expansion_tile_list 2.0.0

A customizable set of expansion tiles with versatile options for styling, animations, and control over expansion behavior, while streamlining essential features for ease of use.

Expansion Tile List

The ExpansionTileList serves as a container for the ExpansionTile widget, enabling the creation of a list of ExpansionTile items. It offers additional features that allow you to customize the appearance of the tiles and control their expansion programmatically.

Table of Contents

• Description
• Features
  • List Features
  • Item Features
• Installation
• Usage
  • Basic
  • Separator And Gap
  • Controller
  • ExpansionMode
  • ExpansionTileItem
  • Reorderable
  • Drag Handle
• How Drag Handle works
• How initialExpandedIndexes with ExpansionMode works
• How itemGapSize and separatorBuilder layout works
• How ExpansionTileList current position and initial position works
  • Method: initialPosition
  • Method: currentPosition
• List Properties
• Scrollable Properties
• Reorderable Properties
• Item Properties
• Testing
• Troubleshooting
• Known Issues & Fixes
• Contributing

Description

The expansion_tile_list package offers a highly customizable list of expansion_tile items for Flutter applications. It enables developers to create expandable tile lists with extensive options for appearance, animations, and control over the expansion behaviour. The package includes features such as a global trailing widget, trailing animation, and various expansion modes to accommodate different use cases.

Features

• Compatible with ExpansionTile widgets.
• Includes additional features when using ExpansionTileItem widget instead of ExpansionTile
• Supports hot reload.🔥
• Accordion like expansion mode and many more.
• Customizable trailing widget and trailing animation.
• Customize the appearance of the tiles using itemBuilder, separatorBuilder and itemGapSize.
• Programmatically control the expansion of the tiles with ExpansionTileListController.
• Listen to the expansion changes of the tiles.
• Drag and reorder the items in the list.
• Checkout the Demo to explore the latest features and experience the features firsthand!

List Features

All the features affects all the tiles in the ExpansionTileList.

• itemGapSize allows you to specify the size of the gap between each tile in the ExpansionTileList.
• trailing allows you to specify the trailing widget for all tiles, can be overridden byExpansionTile trailing property.
• trailingAnimation allows you to specify a custom animation for the trailing widget.
• enableTrailingAnimation allows you to enable or disable the trailing animation.
• itemBuilder allows the customization of the creation and appearance of the tiles in the ExpansionTileList.
• separatorBuilder allows the customization of the creation and appearance of the separators between the tiles in the ExpansionTileList.
• initialExpandedIndexes allows you to specify the indexes of the tiles that are initially expanded.
• controller allows you to programmatically control the expansion of the tiles.
• onExpansionChanged allows you to listen to the expansion changes of the tiles.
• ExpansionMode allows you to specify the expansion mode for the ExpansionTileList.
  • ExpansionMode.atMostOne allows you to expand at most one tile at a time. (i.e. zero or one )
  • ExpansionMode.atLeastOne ensures that at least one tile is always expanded (i.e. one or more )
  • ExpansionMode.exactlyOne allows you to expand exactly one tile at a time. (i.e. one )
  • ExpansionMode.any allows you to expand any number of tiles. (i.e. zero or more )
• separatorAlignment allows you to specify the alignment of the separator against the space itemGapSize between the tiles in the ExpansionTileList
• ExpansionTileList.reorderable enable the list to be reorderable by dragging the items.
• Reorderable callbacks e.g canReorder onReorder allows you to specify a callback to control the behavior of the list item reordering.
• dragHandleBuilder allows you to customize the appearance of the drag handle for the reorderable list.

Item Features

By default ExpansionTileList supports ExpansionTile widget as children to create tiles. But you can also use ExpansionTileItem widget when more control is required. All the properties overrides the that of ExpansionTileList.

• trailing allows you to specify the trailing widget for the tile.
• trailingAnimation allows you to specify a custom animation for the trailing widget.
• enableTrailingAnimation allows you to enable or disable the trailing animation.

