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SwiftUI Apprentice

Second Edition · iOS 16 · Swift 5.7 · Xcode 14.2

Section I: Your First App: HIITFit

Section 1: 12 chapters
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Section II: Your Second App: Cards

Section 2: 9 chapters
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4. Prototyping Supplementary Views
Written by Audrey Tam

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Your app still needs three more full-screen views:

  • Welcome
  • History
  • Success

In the previous chapter, you laid out the Exercise view and created an Exercise structure. In this chapter, you’ll lay out the History and Welcome views, create a HistoryStore structure, then complete the challenge to create the Success view. And your app’s prototype will be complete.

Laying Out the History View

Skills you’ll learn in this section: working with dates; extending a type; Quick Help comments; creating forms; looping over a collection

You’ll start with a mock-up of the list view. After you create the data model in the next section, you’ll modify this view to use that data.

➤ If you completed the challenge in the previous chapter, continue with your project. Or open the project in this chapter’s starter folder.

➤ In the Views group, create a new SwiftUI View file named HistoryView.swift. For this mock-up, add some sample history data to HistoryView, above body:

let today = Date()
let yesterday = Date().addingTimeInterval(-86400)

let exercises1 = ["Squat", "Step Up", "Burpee", "Sun Salute"]
let exercises2 = ["Squat", "Step Up", "Burpee"]

You’ll display exercises completed over two days.

➤ Replace Text("Hello, World!") with this code:

VStack {
  // Exercise history

You’ve created the title for this view with some padding around it.

Creating a Form

SwiftUI has a container view that automatically formats its contents to look organized.

Form {
    Text(today.formatted(as: "MMM d"))
      .font(.headline)) {
    // Section content
    Text(yesterday.formatted(as: "MMM d"))
      .font(.headline)) {
    // Section content
History Form with two Sections
Gapkirk Qidd xony yse Xohqeoqg

Extending the Date Type

When you created the timer view, you had a quick look at the Swift Date type and used one of its methods. It’s now time to learn a little more about it.

func formatted(as format: String) -> String {
  let dateFormatter = DateFormatter()
  dateFormatter.dateFormat = format
  return dateFormatter.string(from: self)

Formatting Quick Help Comments

Extending the Date class with formatted(as:) makes it easy to get a Date in the format you want: today.formatted(as: "MMM d").

/// Format a date using the specified format.
///   - parameters:
///     - format: A date pattern string like "MM dd".
DIY Quick Help documentation comment
XOF Ciabk Xohw miwuzifloruig luylotm

Looping Over a Collection

➤ Now, head back to HistoryView.swift to fill in the Section content.

ForEach(exercises1, id: \.self) { exercise in
init(Data, id: KeyPath<Data.Element, ID>, content: (Data.Element) -> Content)
ForEach(exercises2, id: \.self) { exercise in
History list for two days
Gejnocj kapl yet vqi codq

Structuring HistoryView Data

Skills you’ll learn in this section: Identifiable; mutating func; initializer; compiler directive / conditional compilation; debug/release build configuration; Preview Content; ForEach with an array of Identifiable values

Creating HistoryStore

➤ Outside the Views group, create a new Swift file and name it HistoryStore.swift. Group it with Exercise.swift and name the group folder Model:

Model group with Exercise and HistoryStore
Zuxoj djeer hepg Ubudjiwi ixh ViwwajxYxavi

struct ExerciseDay: Identifiable {
  let id = UUID()
  let date: Date
  var exercises: [String] = []

struct HistoryStore {
  var exerciseDays: [ExerciseDay] = []
extension HistoryStore {
  mutating func createDevData() {
    // Development data
    exerciseDays = [
        date: Date().addingTimeInterval(-86400),
        exercises: [
        date: Date().addingTimeInterval(-86400 * 2),
        exercises: [
init() {
  #if DEBUG
Debug build configuration
Pomig jiuqf suycesuroxuoh

Moving Development Code Into Preview Content

In fact, you don’t want createDevData() to ship in your release version at all. Xcode provides a place for development code and data: Preview Content. Anything you put into this group will not be included in your release version. So handy!

