Build an iOS App on Windows: First SwiftUI iOS App on iPhone
Last updated
You can build an iOS app on Windows starting from an empty SwiftUI project. Install KXBuild and the VS Code extension, create the project, and write a to-do list in three steps that adds, checks off and saves items to a file. Press F5 to run it on your iPhone with breakpoints, then share it through TestFlight or Ad Hoc. There’s no Hackintosh or rented cloud Mac to set up. It suits first-time iOS developers and takes about an hour.
You need three things before you start. An Apple Developer account to create certificates and provisioning profiles. An iPhone and a cable that carries data. A PC with KXBuild and the VS Code extension installed. If you haven’t installed them yet, follow the install page.
How do you create a SwiftUI project on Windows?
Use either of these.
- VS Code extension. Press Ctrl+Shift+P to open the Command Palette and run
KXBuild: New Project. Pick the “iOS App (SwiftUI)” template, enterMyTodoas the project name, change the bundle ID to your own reverse domain, for examplecom.yourname.mytodo, and choose a folder. When it’s done, choose “Open in New Window”. - Command line. Run the command below in PowerShell, then open
D:\projects\MyTodowith File > Open Folder… in VS Code.
1kxbuild project create -t app_swiftui -n MyTodo -b com.yourname.mytodo -o D:\projects
Once it’s open, the KXBuild view on the left lists the MyTodo project and an app target of the same name. The project has only three things. MyTodoApp.swift is the app entry point, ContentView.swift is the main screen, and Assets.xcassets holds the icon and colors. All the code below goes into ContentView.swift, so you don’t need to add new files to the project.
The bundle ID is your app’s unique identifier with Apple. You’ll use the same one later for the provisioning profile and the app record in App Store Connect, so settle on it now and don’t change it afterward.
Step 1: How do you build the list in SwiftUI?
Start with a read-only list with the data hard-coded. Replace the whole contents of ContentView.swift with this.
1import SwiftUI
2
3struct TodoItem: Identifiable, Codable {
4 var id = UUID()
5 var title: String
6 var done = false
7}
8
9struct ContentView: View {
10 @State private var items = [
11 TodoItem(title: "Buy milk"),
12 TodoItem(title: "Give the app a new icon"),
13 TodoItem(title: "Send the ipa to a coworker", done: true)
14 ]
15
16 var body: some View {
17 NavigationView {
18 List(items) { item in
19 HStack {
20 Image(systemName: item.done ? "checkmark.circle.fill" : "circle")
21 .foregroundColor(item.done ? .green : .secondary)
22 Text(item.title)
23 .strikethrough(item.done)
24 }
25 }
26 .navigationTitle("To-dos")
27 }
28 }
29}
TodoItem holds one to-do. Identifiable lets List tell the rows apart, and Codable is for saving to a file in step 3. Whenever an array marked @State changes, the view refreshes on its own.
As you type, you’ll see completion at work. After Text(item.title). you get modifiers such as strikethrough, font and foregroundColor, and the parameters of Image(systemName:) and the initializers of List complete too. Press F12 on your own types to go to the definition. Mistakes get a red squiggle, and the Problems panel has the full error message. Code completion takes a few seconds to start the first time you open a Swift file. If nothing completes, run KXBuild: Restart Code Completion from the Command Palette. For more, see Code completion and indexing.
How do you run the app on your iPhone?
The first time you run on a device, you need to do two things, put your certificate in place and connect the phone. After that, you only press F5.
Add your certificate
Running on a device needs an Apple Development certificate (.p12) and a Development provisioning profile (.mobileprovision) that includes the UDID of this phone. If you don’t have them, you can sign in to your developer account in Appuploader to create them, or export them from the keychain on a Mac. See Certificates and signing for the options. To find the phone’s UDID, connect it to your PC and run the command below. It’s the first column.
1kxdevice device list
Create a keychain folder in the project root and put both files in it. Then create password.properties with one line in the form file=password.
1development.p12=123456
The .gitignore that comes with the template already excludes the keychain folder, so your certificates won’t be committed.
Connect the phone
Connect the iPhone to your PC with the cable, then click it under the Device node in the KXBuild view to make it the current device. The first connection involves these steps. See Set up your device for details.
