Stop the Bloat: Is Your Preview Code Outgrowing Your UI Components?

 Is your preview code bigger than your UI? Learn how PreviewParameterProvider keeps Jetpack Compose previews clean and maintainable.

Stop the Bloat: Is Your Preview Code Outgrowing Your UI Components?

This article is for Android developers using Jetpack Compose who feel their preview files are getting harder to maintain than the UI itself.

We’ve all been there. You finish a sleek, 20-line UI component, only to realize you’ve written 80 lines of Preview code to cover light mode, dark mode, font scaling, and various UI states.

If your preview logic is outweighing your actual features, you are doing it wrong. On large-scale design systems, this anti-pattern turns a simple UI tweak into a multi-file refactor.

Common Compose Preview Anti-Patterns

Before we fix it, let’s identify the “bloat” symptoms:

  • One preview per state: Creating separate functions like UserCardError() and UserCardLoading().
  • Copy-pasted theme wrappers: Wrapping every single preview in the same MyAppTheme { ... } block manually.

The Solution: PreviewParameterProvider

Instead of hardcoding every state, use a Provider to “inject” data into a single preview function. Think of it as a state factory.

1. Define Your UI State

data class ProfileUiState(
    val name: String,
    val bio: String,
    val isLoading: Boolean = false
)

2. Create the Parameter Provider

This class tells Compose exactly which variations you want to test.

import androidx.compose.ui.tooling.preview.PreviewParameterProvider

class ProfileStateProvider : PreviewParameterProvider<ProfileUiState> {
    override val values = sequenceOf(
        ProfileUiState(name = "Alex Smith", bio = "Android Dev"),
        ProfileUiState(name = "", bio = "", isLoading = true),
        ProfileUiState(name = "Error User", bio = "Failed to load")
    )

    // Fix the "data 0, data 1" naming problem in newer toolchain versions
    override fun getDisplayName(index: Int): String = when (index) {
        0 -> "Success State"
        1 -> "Loading State"
        2 -> "Error State"
        else -> super.getDisplayName(index)
    }
}

3. The Power Combo: Multi-Preview + Parameters

By combining a provider with Multi-preview annotations (like Material 3’s @PreviewLightDark), you multiply your coverage exponentially with one function.

@PreviewLightDark
@Composable
fun PreviewProfileCard(
    @PreviewParameter(ProfileStateProvider::class) state: ProfileUiState
) {
    // Generates 6 previews automatically: (3 states) x (2 themes)
    MyTheme {
        ProfileCard(state = state)
    }
}

Why This Wins

  • DRY (Don’t Repeat Yourself): Define the theme wrapper and layout logic exactly once.
  • Scalability: Need to test a 2.0x font size? Add one annotation, and all your states update.
  • Maintenance: If your component signature changes, you fix the call in one place.

🙋‍♂️ Frequently Asked Questions (FAQs)

Does using PreviewParameterProvider slow down the IDE?

Not significantly. While rendering 20 previews uses more RAM than one, managing them via a provider is more efficient for the IDE’s internal indexing than managing dozens of separate top-level functions.

Can I use multiple providers in one function?

Currently, Compose only supports one @PreviewParameter per function. To test combinations (e.g., UserType + ScreenOrientation), create a "Wrapper" data class that holds both.

Final Takeaway

Rule of thumb: If adding a new UI state requires creating a brand-new preview function, your previews are no longer scalable.

💬 Over to You!

  • How many preview functions are currently cluttering your largest UI file?
  • Have you tried creating Custom Multi-Preview Annotations for your brand’s specific device types?

📘 Master Your Next Technical Interview

Since Java is the foundation of Android development, mastering DSA is essential. I highly recommend “Mastering Data Structures & Algorithms in Java”. It’s a focused roadmap covering 100+ coding challenges to help you ace your technical rounds.

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