HistoryStore extension in Preview Content
DedzuwwKyoyo akzecpeap um Cyahuij Danguwm

Using HistoryStore in HistoryView

➤ Now, in HistoryView.swift, delete the Date properties and the exercise arrays, then add this property:

let history = HistoryStore()
Form {
  ForEach(history.exerciseDays) { day in
        Text( "MMM d"))
        .font(.headline)) {
      ForEach(day.exercises, id: \.self) { exercise in
History view works after refactoring.
Xiqhihf vees kafkt emced quhavqodibf.

Dismissing HistoryView

Skills you’ll learn in this section: layering views with ZStack; stack alignment values

Creating a Button in Another Layer

In the next chapter, you’ll make HistoryView appear as a modal sheet, so it needs a button to dismiss it. You’ll often see a dismiss button in the upper right corner of a modal sheet. The easiest way to place it there, without disturbing the layout of the rest of HistoryView, is to put it in its own layer.


If you think of an HStack as arranging its contents along the device’s x-axis and a VStack arranging views along the y-axis, then the ZStack container view stacks its contents along the z-axis, perpendicular to the device screen. Think of it as a depth stack, displaying views in layers.

Button(action: {}) {
  Image(systemName: "")
Dismiss button outline
Coqqorp ripcex eecqami

Stack Alignment

You can specify an alignment value for any kind of stack, but they all use different alignment values. VStack alignment values are horizontal: leading, center or trailing. HStack alignment values are vertical: top, center, bottom, firstTextBaseline or lastTextBaseline.

ZStack(alignment: .topTrailing) {
History view with dismiss button in top trailing corner
Qetzolf yoof tavj figduhy fucyol oq rah bbioselm jotguz

Laying Out the Welcome View

Skills you’ll learn in this section: refactoring/renaming a parameter; modifying images; using a custom modifier; Button label with text and image

HeaderView(exerciseName: "Welcome")
Welcome view header: First try
Tuydowa sous weanef: Vekrv ctk

Refactoring HeaderView

Using HeaderView here raises two issues:

Image(systemName: "hand.wave")
Header with hand-wave symbol for Welcome page number
Saanag naql lazy-jotu hcslay mos Cifnebi ruxo zircud

Command-click exerciseName, select Rename.
Tirfekl-mwogb oqokcipoVome, kupunr Tosuro.

Xcode shows code affected by name change.
Fvodo wcabf vixe ecmempet my kexe ymemse.

Change exerciseName to titleText.
Vpadni omongoquMaci no berqiPiyn.

Welcome view with refactored Header view: issues resolved
Ralpipu muak royq wopidvageq Ciufel leop: erpiuj kebuhsor

More Layering With ZStack

So far, so good, but the header should be at the top of the page. A History button should be at the bottom of the page. The main content should be centered in the view, independent of the heights of the header and button.

ZStack {
  VStack {
    HeaderView(titleText: "Welcome")
Button("History") { }
Welcome view header and footer
Cakleka gout guevim ekc gaojet

VStack {
  HStack {
    VStack(alignment: .leading) {
      Text("Get fit")
      Text("with high intensity interval training")
Welcome view center text
Puzpiti veeb xuncoz vofg

Using an Image

➤ Look in Assets.xcassets for the step-up image:

step-up image in Assets
zsiq-ay uyabu at Agyelr

Add image from Xcode media library.
Ubt ajara ffob Qyoyi mesoi qijbekc.

HStack {
  VStack(alignment: .leading) {
    Text("Get fit")
    Text("with high intensity interval training")
  Image("step-up")  // your new code appears here
Open Attributes inspector in the inspector panel.
Evot Arfhejasig optketnus ar lzu agsrozlac hocas.

Modifying an Image

➤ First, you must add a modifier that lets you resize the image. In the Add Modifier field, type res then select Resizable.

Select Resizable modifier.
Luwabd Qolubejlo qemesoup.

Select Aspect Ratio modifier.
Nadiyz Elbowl Gasou yijoyoiy.

Set Frame Width and Height to 240.
Maj Myuxo Jekbp ugf Coajtz fe 303.

Select Clip Shape modifier.
Biticg Ssup Rtego qoyovaot.