- If the device node says “click to set up”, click it to install the Apple device drivers. You’ll be asked for administrator permission once.
- When the phone shows Trust This Computer, unlock it and tap Trust.
- On the phone, turn on Settings > Privacy & Security > Developer Mode. The phone restarts once. The switch only appears after the phone has been connected to a computer.
- The first time you debug a given iOS version, device symbols (several GB) download automatically. This takes about ten minutes or more, and only happens once.
Press F5
Press F5. KXBuild builds, signs, installs and launches the app, then attaches the debugger. The three hard-coded to-dos appear on the phone. The build log is in Output > KXBuild, and compiler errors are in the Problems panel. Click one to jump to the line.
If launching fails, the notification tells you which step it stopped at. The most common cause is a provisioning profile that doesn’t include this phone’s UDID. Add the UDID to the profile, download it again and replace the old file in keychain. For other messages, see Run and debug.
Step 2: How do you add, delete and check off items?
Now make the list editable. Add a text field at the top, tap a row to toggle it done, swipe left to delete, and use the Edit button in the top-right corner to delete several at once. Replace ContentView with the version below and leave TodoItem as it is.
1struct ContentView: View {
2 @State private var items: [TodoItem] = []
3 @State private var newTitle = ""
4
5 var body: some View {
6 NavigationView {
7 List {
8 Section {
9 HStack {
10 TextField("New to-do", text: $newTitle)
11 .onSubmit(add)
12 Button("Add", action: add)
13 .disabled(newTitle.trimmingCharacters(in: .whitespaces).isEmpty)
14 }
15 }
16 Section {
17 ForEach($items) { $item in
18 Button {
19 item.done.toggle()
20 } label: {
21 HStack {
22 Image(systemName: item.done ? "checkmark.circle.fill" : "circle")
23 .foregroundColor(item.done ? .green : .secondary)
24 Text(item.title)
25 .strikethrough(item.done)
26 .foregroundColor(.primary)
27 }
28 }
29 }
30 .onDelete { offsets in
31 items.remove(atOffsets: offsets)
32 }
33 }
34 }
35 .navigationTitle("To-dos")
36 .toolbar { EditButton() }
37 }
38 }
39
40 private func add() {
41 let title = newTitle.trimmingCharacters(in: .whitespaces)
42 guard !title.isEmpty else { return }
43 items.append(TodoItem(title: title))
44 newTitle = ""
45 }
46}
ForEach($items) { $item in … } gives you a binding to each row, so item.done.toggle() changes that element of the array directly. onDelete handles both swipe to delete and deleting in edit mode.
After changing code, stop debugging (Shift+F5) and press F5 again. The Restart button on the debug toolbar doesn’t recompile.
Set a breakpoint and inspect variables
In add(), click to the left of the line number on the items.append(...) line. A red dot appears. Back on the phone, type a to-do and tap “Add”. The app pauses and VS Code switches to the Run and Debug view.
Variables on the left shows the value of title, and Call Stack shows how the call got there. Press F10 to step over one line and F5 to continue. You can type lldb commands in the Debug Console below, for example po title to print the current title. Output from print in your code appears in Output > KXBuild Console.
Step 3: How do you save the data to a file?
Right now the to-dos are gone when you close and reopen the app. Save the list as a JSON file in the app’s Documents folder, write it on every change, and read it back at launch.
Put the data and the file logic in a TodoStore so the view only displays. Add this class below TodoItem in ContentView.swift.
1final class TodoStore: ObservableObject {
2 @Published var items: [TodoItem] = [] {
3 didSet { save() }
4 }
5
6 private let fileURL = FileManager.default
7 .urls(for: .documentDirectory, in: .userDomainMask)[0]
8 .appendingPathComponent("todos.json")
9
10 init() {
11 if let data = try? Data(contentsOf: fileURL),
12 let saved = try? JSONDecoder().decode([TodoItem].self, from: data) {
13 items = saved
14 }
15 }
16
17 private func save() {
18 do {
19 let data = try JSONEncoder().encode(items)
20 try data.write(to: fileURL, options: .atomic)
21 } catch {
22 print("Save failed: \(error)")
23 }
24 }
25}
Then change four places in ContentView to use the store instead of the @State array.
