Android doesn’t deserve Swift… But we did it anyway 🤷

Talk given in NSSpain 2025

Transcript

1. Pierlugi Cifani, NSSpain 2025 Android doesn’t deserve Swift… …But we did it anyway 🤷
2. Ecce Homo
3. ✅
4. We should never compromise on excellence
5. Mobile Lead @ TheLeftBit I ’ m Pierluigi 👋 @piercifani @piercifani linkedin.com/in/pcifani theleftbit.com
6. Context • Small Software Studio • Specialized in Native Software
7. Random Prospect Client “But if we use \(CrossPlatformTech) it ’ s going to be cheaper”
13. Apps are no longer R+D
14. Apps are now Infrastructure
15. As demand for software exploded, apps could no longer be handcrafted.
18. Jeff Bezos “Your margin is my opportunity"
21. Apple Releases Swift as Open Source
22. + + +
23. What about the world’s most used OS?
24. Swift on Android Slow to non-existent progress during the first years • Community-led, not Apple-driven. • No official Android SDK for Swift exists. • Patches have to be applied on every official Swift Release to keep it compiling.
26. Foundation.framework UserDefaults Date Operation URLSession DateFormatter Calendar NotificationCenter JSONEncoder Data URL URLRequest FileManager Bundle Formatter Locale UUID OperationQueue ProcessInfo Timer IndexSet
27. And then…
31. • Toolchain built on top of the Open Source Swift project. • Allows you to write Android apps and libraries in Swift. • No compromise solution for iOS apps. • Not the only Swift-on-Android toolchain out there! Skip.tools
32. Transpiled Mode: 🔌 Transpile
33. Compiled Mode: Compiler 🛠 Bridging Code
34. So, can we use it?
35. • Projects are heavily modularized using SPM. • Swift 6 compatible. • Relies on Swift Concurrency: • No Combine or RxSwift • No GCD • No OperationQueue • Good candidate for Skip ’ s Compiled-mode Starting Point For Naturitas.app
36. This is our (Simplified) Build Graph For Naturitas.app
37. Starting Point Great code coverage!
38. Project “dibuix-lliure” began
39. $ skip android build
40. Build with the Skip Toolchain • Build the Module for macOS: • You ’ ll have IDE support. • Understand your dependencies. • Refactor UIKit or SwiftUI code out. First, macOS
41. $ git add . $ git commit -m “Refactor UIKit code out" $ git merge main
43. Build for Android $ skip android build
44. Build for Android • Most issues fall into three big buckets : • Open Source Foundation. • Non-compatible dependencies. • Wrapping Apple frameworks.
45. Build for Android 􀐚 FoundationNetworking 􀐚 FoundationEssentials 􀐚 FoundationInternationalization 􀐚 Foundation Open Source Foundation
46. import Foundation func sendNetworkRequest() async throws { let url = URL(string: "https://www.apple.com/iphone/")! let urlRequest = URLRequest(url: url) let _ = try await URLSession.shared.data(for: urlRequest) } Build for Android Open Source Foundation
47. import Foundation #if canImport(FoundationNetworking) import FoundationNetworking #endif func sendNetworkRequest() async throws { let url = URL(string: "https://www.apple.com/iphone/")! let urlRequest = URLRequest(url: url) let _ = try await URLSession.shared.data(for: urlRequest) } Build for Android Open Source Foundation
48. var targetDependencies: [Target.Dependency] = [ .product( name: "KeychainAccess", package: "KeychainAccess", ), ] Build for Android Non-compatible dependencies
49. var targetDependencies: [Target.Dependency] = [ .product( name: "KeychainAccess", package: "KeychainAccess", condition: .when(platforms: [.iOS]) ), ] Build for Android Non-compatible dependencies
50. import Foundation import CoreLocation class LocationFetcher: NSObject, CLLocationManagerDelegate {…} Build for Android Wrapping Apple platforms code
51. #if canImport(Darwin) import Foundation import CoreLocation class LocationFetcher: NSObject, CLLocationManagerDelegate {…} #endif Build for Android Wrapping Apple platforms code
