All about Working with Xcode Previews

In the realm of iPhone app development, there exists a powerful yet elusive tool known as Xcode Previews. It holds the potential to revolutionize the way teams design, iterate, and test user interfaces. 

With its real-time feedback and dynamic visualization capabilities, Xcode Previews offer a glimpse into the future of app development. Its significance extends beyond just the industry leading Apple device and app ecosystem.

New iOS apps are released regularly with steady numbers every month which makes it essential to use XCode Previews to deliver high quality iOS apps.

Apple app release trends shows consistency and strong volumes

As Android and Web UI developers look at Xcode with envy and frustration, trying to find analogous features within their own ecosystems, they willingly or unwillingly give credence to the desirable features offered by Xcode Previews.

Let’s dive right into the details.

What is Xcode Previews?

Xcode Previews is a feature introduced in Xcode 11 +, Apple’s integrated development environment (IDE) for macOS, used for developing applications for Apple platforms i.e. iOS, iPadOS, macOS, watchOS and tvOS. 

Xcode Previews allows developers to see real-time previews of their user interfaces (UI) and interact with them directly in the Xcode editor without running the entire application as a finalized bundle (.ipa etc.).

With Xcode Previews, developers can create and modify SwiftUI views, which are user interface components, and see the changes immediately in the Preview canvas.

When to use Xcode Previews?

Xcode Previews can be used in various scenarios during the development of Apple platform applications. Here are a few situations where Xcode Previews can be particularly beneficial:

1. Building User Interfaces

• Xcode Previews is excellent for designing, coding, debugging and iterating on user interfaces (UIs). 
• It allows developers to see real-time visual representations of their UI components as they make changes. 
• This makes it easier to experiment with different layouts, colors, fonts, and other design elements, helping developers create aesthetically pleasing and user-friendly interfaces.

2. Dynamic UI Testing

• Xcode Previews enables developers to simulate different data states within their UI components. 
• By providing sample data or dynamically changing data inputs, developers can visualize how their UIs react to different scenarios without running the entire application. 
• This is particularly useful for testing edge cases, handling error conditions, or validating UI responsiveness.

3. Responsive Design

• With Xcode Previews, developers can preview their UIs across different devices and screen sizes. 
• This allows them to ensure that the UI components adapt well to various screen dimensions, orientations, and safe areas. 
• It helps developers identify and fix layout issues early in the development process, saving time and effort in later stages.

4. Rapid Prototyping

• Xcode Previews can be used for rapid prototyping of UI concepts. 
• Developers can quickly create and modify SwiftUI views, preview them in real-time, and experiment with different design ideas. 
• This facilitates faster exploration of UI options, enabling developers to iterate and refine their designs efficiently.
  

5. Collaboration 

• Xcode Previews provide a visual representation of UI designs, making it easier to collaborate with designers, product managers, and stakeholders. 
• It allows for quicker feedback cycles, as stakeholders can visually review and interact with the UI in the Xcode editor. 
• This fosters effective communication and alignment among team members.

Xcode Previews enhances productivity, speeds up the development cycle, and improves the overall quality of Apple platform applications.

How to use Xcode Previews?

Here are the ways that you can use to create XCode Previews, Work with the XCode Previews, and variations in XCode Previews.

Creating Previews

To create an Xcode preview you don’t have to perform extra steps.

1. Create a new Xcode project, or open an existing one.

2. The Project configuration window will show up.

3. Create a new SwiftUI file or open an existing one in Xcode.

At the bottom of the file, Xcode automatically inserts a preview structure. Configure this structure as needed. For Example, this is the default ‘View’ upon creating a new project inside Xcode:

import SwiftUI
struct ContentView: View {
    var body: some View {
        VStack {
            Image(systemName: “globe”)
                .imageScale(.large)
                .foregroundColor(.accentColor)
            Text(“Hello, world!”)
        }
        .padding()
    }
}
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

4. Preview can take few seconds or minutes to load, depending on your computer.

For the purpose of this demonstration, lets add a few UI components:

• A TextField/Input
• A Picker/Dropdown
• A Button

This is just to populate the screen (not worrying about functionality here). Updated ‘View’ becomes: 

import SwiftUI
struct ContentView: View {
    @State private var name: String = “”
    @State private var selectedOption: String = “”
    
    var body: some View {
        VStack {
            Image(systemName: “globe”)
                .imageScale(.large)
                .foregroundColor(.accentColor)
                .padding(.bottom, 20) // Update image position
            
            Text(“Hello, \(name)!”) // Update text
                .font(.largeTitle)
                .foregroundColor(.primary)
                .padding(.bottom, 20) // Update text position
            
            TextField(“Enter your name”, text: $name)
                .padding()
                .textFieldStyle(RoundedBorderTextFieldStyle())
                .padding(.bottom, 20) // Add input field
            
