Update TickerMode.getValuesNotifier to handle initialization during State.dispose#185248
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This pull request updates TickerMode.getValuesNotifier to return a fallback value when the context is unmounted, preventing assertion errors that occur when late final animation controllers are disposed. It also adds regression tests for SingleTickerProviderStateMixin and TickerProviderStateMixin. The review feedback suggests removing the kDebugMode check to simplify the logic and ensure consistent behavior across all build modes.
| // The getInheritedWidgetOfExactType() method throws an assertion error if called during | ||
| // State.dispose(), which becomes a problem when an animation controller is set as a | ||
| // late final class member and isn't referenced until then. | ||
| if (kDebugMode && !context.mounted) { |
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The kDebugMode check is not strictly necessary here. If context.mounted is false, the element is defunct and getInheritedWidgetOfExactType would return null in release mode anyway (after a more expensive lookup). Removing kDebugMode simplifies the logic and provides a consistent, slightly more efficient path in all modes when the context is unmounted. This also aligns with the general practice of using context.mounted to guard against using a defunct context.
if (!context.mounted) {References
- Optimize for readability and avoid unnecessary complexity. (link)
| const fallback = _ConstantTickerModeDataListenable(TickerModeData.fallback); | ||
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| // The getInheritedWidgetOfExactType() method throws an assertion error if called during | ||
| // State.dispose(), which becomes a problem when an animation controller is set as a |
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This is technically not tied to animation controller, but the consumer of the VSync? (the class that mixes in the ticker provider)
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When getValuesNotifier is called during State.dispose, I guess you could say the call is tied to both the animation controller and the State subclass that mixes in the ticker provider.
When the animation controller object is being referenced for the first time, the AnimationController constructor is called, which then calls the ticker provider's createTicker method, and inside that method is where TickerMode.getValuesNotifier is eventually called.
Please let me know if I misunderstood your question!
victorsanni
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I would normally think we should throw the error anyways. But the fact that getValuesNotifier already has a fallback mechanism makes me think this PR is 👍
| // The getInheritedWidgetOfExactType() method throws an assertion error if called during | ||
| // State.dispose(), which becomes a problem when an animation controller is set as a | ||
| // late final class member and isn't referenced until then. | ||
| if (!context.mounted) { |
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context.getInheritedWidgetOfExactType throws if the current lifecycle state is not _ElementLifecycle.active. Is this == context.mounted?
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That's a good question!
If we land this change, hypothetically TickerMode.getValuesNotifier could still throw an error if a late animation controller is referenced for the first time while an element is in the middle of GlobalKey re-parenting.
But realistically, I don't think this a cause for concern.
justinmc
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LGTM 👍 . Is this the only thing blocking #153644? I think I missed that issue when you first created it, but reading through it now, I'm cautiously excited about it. It really simplifies things in the examples you gave at least.
I think so! I believe we can do a really nice cleanup once this PR lands. late final controller = AnimationController(vsync: this)..forward();The |
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Currently, TickerMode.getValuesNotifier assumes that
getInheritedWidgetOfExactTypeis safe to call, but there's an edge case where a widget defines an animation controller field and then is disposed of before that field is referenced elsewhere.This PR updates the logic in
getValuesNotifier()to handle that situation instead of throwing an error.related to #153644