Working With Simulators

So far in these lessons, the apps run on the default simulator with the default target when you build and run. However, the simulator has many other things it can do to help you test your apps under different scenarios.

With the simulator, you can:

• Run your app on multiple devices in parallel if you want to test interaction.
• Run your app on devices or operating system versions you don’t own.
• Test push notifications without a network or server.
• Make screenshots and videos for your advertising and App Store marketing.
• Configure and save different simulators you can launch without Xcode to run your app.

Though this lesson focuses on iOS simulators, there are tvOS, watchOS, and visionOS simulators. All of Apple’s devices and desktops share core technologies. This means that as you write an app, it’s possible to build native versions of your app for each type of device using a single Xcode project.

When you write an iOS app, it’ll run on the iPhone and iPad. The Mac and visionOS devices will also emulate an iPad to run your app. However, by making a separate target or destination for Mac, visionOS, or tvOS, you can build your app so that the devices don’t use the iPad emulation.

When supporting multiple destinations, you can share code between the targets, and each target can have its own code. Usually, an app that supports multiple platforms shares networking and business logic code. Then, for each target, the UI code is specific to that device so that the app will look like it belongs on the device. You can’t add watchOS as a destination; you can only add it as a separate target.

For example, if you want to use SwiftUI on different platforms, you’ll create different destinations, and you can have giant #if statements in your View code so that different code will run for a view that needs to look different.

var body: some View {
#if os(macOS)
    //SwiftUI code appropriate for macOS goes here
#endif

#if os(iOS)
    //SwiftUI code for this same view but for iOS 
#endif
}

In the snippet above, two blocks of code can execute depending on which type of device runs the code.

For a regular iOS app, the image above shows the default supported destinations. Mac and Apple Vision will run this app using their iPad simulators. You don’t require any additional coding or code segmentation to run your app in these destinations. However, if you think your app isn’t appropriate for one of these destinations, or your testing reveals that it won’t work how you want, you can remove a destination. This will make it impossible to install this target of your app on that platform.

You can also support multiple platforms by creating multiple targets. Unlike supporting multiple destinations, you’ll now create separate executable files for each platform. Though they all begin from the same Xcode project, each app is treated as its own entity. It can have its own icon and name and must have its own bundle identifier.

You add a target to a project using File ▸ New ▸ Target… or by clicking the + button at the bottom of the list of targets on the project settings screen. The template screen resembles the one that appears when making a new, standalone project for that target. You’re creating multiple apps within one Xcode project.

When working with multiple targets, you specify which target each file in your project goes with. Each file can be a member of one or all of your targets.

In the image above, a tvOS target has been added to the project. In the Project navigator, a separate folder structure exists for the tvOS target. This is just for organizational purposes.

To add a file from the iOS target to the tvOS target, check the box in the File inspector. An entire file has to be added. If you have some code you want to add to a separate target, you’ll need to split it into multiple files.

Xcode offers a different simulator download for each device type or OS you want to support. You may recall at the beginning of these lessons that, when you downloaded Xcode, you had to download the iOS SDK separately.

A list of all the simulators you’ve downloaded appears in the Platforms section of the Xcode Settings window. You can get the latest version of any SDK and simulator you’ve never downloaded by clicking the Get button on its row. To download a new version of a simulator and SDK, you use the + in the lower left. Simulators take up a lot of disk space, so you can remove them using the - button.

In early 2024, the current version of iOS is 17.2, and the oldest iOS simulator you can download is iOS 15. Apple’s philosophy is that everyone should always be on the latest iOS version, and if your device no longer supports the latest version, you should get a new one. However, in the real world, people keep devices for a long time.

When you first build an app, you should release it targeting only the latest version or maybe the latest two. Over time, Apple will keep advancing, but you might have users who don’t upgrade, and you’ll need to figure out what you want to do about them.

If you have the disk space, it’s a good idea to maintain simulators for every OS you support. As Apple marches forward, they may stop offering an OS simulator before you’re ready. If you already have it downloaded, you’ve got a better chance of supporting your stubborn users.

If you’re going to support OS versions older than Xcode provides simulators for, you’ll need to find physical devices with the older OS installed on them. Xcode 15 has debug and build files back to iOS 12, but simulators only to iOS 15.

Making Simulators

When Xcode first starts, it creates a default set of simulators—one for every shipping device running the latest version of the OS. You can make as many more as your hard drives have space for. In the top-middle of Xcode, you’ll see the current device that Xcode will build for. Clicking that device shows a drop-down of all available locations for building and running your code.

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