Tips & Tricks

This page provides various tips, optimizations, and workarounds to help you get the most out of spm4Kmp.

Importing Swift Code into Kotlin

If you're looking for practical examples of how to bridge Swift and Kotlin, check out the dedicated playground repository.

The repository is regularly updated with new examples. Feedback and requests for specific use cases are always welcome!

Optimizing Build Performance

Reduce Build Time

By default, Swift Package Manager (SPM) working files are stored within the Gradle build folder. You can change this behavior using the spmWorkingPath property.

Example configuration in your build.gradle.kts:

swiftPackageConfig {
    // ...
    spmWorkingPath = "${projectDir.resolve("SPM")}"
}

CI/CD Caching

To speed up your CI/CD pipelines, ensure you cache the SPM working directory: - The default directory: build/spmKmpPlugin - Or your custom spmWorkingPath if set.

Implementing Firebase

Integrating Firebase into a KMP project can be complex. We provide a complete reference implementation to guide you.

Handling Objective-C Types (_objcnames.classes_)

When working with Objective-C types (like UIView, UIViewController, etc.), cinterop might occasionally need a "hint" to correctly map the types.

Example Solution

If cinterop fails to recognize a specific type, you can force its inclusion by creating a dummy Swift class or using NSObject as a bridge.

import UIKit

// Option 1: Force cinterop to include `platform.UIKit.UIView` via a dummy class
@objcMembers public class MyDummyView: UIView {}

// Option 2: Use inheritance or explicit NSObject mapping
@objcMembers public class TestClass: NSObject {

    // Simply returning `UIView` may not always be enough for cinterop
    public func getView() -> UIView {
        return UIView()
    }

    // Using NSObject can sometimes be more reliable for mapping
    public func getViewWithNSObject() -> NSObject {
        return UIView()
    }
}

import platform.UIKit.UIView

// In your Kotlin code:
fun getView(): UIView = TestClass().getView()

// Or with explicit casting if using the NSObject approach:
fun getViewCasted(): UIView = TestClass().getViewWithNSObject() as UIView

Custom Swift Versions & Toolchains

The plugin uses the system Swift command directly. If you need to support older Xcode versions or specific Swift toolchains, you can customize the binary path.

Using swiftly

We recommend using swiftly to manage multiple Swift versions on macOS.

1. Install the desired Swift version via swiftly.
2. Set the swiftBinPath in your configuration:

spm {
    // ...
    swiftBinPath = "/path/to/.swiftly/bin/swift"
}

Swift Concurrency in iOS Tests

If your bridge uses async/await and you encounter errors during KMP tests (e.g., Library not loaded: libswift_Concurrency.dylib), it's likely due to the minimum deployment target.

The Problem

Kotlin Multiplatform tests often default to a low minimum target (e.g., iOS 12/14), while Swift Concurrency requires iOS 15.0+.

The Fix

Override the minimum OS version for your test binaries:

kotlin {
    iosSimulatorArm64().binaries.getTest("debug").apply {
        freeCompilerArgs += listOf(
            "-Xoverride-konan-properties=osVersionMin.ios_simulator_arm64=16.0",
        )
    }
}

Disabling Automatic IDE Package Resolution

If your project contains a Package.swift manifest, IntelliJ/Android Studio might attempt to resolve it automatically. This can slow down the IDE and consume unnecessary disk space.

After disabling this, you can safely reclaim disk space by deleting: ~/Library/Caches/JetBrains/IntelliJIdea[Version]/DerivedData

Enabling Execution Tracing

To debug performance or execution flow, you can enable detailed tracing.

1. Add the following flag to your gradle.properties:

   spmforkmp.enableTracing=true
   

2. Find the generated traces in the spmForKmpTrace directory.