            Picker(“Select an option”, selection: $selectedOption) { // Add dropdown
                Text(“Option 1”).tag(“Option 1”)
                Text(“Option 2”).tag(“Option 2”)
                Text(“Option 3”).tag(“Option 3”)
            }
            .pickerStyle(SegmentedPickerStyle())
            .padding(.bottom, 20)
            
            Button(action: {
                // Add button action
            }) {
                Text(“Submit”)
                    .font(.headline)
                    .foregroundColor(.white)
                    .padding()
                    .background(Color.blue)
                    .cornerRadius(10)
            }
        }
        .padding()
    }
}

Working with Previews

Let’s add the following devices as previews inside our PreviewProvider: 

• iPhone 12
• iPad (9th generation)
• Apple Watch Series 7 – 45mm
• Apple TV

Updated ‘ContentView_Previews’ looks like this :

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        Group {
            ContentView()
                .previewDevice(PreviewDevice(rawValue: “iPhone 12”))
                .previewDisplayName(“iPhone 12”)
            
            ContentView()
                .previewDevice(PreviewDevice(rawValue: “iPad (9th generation)”))
                .previewDisplayName(“iPad”)
            
            ContentView()
                .previewDevice(PreviewDevice(rawValue: “Apple Watch Series 7 – 45mm”))
                .previewDisplayName(“Apple Watch”)
            
            ContentView()
                .previewDevice(PreviewDevice(rawValue: “Apple TV”))
                .previewDisplayName(“Apple TV”)
        }
    }
}

Please note that in order for these devices to actually work properly as previews, you need to add the right ‘Targets’ and download necessary files. 

Now consider you want to have views based on custom criteria, not limited to form-factors offered by Apple. For example, let’s add variations to manually adjust the previews for these scenarios:

• Size That Fits: Uses the .sizeThatFits layout to automatically size the preview based on its content.
• Custom Size: Uses the .fixed(width:height:) layout to specify a custom width and height for the preview.
• Landscape: Uses the .fixed(width:height:) layout to specify a custom width and height for the preview and also sets the previewInterfaceOrientation to .landscapeRight to show the view in landscape orientation.

Updated code:

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        Group {
            ContentView()
                .previewLayout(.sizeThatFits)
                .previewDisplayName(“Size That Fits”)
            
            ContentView()
                .previewLayout(.fixed(width: 400, height: 800))
                .previewDisplayName(“Custom Size”)
            
            ContentView()
                .previewLayout(.fixed(width: 800, height: 400))
                .previewInterfaceOrientation(.landscapeRight)
                .previewDisplayName(“Landscape”)
        }
    }
}

Variations in Previews

Additionally, here are some commonly occurring iPhone app UI development scenarios and techniques you can use with Xcode previews:

• Handling different screen sizes: To handle different screen sizes, you can use the previewLayout(_:) function to override the size of the container for the preview. For example, you can use .previewLayout(.fixed(width: 375, height: 667)) to simulate an iPhone 8 screen size.
• Simulating different device orientations: You can use the previewInterfaceOrientation(_:) function to override the orientation of the preview. For example, .previewInterfaceOrientation(.landscapeLeft) will display the preview in landscape orientation.
• Testing different color schemes: To test different color schemes, you can use the preferredColorScheme(_:) view modifier. For example, .preferredColorScheme(.dark) will simulate the dark color scheme.
• Handling dynamic type: If your app supports dynamic type, you can test how your views adapt to different text sizes. You can use the environment (\.sizeCategory, .accessibilityExtraExtraLarge) modifier to simulate larger text sizes.
• Previewing different data states: If your app’s UI varies based on different data states, you can use the @State property wrapper to simulate data changes in the preview. For example, you can use @State var isLoading: Bool = true to simulate loading state.
• Testing different localization: To test your app’s UI in different languages, you can use the LocalizablePreview struct. It allows you to preview localized strings by specifying the key and value pairs.
• Simulating different accessibility settings: You can use the accessibility* modifiers to simulate different accessibility settings in the preview. For example, .accessibilityDifferentiateWithoutColor(true) simulates the “Differentiate Without Color” accessibility setting.
• Combining views with Group: If you want to maintain multiple previews but apply a single modifier to all of them, you can use the Group view to wrap your previews.

These techniques will help you handle various scenarios and ensure that your app’s UI looks and behaves correctly on different devices, settings.

Please note that this was just a basic example of using Xcode Previews for iPhone App Development. 

