Introduction

This blog post provides a summary of how to utilize Jetpack Compose previews for testing your UI across various devices and configurations.

Benefits of using previews

  • Test UI on different devices and configurations: Previews allow you to see how your UI looks on various screen sizes, font scales, and device orientations without running the app on each device.
  • Faster development: Previews provide a quicker way to test and iterate on your UI compared to manually deploying the app to different devices.
  • Improved UI quality: By testing on various configurations, you can ensure your UI looks good and functions properly across a wider range of devices.

How to use previews

  1. Add the androidx.compose.ui:ui-tooling dependency: This dependency provides the necessary classes for creating previews.
  2. Use the @Preview annotation: Annotate your composable functions with @Preview to mark them as previews.
  3. Customize previews: You can customize previews with various options:
    • name: Provide a name to easily identify different previews.
    • width and height: Specify custom dimensions for the preview.
    • device: Choose a specific device to preview on (e.g., Pixel 3A).
    • fScale: Set the font scale to test different font sizes.
    • locale: Preview the UI with different locales/languages.
    • showSystemUi: Show the status bar and navigation bar in the preview.
    • backgroundColor: Set a custom background color for the preview.
  4. Live edits: With newer Android Studio versions, you can directly edit colors and other properties in the preview and see the changes reflected immediately.
  5. Run previews on real devices: You can run previews directly on your connected devices to see how they look on real hardware.
  6. Interactive mode: Interact with clickable elements in the preview to test their functionality.
  7. Animation preview: Preview and step through animations frame by frame.
  8. Multiple previews: Create multiple previews with different configurations to test various scenarios.
  9. Parameter providers: Pass data to previews to test different UI states and data sets.

Limitations of previews

  • Network data: Previews do not show network data. You need to provide mock data manually.
  • Large data sets: For large data sets, use parameter providers or statically add data.
  • Dependency injection: You cannot directly pass view models to previews due to limitations with local composition scope.
  • Boilerplate code: Setting up previews can involve some boilerplate code.

Conclusion

Jetpack Compose previews are a powerful tool for testing and improving your UI. By using previews effectively, you can save time, improve UI quality, and ensure your app looks good on a wide range of devices.