52. Build for Android • At this point, the code should compile. • But runtime behavior of some classes is not guaranteed to be the same. • For example: UserDefaults does not persist it ’ s values. • Skip has Open Source packages to fill in the gaps. • Enter: Skip Fuse
53. import PackageDescription var packageDependencies: [Package.Dependency] = […] var targetDependencies: [Target.Dependency] = […]
54. import PackageDescription var packageDependencies: [Package.Dependency] = […] var targetDependencies: [Target.Dependency] = […] packageDependencies.append(contentsOf: [ .package(url: "https://source.skip.tools/skip-fuse.git"), ]) targetDependencies.append(contentsOf: [ .product(name: "SkipFuse", package: "skip-fuse"), ])
56. func userDefaults() -> UserDefaults { #if os(Android) SkipAndroidBridge.AndroidUserDefaults.standard #else UserDefaults.standard #endif } User Defaults
57. 🔥
59. Porting Swift Packages to Android
60. $ skip android export
61. Calling Swift from Kotlin • In order to call Swift code from Kotlin in Android Studio, we must first create JNI bindings. • WTF is JNI? • “It allows Java code that runs inside a Java Virtual Machine (VM) to interoperate with applications and libraries written in other programming languages”
62. Back to Xcode! packageDependencies.append(contentsOf: [ .package(url: "https://source.skip.tools/skip-fuse.git", from: "1.0.2"), ])
63. Back to Xcode! packageDependencies.append(contentsOf: [ .package(url: "https://source.skip.tools/skip.git", exact: "1.6.7"), .package(url: "https://source.skip.tools/skip-fuse.git", from: "1.0.2"), ])
64. Back to Xcode! var plugins: [Target.PluginUsage] = […] plugins.append(contentsOf: [ .plugin(name: "skipstone", package: "skip") ])
65. Back to Xcode!
66. Calling Swift from Kotlin • There are some limitations when creating Kotlin bridges for your Swift code: • Swift idioms that are not available on Kotlin • Skip limitations
67. Back to Xcode! public class Foo { public init() async throws { … } } Kotlin limitations
68. Back to Xcode! public class Foo { // SKIP @nobridge public init() async throws { … } } Kotlin limitations
69. Back to Xcode! public class Foo { // SKIP @nobridge public init() async throws { … } #if os(Android) public static func create() async throws -> Foo { return try await Foo() } #endif } Kotlin limitations
70. Skip limitations Back to Xcode!
71. Back to Exporting • All errors and warnings are cleared, call: skip export --module NaturitasCore \ -d android/lib/debug/ \ --project naturitas-core \ --no-export-project \ --debug \ --arch aarch64 --arch armv7 --arch x86_64
72. Back to Exporting 🔥
75. $ open /Applications/Android\ Studio.app
77. Android Studio • Based on JetBrain ’ s IntelliJ IDEA. • Installs the basic Android toolchain: • Java + Gradle • Android SDK • Emulators • Not AppKit-based, but Swing-Java based. • If you like “Mac-assed” apps, you ’ ll hate it. Everyone ’ s favorite IDE
78. Android Studio • Place the .aars generated by skip export somewhere where the Android codebase can reference it. • You can use: • Custom Maven repository • Github Packages • Merge the iOS and Android repositories • Storing .aars with Git LFS Let ’ s import the .aars
79. dependencies { // if you keep AARs under app/lib/debug implementation( fileTree( mapOf( "dir" to "../lib/debug", "include" to listOf("*.aar") ) ) ) }
80. Android Studio • Initialize Swift and Skip ’ s runtimes: And use the code! class MainActivity : ComponentActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) enableEdgeToEdge() setContent { … } } }
81. Android Studio • Initialize Swift and Skip ’ s runtimes: And use the code! class MainActivity : ComponentActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) skip.foundation.ProcessInfo.launch(this) enableEdgeToEdge() setContent { … } } }
82. Android Studio • Now import and use your Swift code from Kotlin! And use the code! import naturitas.core.AuthenticationManager val authManager = AuthenticationManager.create( apiClient = UserAPIClient.create(environment), socialNetworkTokenProvider = TokenRefresher() )
