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Update guidance around dart:ffi in widget previews #89

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johnpryan merged 1 commit into from
Apr 24, 2026
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Update guidance around dart:ffi in widget previews #89

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2 changes: 1 addition & 1 deletion skills/flutter-add-widget-preview/SKILL.md
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Expand Up @@ -27,7 +27,7 @@ Use the Flutter Widget Previewer to render widgets in real-time, isolated from t

Adhere to the following constraints when authoring previewable widgets, as the Widget Previewer runs in a web environment:

- **No Native APIs:** Do not use native plugins or APIs from `dart:io` or `dart:ffi`. Widgets with transitive dependencies on `dart:io` will throw exceptions upon invocation, and `dart:ffi` dependencies will fail to load. Use conditional imports to mock or bypass these in preview mode.
- **No Native APIs:** Do not use native plugins or APIs from `dart:io` or `dart:ffi`. Widgets with transitive dependencies on `dart:io` or `dart:ffi` will throw exceptions upon invocation. Use conditional imports to mock or bypass these in preview mode.
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@gemini-code-assist gemini-code-assist Bot Apr 24, 2026

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medium

The updated wording suggests that any widget with a transitive dependency on dart:io or dart:ffi will throw an exception upon invocation. It is clearer to specify that the exception occurs when the APIs are invoked. Additionally, since the primary change (resolved in Flutter 3.41) is that these dependencies no longer prevent compilation, explicitly mentioning this improvement provides valuable context for developers who may have previously avoided these libraries.

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- **No Native APIs:** Do not use native plugins or APIs from `dart:io` or `dart:ffi`. Widgets with transitive dependencies on `dart:io` or `dart:ffi` will throw exceptions upon invocation. Use conditional imports to mock or bypass these in preview mode.
- **No Native APIs:** Do not use native plugins or APIs from `dart:io` or `dart:ffi`. While transitive dependencies on these libraries no longer prevent compilation, invoking their APIs will throw exceptions in the previewer. Use conditional imports to mock or bypass these in preview mode.

- **Asset Paths:** Use package-based paths for assets loaded via `dart:ui` `fromAsset` APIs (e.g., `packages/my_package_name/assets/my_image.png` instead of `assets/my_image.png`).
- **Public Callbacks:** Ensure all callback arguments provided to preview annotations are public and constant to satisfy code generation requirements.
- **Constraints:** Apply explicit constraints using the `size` parameter in the `@Preview` annotation if your widget is unconstrained, as the previewer defaults to constraining them to approximately half the viewport.
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