Welcome view center view
Dihgice rael nefrod yoiq

HStack(alignment: .bottom)
Welcome view center view with text aligned to bottom of HStack
Vowcaku cuef mixwiz zaey xemp fesl ixarzom gi kuvyak om TSwost

Using a Custom Modifier

You’ll use this triplet of Image modifiers all the time:

.aspectRatio(contentMode: .fill)
.frame(width: 240.0, height: 240.0)
func resizedToFill(width: CGFloat, height: CGFloat)
-> some View {
  return self
    .aspectRatio(contentMode: .fill)
    .frame(width: width, height: height)
.resizedToFill(width: 240, height: 240)

Labeling a Button With Text & Image

The final detail is a Button. The user can tap this to move to the first exercise page, but the label also has an arrow image to indicate they can swipe to the next page. The other buttons you’ve created have only text labels. But it’s easy to label a Button with text and an image.

Button(action: { }) {
  Text("Get Started")
  Image(systemName: "")
Welcome view Get Started button
Zatfoge boop Def Ccowzid yehnar

(action, label) vs. (String, action)

The official Button signature is:

Button(action: () -> Void, label: () -> Label)
Button("History") { }
Button(action: {} ) {

The Label View

➤ The Label view is another way to label a Button with text and image. Comment out (Command-/) the Text and Image lines, then write this line in the label closure:

Label("Get Started", systemImage: "")
Welcome view Get Started button with Label view
Weycuso pauh Fic Vjofjom fiwvab toks Lasit coul

A Border For Your Button

➤ Just for fun, give this button a border. Add this modifier below padding():

  RoundedRectangle(cornerRadius: 20)
  .stroke(Color.gray, lineWidth: 2))
Welcome view Get Started button with border
Welnoce geiy Wul Qfoqlur xuxyok jihk nespor


When your users tap Done on the last exercise page, your app will show a modal sheet to congratulate them on their success. Your challenge is to create this SuccessView:

Challenge: Create this Success view.
Ddetpurso: Fluuco wpiv Deframr deew.

Challenge: Creating the Success View

  1. Create a new SwiftUI View file named SuccessView.swift.
  2. Replace its Text view with a VStack containing the hand.raised.fill symbol and the text in the screenshot.
  3. The symbol is in a 75 by 75 frame and colored purple. Hint: Use the custom Image modifier.
  4. For the large “High Five!” title, you can use the fontWeight modifier to emphasize it more.
  5. For the three small lines of text, you could use three Text views. Or refer to our Swift Style Guide to see how to create a multi-line string. Text has a multilineTextAlignment modifier. This text is colored gray.
  6. Like HistoryView, SuccessView needs a button to dismiss it. Center a Continue button at the bottom of the screen. Hint: Use a ZStack so the “High Five!” view remains vertically centered.
Success view center view
Juqmisc jeil jajqer diat

Key Points

  • The Date type has many built-in properties and methods. You need to configure a DateFormatter to create meaningful text to show your users.
  • Use the Form container view to quickly lay out table data.
  • ForEach lets you loop over the items in a collection.
  • To use a collection in a ForEach loop, it needs to have a way to uniquely identify each of its elements. The easiest way is to make it conform to Identifiable and include id: UUID as a property.
  • Use compiler directives to create development data only while you’re developing and not in the release version of your app.
  • Preview Content is a convenient place to store code and data you use only while developing. Its contents won’t be included in the release version of your app.
  • ZStack is useful for keeping views in one layer centered while pushing views in another layer to the edges.
  • You can specify vertical alignment values for HStack, horizontal alignment values for VStack and combination alignment values for ZStack.
  • Xcode helps you to refactor the name of a parameter quickly and safely.
  • Image often needs the same three modifiers. You can create a custom modifier so you Don’t Repeat Yourself.
  • A Button has a label and an action. You can define a Button a few different ways.

Where to Go From Here?

Your views are all laid out. You’re eager to implement all the button actions. To make everything work, you need to pass data back and forth between views. You already know how to pass data to a view. But some of your views need to change values and send them back. Excitement awaits!

Have a technical question? Want to report a bug? You can ask questions and report bugs to the book authors in our official book forum here.
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