ContentView.swift

//
//  ContentView.swift
//  Layout
//
//  Created by Matt Gallagher on 7/6/19.
//  Copyright © 2019 Matt Gallagher. All rights reserved.
//

import SwiftUI

struct RowFrames: PreferenceKey {
	static var defaultValue: [Anchor<CGRect>] { return [] }
	static func reduce(value: inout [Anchor<CGRect>], nextValue: () -> [Anchor<CGRect>]) {
		value.append(contentsOf: nextValue())
	}
}

struct Row: View {
	let text: Text
	var body: some View {
		text.color(.white).padding().anchorPreference(key: RowFrames.self, value: .bounds) { [$0] }
	}
}

struct LeftColumn: View {
	var body: some View {
		VStack {
			Text("Shrink to fit column").fontWeight(.heavy)
			Row(text: Text("I'd really like these"))
			Row(text: Text("Blue"))
			Row(text: Text("Backgrounds"))
			Row(text: Text("To fill"))
			Row(text: Text("The width of this column"))
			Spacer()
		}.backgroundPreferenceValue(RowFrames.self) { value in
			GeometryReader { geometry in
				ZStack {
					ForEach(0..<value.count) { i in
						RoundedRectangle(cornerRadius: 8)
							.fill(Color.blue)
							.offset(x: 0, y: geometry[value[i]].origin.y)
							.frame(width: geometry.size.width, height: geometry[value[i]].size.height)
							.fixedSize()
					}
				}
			}
		}.padding().background(Color(appearanceName: .quaternaryLabel))
	}
}

struct ContentView : View {
	var body: some View {
		HStack(spacing: 0) {
			LeftColumn()
			GeometryReader { geometry in
				ScrollView {
					VStack(alignment: .leading, spacing: 8) {
						Text("A description of the problem").fontWeight(.heavy)
						Text("""
							Finally made a vertical-only scroll view. This area is \
							fixed to the width of the containing scroll view.
							
							The VStack column on the left of this ContentView is sized \
							to fit the widest text label plus padding, but no larger \
							(shrink to fit). This layout is tricky in SwiftUI but I \
							think there's a better approach than I'm using. Still it \
							reveals a few tricks that you can use in SwiftUI.
							"""
						).lineLimit(nil)
						Spacer()
					}.padding().frame(maxWidth: geometry.size.width, minHeight: geometry.size.height)
				}
			}
		}
	}
}

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