SwiftUI Previews don't Work for Kotlin Multiplatform Mobile (KMM) Projects.

Today, I encountered a problem in a KMM project where the SwiftUI preview didn't work. I joined the project after most of the functionality was complete. I needed to add some UI components on the iOS side, but all preview configurations for views failed, and I received an error message in the left panel of Xcode.

I could proceed without the preview display, but it was highly inefficient, especially for someone new to SwiftUI. I began investigating the problem. The key issue was that I needed some classes from a shared module, but they weren't recognized by Xcode. I looked deeper into the Gradle configuration for the shared part. The solution involved changing the static parameter from true to false.

iosTarget.binaries.framework {
    baseName = "Shared"
    isStatic = true
}

So, what is the role of this, and how does it affect the SwiftUI preview? After googling and conversing with various LLMs, I found out that it determines whether the framework will be a static or a dynamic framework.

• Static linking is used: All code from the framework is linked into the final app binary at compile time. This avoids the need for dynamic loading at runtime.
• Dynamic linking is used: The framework is included as a separate .framework file in the app bundle and is loaded into memory at runtime.
• Dynamic frameworks are loaded at runtime, which aligns well with how SwiftUI previews function. Previews are executed in a separate runtime environment (a simulator process) and rely on dynamic loading of the compiled code to render live updates.

As a result, I set static = false while developing new functionality and change it to static = true when building and distributing applications. I hope this information will help you save several hours if you encounter the same issue.

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