Advantages of using Xcode Previews

Using the Xcode previews feature offers several advantages for developing iOS apps:

• Rapid iteration and feedback: Xcode previews allow you to see the visual representation of your UI components in real-time as you write and modify code.
• Enhanced productivity: With Xcode previews, you can work directly in the preview canvas without the need to constantly switch between the code editor and simulator, providing a focused environment for UI development.
• Isolation and independence: Previews provide a self-contained environment for testing and fine-tuning UI components. They are independent of the app’s runtime environment and dependencies.
• Simulating different configurations: Xcode previews allow you to simulate various configurations, including different devices, screen sizes, orientations, color schemes, accessibility settings, and data states.
• Testing edge cases and states: Previews enable you to test your UI components with different edge cases, such as empty states, error conditions, long text, and large data sets.
• Collaboration and communication: Xcode previews make it easier to share and discuss UI designs with team members or stakeholders. You can generate visual previews of your UI components and share them as images or live previews.
• Documentation and reference: Previews serve as a form of documentation for your UI components. By including previews in your codebase, you create a visual reference that helps you and other developers understand the intended appearance and behavior of the UI components.
• Simplifying UI testing: Xcode previews can be leveraged as a foundation for UI testing. By having well-defined previews, you can write UI tests that validate the correctness of your UI components easily.

Limitations of Xcode Previews

While Xcode previews offer many benefits, it’s important to be aware of their limitations:

• Limited runtime environment: Xcode previews simulate the appearance of your UI components but do not provide a full runtime environment. They may not accurately reflect certain runtime behaviors, such as animations, transitions, or complex interactions that rely on live data or network requests.
• Performance considerations: Previews are primarily focused on visualizing UI components and may not accurately represent the performance characteristics of your app.
• Dependency management: Previews might encounter difficulties when interacting with external dependencies or complex dependency graphs. If your UI components rely on specific dependencies or frameworks, it’s important to ensure that they are properly handled within the preview environment.
• Limited access to device-specific features: Previews do not have direct access to device-specific features, such as GPS, camera, or push notifications. If your UI components rely on these features, you may need to test them on actual devices or even better, BrowserStack Device cloud.

• Limited testing coverage: While Xcode previews help validate the visual aspects of your UI components, they do not replace comprehensive unit tests, integration tests, or end-to-end tests.
• Layout discrepancies: Although Xcode previews aim to simulate various screen sizes and orientations, there may be slight layout discrepancies between the preview canvas and the actual devices or simulators.
• Complex view hierarchies: Previews can become less efficient or slower to render when dealing with complex view hierarchies or computationally expensive layouts.
• Limited platform support: While Xcode previews support iOS, iPadOS, macOS, Mac Catalyst, tvOS, and watchOS, there may be certain platform-specific behaviors or APIs that are not accurately represented in the previews.

Despite these limitations, Xcode previews remain a valuable tool for visualizing and iterating on UI components during development. 

It’s recommended to combine previews with other testing techniques to achieve comprehensive coverage and ensure the overall quality of your app.

Testing Xcode Previews on real devices

Testing Xcode previews on real devices could be an expensive and time consuming task. But it is majorly simplified by BrowserStack’s Device Cloud and App Live services. Here’s how it can help teams better manage testing on real devices:

Test on Real Devices with BrowserStack App Live

• Setup and configuration: Upload your Application to BrowserStack cloud using one of these options.
• Device selection: With BrowserStack App Live, you gain access to a wide range of real devices, including iPhones and iPads, running different iOS versions. You can choose the specific device models and iOS versions you want to test your Xcode previews on.

• Interaction and navigation: App Live provides a live, interactive streaming of the chosen real device directly to your browser. This allows you to interact with a real device within your browser.

• Real-time debugging: App Live facilitates real-time debugging of your app UI by providing access to device logs, console outputs, and runtime errors. This helps in diagnosing and resolving any issues or errors that may arise during the testing process.

• Multi-device testing: BrowserStack App Live allows you to test Xcode previews across multiple real devices. This enables you to observe the consistency of your UI components across different devices versions and ensure a seamless user experience across a variety of screen sizes, resolutions, and orientations.

• Collaboration and sharing: With App Live, team members can collaborate effectively by sharing the live device stream with other stakeholders, including designers, developers, and QA testers. This enables everyone to provide feedback, discuss issues, and make informed decisions based on the actual behavior of the app.
• Cloud-based infrastructure: BrowserStack’s cloud-based infrastructure ensures that teams can test their app on a scalable and reliable platform. It eliminates the need for maintaining physical devices, reduces infrastructure costs, and allows for parallel testing across multiple devices, speeding up the testing process.
• Cross-platform testing: In addition to testing Xcode previews on iOS devices, BrowserStack App Live also supports testing on Android devices. This is particularly beneficial for teams working on cross-platform projects or developing web based apps that require compatibility across different operating systems.

Conclusion

Xcode previews offer powerful tools for iOS developers to design, iterate, and test UI. They provide real-time feedback, enhancing productivity. However, they have limitations and should be supplemented with other tests. 

BrowserStack App Live helps test previews on real devices, enabling interactive debugging, multi-device synchronization, and collaboration. It offers a scalable cloud-based infrastructure for all your app testing needs. 

Try BrowserStack App Live Now

Ultimately, Xcode Previews and App Live help streamline UI development, improve app quality, and deliver great user experiences on Apple devices.