85. You can conform to Swift-protocols in Kotlin and inject those objects back into Swift!
87. Android Studio • There ’ s no throws in Java/Kotlin. Anything can throw so nothing throws. • Remember to try catch when the Swift code you ’ re calling can throw. • Add logging. A LOT. • You can ’ t add breakpoints inside any precompiled code; and your Swift Packages are integrated like that. Some tips
88. Android Studio • Do not expect deterministic memory behavior. • Java ’ s Garbage Collector can come and go whenever it wants. • Lots of patience when interacting with: • Hilt • Proguard Some tips
89. Android + Skip • Adds at least +50MB to the App ’ s Binary. • Iterate cycle depends on re-exporting the Swift codebase, which is slow. • Cultural friction. • Android Developers will complain. • It helped us the fact that I could put my thumb in the scale and make executive decisions. Tradeoffs
91. Android + Skip • URLSession has limits: • Bigger than usual errors where reported. • Based on libCURL • Not visible on Android Studio network debugger • We replaced it for an OKHTTP-based wrapper. Found issues
92. Android + Skip • All of the issues that you will encounter can be workaround or fixed. It ’ s just Swift code! • Dependencies can be forked and patched • Or even inverted! Conclusions
93. Android + Skip • We in the process of rewriting layer by layer the Naturitas app. • Replacing Kotlin-based subsystems by Swift-based subsystems. • Deeplinks, Push Notifications, Authentication and Remote Config ✅ • Networking and Data Validation ⏳ • Cart and Checkout ⏭ End result
94. But that’s not all…
96. 2X faster Time-to-Market for Android Features
97. And there’s more…
99. Common UI Elements AsyncButton("Hola 🇪🇸") { try await Task.sleep(for: .seconds(1)) } .buttonStyle(.borderedProminent)
100. Common UI Elements AsyncButton("Hola 🇪🇸") { try await Task.sleep(for: .seconds(1)) } .buttonStyle(.borderedProminent) .asyncButtonLoadingConfiguration( style: .inline(tint: .red) )
101. Common UI Elements AsyncButton("Hola 🇪🇸") { try await Task.sleep(for: .seconds(1)) } .buttonStyle(.borderedProminent) .asyncButtonLoadingConfiguration( style: .blocking( dimsBackground: true, successMessage: “Hecho” ) )
102. Common UI Elements @State var asyncViewID: String = "swap-1" VStack { Picker("Selection", selection: $asyncViewID) { … } .pickerStyle(.segmented) .padding(.horizontal) Spacer() AsyncView( id: $asyncViewID, dataGenerator: { try await generateData(asyncViewID) }, hostedViewGenerator: { ContentView(data: $0) } ) }
104. New clients! Without increasing the team size
105. Was it easy?
106. Was it easy? No
107. Was it worth it?
108. Was it worth it? Absolutely
109. Date.distantFuture
111. Apple has Open Sourced: - Swift Foundation - Swift Build - Swift Java - SourceKit LSP
112. • Partner with JetBrains to ensure Swift Package Manager integration is seamless across the IDE. • Collaborate with Google to minimize any binary size overhead when adding Swift to Android projects. • Keep investing in Swift-Java to make it the de- facto way to interoperate with JVM languages.
113. We as the Swift Community have a responsibility to be a beacon of excellence.
114. If we don ’ t succeed, the wrong tradeoffs will be forced on us.
115. Support the efforts to take Swift outside of the Apple ecosystem in any way that we can.
118. @ fi nagol fi n @vgorloff @andriydruk @compnerd @Obbut @aabewhite @etcwilde @Joannis @lhoward @marcprux Thank you!
119. Any questions?