fixed: reorder layer bug

[tushar11kh]

Fixes: #255 - Reorder Layer functionality fails with null check error when dragging items downward

Added index adjustment logic in the onReorder callback

Screen Record:

Screen.Recording.2025-10-08.at.1.03.59.PM.mov

Summary by Sourcery

Bug Fixes:

• Adjust newIndex when reordering items downward to avoid off-by-one null-check errors

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR patches an off-by-one issue in the layer reordering flow by inserting index adjustment logic into the onReorder callback, preventing null check errors when dragging items downward.

Sequence diagram for updated layer reordering logic

sequenceDiagram
actor User
participant "ReorderLayerSheet"
participant "onReorder callback"
User->>"ReorderLayerSheet": Drag layer from oldIndex to newIndex
"ReorderLayerSheet"->>"onReorder callback": Check if oldIndex == 0 or newIndex == 0
alt oldIndex < newIndex
    "ReorderLayerSheet"->>"onReorder callback": newIndex -= 1
end
"ReorderLayerSheet"->>"onReorder callback": Call onReorder(oldIndex, newIndex)

Loading

File-Level Changes

Change	Details	Files
Adjust newIndex to account for removal shift on downward drags	Insert conditional to decrement newIndex when oldIndex < newIndex before calling onReorder	lib/pro_image_editor/features/reorder_layer_example.dart

Possibly linked issues

• Bug: Reorder Layer #255: The PR fixes the reorder layer bug by adding index adjustment logic when dragging items downward.
• Bug: Reorder Layer #255: The PR fixes the layer reordering bug by adding index adjustment logic in the onReorder callback.

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[sourcery-ai]

Hey there - I've reviewed your changes - here's some feedback:

• Consider adding explicit bounds checking for newIndex (e.g., clamping it to the list length) to avoid potential out-of-range errors when dragging items to the very end.
• The early return for index 0 is a bit implicit—extract the magic number into a named constant or add a comment explaining why reordering at index 0 is disallowed to improve readability.
• To make the adjustment logic clearer, factor the if (oldIndex < newIndex) newIndex -= 1 into a small helper or annotate it to explain that it compensates for the removed item's shift.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider adding explicit bounds checking for newIndex (e.g., clamping it to the list length) to avoid potential out-of-range errors when dragging items to the very end.
- The early return for index 0 is a bit implicit—extract the magic number into a named constant or add a comment explaining why reordering at index 0 is disallowed to improve readability.
- To make the adjustment logic clearer, factor the `if (oldIndex < newIndex) newIndex -= 1` into a small helper or annotate it to explain that it compensates for the removed item's shift.

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[tushar11kh]

@mariobehling can you review and merge this pr?

[tushar11kh]

@hpdang can review and merge it please?