Source code for the article 'Stretchy header in SwiftUI' (https://jetrockets.pro/blog/stretchy-header-in-swiftui)

StretchyHeaderView.swift

//
//  ContentView.swift
//  StretchyHeader
//
//  Created by Alexey Belousov on 01.08.2019.
//  Copyright © 2019 JetRockets. All rights reserved.
//

import SwiftUI

let kImage = "example.image.from.assets"

let kTitle = "Stretchy header in SwiftUI"

let kPublishedAt = Date()

let kAuthor = "Author Name"

let kContent = """
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt 
ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco 
laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit 
in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat 
cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
"""

private let kHeaderHeight: CGFloat = 300

struct ContentView: View {
    
    private static let formatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateStyle = .short
        formatter.timeStyle = .short
        return formatter
    }()
    
    var body: some View {
        ScrollView {
            VStack(alignment: .leading) {
                GeometryReader { (geometry: GeometryProxy) in
                    if geometry.frame(in: .global).minY <= 0 {
                        Image(kImage).resizable()
                            .aspectRatio(contentMode: .fill)
                            .frame(width: geometry.size.width,
                                   height: geometry.size.height)
                    } else {
                        Image(kImage).resizable()
                            .aspectRatio(contentMode: .fill)
                            .offset(y: -geometry.frame(in: .global).minY)
                            .frame(width: geometry.size.width,
                                   height: geometry.size.height
                                    + geometry.frame(in: .global).minY)
                    }
                }.frame(maxHeight: kHeaderHeight)
                
                VStack(alignment: .leading, spacing: 8) {
                    HStack {
                        Text("\(kPublishedAt, formatter: Self.formatter)")
                            .foregroundColor(.secondary)
                            .font(.caption)

                        Spacer()

                        Text("Author: \(kAuthor)")
                            .foregroundColor(.secondary)
                            .font(.caption)
                    }

                    Text(kTitle)
                        .font(.headline)

                    Text(kContent)
                        .font(.body)
                }.frame(idealHeight: .greatestFiniteMagnitude)
                    .padding()
            }
        }.edgesIgnoringSafeArea(.top)
    }
    
}

#if DEBUG
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}
#endif