feat: loop scroll

[Limbou]

Summary

Adds a loop parameter to ExpandablePageView and ExpandablePageView.builder that enables infinite scrolling by cycling through pages. Closes #50.
Changes

• New loop parameter (default: false) - When enabled, users can scroll infinitely in both directions, wrapping from the last page to the first and vice versa
• Virtual index approach - Uses a large virtual item count internally while exposing real indices (0 to itemCount-1) to the consumer
• Runtime loop toggling - Supports changing loop property dynamically while preserving the current page
• Validation - Assertions prevent loop: true with empty children

Usage

ExpandablePageView(
  loop: true,
  children: [Page1(), Page2(), Page3()],
)
ExpandablePageView.builder(
  loop: true,
  itemCount: 3,
  itemBuilder: (context, index) => pages[index],
)

[Copilot]

Pull request overview

This PR adds infinite loop scrolling functionality to the ExpandablePageView widget, allowing users to cycle through pages infinitely in both directions. This addresses issue #50 and provides a commonly requested feature for carousel-like experiences where pages wrap around from the last page to the first.

Key Changes

• Added loop parameter to enable infinite page scrolling with automatic wrapping
• Implemented virtual page index system using a large multiplier offset to support bidirectional infinite scrolling
• Updated size calculation logic to handle wrapped pages when viewportFraction < 1.0

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
lib/src/expandable_page_view.dart	Core implementation of loop functionality with virtual-to-real index mapping, internal controller management in loop mode, and viewport fraction calculations for wrapped pages
test/expandable_page_view_test.dart	Comprehensive test suite with 58 new tests covering loop behavior, edge cases, controller changes, and integration scenarios
CHANGELOG.md	Documentation of new feature addition

Comments suppressed due to low confidence (1)

lib/src/expandable_page_view.dart:351

• Incorrect listener removal. At line 347, the code attempts to remove _updatePage listener from oldWidget.controller. However, in non-loop mode, the listener was added to _pageController (line 325 or 349), not to oldWidget.controller.

If oldWidget.controller was provided, then _pageController == oldWidget.controller, so this works. But if oldWidget.controller was null, then _pageController was an internally created controller, and oldWidget.controller?.removeListener(_updatePage) does nothing (null-safe call). Then the old _pageController still has the listener attached when it's replaced by the new controller at line 348.

This creates a memory leak and potential crashes because:

1. The old internal controller (if it existed) is not properly cleaned up
2. The _updatePage callback will continue to be called on the old controller
3. The old controller is never disposed if _shouldDisposePageController was true

Fix:

if (oldWidget.controller != widget.controller && !widget.loop) {
  _pageController.removeListener(_updatePage);  // Remove from current controller
  if (_shouldDisposePageController) {
    _pageController.dispose();  // Dispose the old internal controller
  }
  _pageController = widget.controller ?? PageController();
  _pageController.addListener(_updatePage);
  _shouldDisposePageController = widget.controller == null;
}

    if (oldWidget.controller != widget.controller && !widget.loop) {
      // Only handle controller changes in non-loop mode
      // In loop mode, we manage our own internal controller
      oldWidget.controller?.removeListener(_updatePage);
      _pageController = widget.controller ?? PageController();
      _pageController.addListener(_updatePage);
      _shouldDisposePageController = widget.controller == null;
    }

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

lib/src/expandable_page_view.dart:351

• Memory leak: The old _pageController is not disposed when transitioning from an internal controller to an external controller in non-loop mode. When oldWidget.controller is null but widget.controller is provided, the old internal _pageController should be disposed before being replaced.

Consider adding:

if (oldWidget.controller != widget.controller && !widget.loop) {
  oldWidget.controller?.removeListener(_updatePage);
  if (oldWidget.controller == null && _shouldDisposePageController) {
    _pageController.dispose();
  }
  _pageController = widget.controller ?? PageController();
  _pageController.addListener(_updatePage);
  _shouldDisposePageController = widget.controller == null;
}

    if (oldWidget.controller != widget.controller && !widget.loop) {
      // Only handle controller changes in non-loop mode
      // In loop mode, we manage our own internal controller
      oldWidget.controller?.removeListener(_updatePage);
      _pageController = widget.controller ?? PageController();
      _pageController.addListener(_updatePage);
      _shouldDisposePageController = widget.controller == null;

---

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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