1 @StateObject private var store = TodoStore() // replaces @State private var items
2 // …
3 ForEach($store.items) { $item in // was ForEach($items)
4 // …
5 store.items.remove(atOffsets: offsets) // in onDelete
6 // …
7 store.items.append(TodoItem(title: title)) // in add()
Changing the @Published array triggers didSet, so checking off, deleting and adding each write the file once. Assigning items inside init doesn’t trigger didSet, so reading the file at launch doesn’t write it straight back.
Press F5 again and add a few to-dos. Swipe the app away in the app switcher, open it again, and the data is still there. To confirm the file really gets written, set a breakpoint on the let data = … line in save() and check off a to-do. When it pauses, type po fileURL in the Debug Console to see the full path of the file in the app’s sandbox.
When your data is just a few switches and a string or two, @AppStorage("key") in UserDefaults is simpler. List data like to-dos fits better in a file, and it’s easier to move to Core Data or SwiftData later.
Where do you change the app name and icon?
The app shows up on the home screen as MyTodo by default. In the KXBuild view, right-click the target and choose “KXBuild: Edit Target Settings”. On the General page, change Display Name to “To-dos” and press Ctrl+S to save. The same page also has the version number and the minimum iOS version. For what each field means, see Project Settings Editor.
For the icon, open Assets.xcassets from the asset catalog node in the KXBuild view and drop a 1024×1024 image into AppIcon. The other sizes are generated for you. See Asset Catalog Editor. Press F5 once more to see the changes on the phone.
How do you share the .ipa with others?
A Debug build only installs on the phones listed in its provisioning profile. To let others install it, pick one of the options below depending on how many people there are and whether they’re nearby.
Send it to testers with TestFlight
Use TestFlight when testers aren’t nearby or there are many of them. They install the TestFlight app on their iPhone and install your app from the invitation. No UDIDs need to be registered.
Put an Apple Distribution certificate and an App Store provisioning profile in the keychain folder, and add a password line for it in password.properties. Then use either of these.
- VS Code extension. Run
KXBuild: Build for App Store (.ipa)from the Command Palette or the project’s right-click menu. - Command line. Run the command below in the project folder.
1kxbuild build .\MyTodo.xcodeproj -c Release --export app-store
When it’s done, you’ll find build\MyTodo.ipa in the project folder. Create the app in App Store Connect, upload the .ipa with Appuploader, and once it’s processed, add testers on the TestFlight tab. See Release and App Store submission for details.
Install it on coworkers’ phones with Ad Hoc
For a few fixed test devices, use Ad Hoc. Register your coworkers’ UDIDs on the developer website, create an Ad Hoc provisioning profile that includes those devices, put it in the keychain folder with the Distribution certificate, and build with --export ad-hoc. It’s fine if keychain also has an App Store profile, since --export ad-hoc only uses Ad Hoc profiles.
1kxbuild build .\MyTodo.xcodeproj -c Release --export ad-hoc
Connect your coworker’s phone to your PC and run the command below to install it.
1kxdevice install .\build\MyTodo.ipa
That’s the full loop to build an iOS app on Windows: write the SwiftUI views, debug on a real iPhone, store data locally and ship a Release build. Adding screens or network calls later is the same cycle in the same project: edit the code and press F5.
FAQ
Can SwiftUI code be written and compiled on Windows?
Yes. SwiftUI code is written, completed and compiled on Windows, and KXBuild builds it into an app that installs on an iPhone. The List, NavigationView, @State and @StateObject used in this to-do list are standard SwiftUI, and the same project compiles if a teammate opens it on a Mac.
Can I send the Debug build I’m testing to someone else?
No. A Debug build only installs on phones whose UDIDs are in the Development provisioning profile. To share it, build Release with an Apple Distribution certificate and use TestFlight or Ad Hoc. See iOS code signing on Windows to prepare the certificates.
Why doesn’t the phone show my code changes?
The Restart button on the debug toolbar doesn’t recompile. After editing Swift code, press Shift+F5 to stop debugging, then press F5 so KXBuild rebuilds, signs and reinstalls the app.
Where are the to-dos stored on the phone?
In todos.json in the Documents folder of the app’s sandbox. Deleting the app removes that folder and the data with it. Swiping the app away from the app switcher doesn’t affect it.