Check listener state before set new value

[robzimpulse]

Description

Check ValueNotifier disposed state before set new value. Sometimes, the cancellation callback is triggered after closing the screen (pager were disposed) hence triggering exception.

Type of Change

• [❌ ] ✨ New feature (non-breaking change which adds functionality)
• [✅] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [❌] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [✅] 🧹 Code refactor
• [❌] ✅ Build configuration change
• [❌] 📝 Documentation
• [❌] 🗑️ Chore

Summary by CodeRabbit

• Refactor
  • Optimized state management efficiency to reduce unnecessary updates and improve application performance.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

The PageFetcher class adds a setter override for the value property that guards state updates with a hasListeners check. Updates are prevented when no listeners are present; otherwise, the update delegates to the parent class.

Changes

Cohort / File(s)	Summary
ValueNotifier Setter Guard lib/src/page_fetcher.dart	Added value setter override in PageFetcher<Key, Value> that early-returns if hasListeners is false, preventing unnecessary state propagation when no listeners exist.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐰 A hop, a check, a guard so keen,
No listeners? The value stays serene,
We skip the update, save the day,
In Notifier land, efficiency's the way!
✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately describes the main change: adding a listener state check before updating the value in the ValueNotifier.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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