name: "scroll")
        .overlay(
            showFab ?
                createFab()
                : nil
            , alignment: Alignment.bottomTrailing)
    }

    fileprivate func createFab() -> some View {
        return Button(action: {
        }, label: {
            Image(systemName: "plus")
                .font(.title)
                .foregroundColor(.white)
                .frame(width: 40, height: 40, alignment: .center)
        })
        .padding(8)
        .background(Color.blue)
        .cornerRadius(15)
        .padding(8)
        .shadow(radius: 3,
                x: 3,
                y: 3)
        .transition(.scale)
    }
}

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

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

I know its been a little while but to solve the over scroll issue I changed lines 21-31 to:

.onPreferenceChange(ViewOffsetKey.self) { offset in
 withAnimation {
  if offset < 50 {
   showFab = true
  } else  {
   showFab = false
  }
 }
}

Then it appears on when near the top and off once passed the scroll point.