Installation

To use this package, add expansion_tile_list as a dependency in your pubspec.yaml file.

dependencies:
  flutter:
    sdk: flutter
  expansion_tile_list: ^2.0.0

Usage

Import the package:

import 'package:expansion_tile_list/expansion_tile_list.dart';

Here are some simple examples of how to use the ExpansionTileList: check out the demo

Basic

• Simple usage: create a list of ExpansionTile widgets using the ExpansionTileList widget.

import 'package:flutter/material.dart';
import 'package:expansion_tile_list/expansion_tile_list.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: ExpansionTileList(
          itemGapSize: 10.0,
          children: <Widget>[
            ExpansionTile(
              title: Text('Tile 1'),
              children: <Widget>[
                Text('Child 1'),
              ],
            ),
            ExpansionTile(
              title: Text('Tile 2'),
              children: <Widget>[
                Text('Child 2'),
              ],
            ),
          ],
        ),
      ),
    );
  }
}

• Using trailing and trailingAnimation: use the trailing and trailingAnimation properties to customize the trailing widget of the tiles.

var expansionTileList =
ExpansionTileList(
  trailing: Icon(Icons.arrow_drop_down),
  trailingAnimation: ExpansionTileAnimation(
    tween: Tween<double>(begin: 0, end: 0.5),
    duration: Duration(milliseconds: 200),
    curve: Curves.easeInOut,
    builder: (context, index, value, child) {
      return Transform.rotate(
        angle: value * pi,
        child: child,
      );
    },
  ),
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using itemBuilder: This property allows you to customize the appearance of the items in the list.

var expansionTileList = ExpansionTileList(
  itemBuilder: (context, index, isExpanded, child) {
    return Container(
      color: isExpanded ? Colors.blue : Colors.white,
      child: child,
    );
  },
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using onExpansionChanged: This property allows you to listen to the expansion changes of the tiles.

var expansionTileList = ExpansionTileList(
  onExpansionChanged: (index, isExpanded) {
    print('Tile $index is ${isExpanded ? 'expanded' : 'collapsed'}');
  },
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

Separator And Gap

**See Also: ** How itemGapSize and separatorBuilder layout works

• Using itemGapSize: This property allows you to specify the size of the gap between each tile in the list.

var expansionTileList = ExpansionTileList(
  itemGapSize: 10.0, // defaults to 0.0 if not specified
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using separatorBuilder: This property allows you to customize the appearance of the separators between the ExpansionTile items in the list.

var expansionTileList =
ExpansionTileList(
  separatorAlignment: Alignment.topCenter, // defaults to Alignment.bottomCenter if not specified
  separatorBuilder: (context, index, value, child) {
    return Divider(
      color: Colors.blue,
      height: 2.0,
    );
  },
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using separatorAlignment: This property allows you to specify the alignment of the separator against the space itemGapSize between the tiles in the list.

var expansionTileList = ExpansionTileList(
  separatorAlignment: Alignment.topCenter, // defaults to Alignment.bottomCenter if not specified
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

Controller

**See Also: ** How ExpansionTileList current position and initial position works

• Using controller: This property allows you to programmatically control the expansion of the ExpansionTile items.

var controller = ExpansionTileListController();

var expansionTileList = ExpansionTileList(
  controller: controller,
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

_() {
  /// Expand the first tile
  controller.expand(0);

  /// Collapse the first  tile
  controller.collapse(0);

  /// Toggle the first 
  controller.toggle(0);

  /// Expand all 
  controller.expandAll();

  /// Collapse all tiles
  controller.collapseAll();

  ///
  controller.toggleAll();

  ///
  controller.initialPosition(currentPosition);

  ///
  controller.currentPosition(initialPosition);
}

ExpansionMode

**See Also: ** How initialExpandedIndexes with ExpansionMode works

• Using ExpansionMode: Use ExpansionMode property of the ExpansionTileList widget to control the expansion of the tiles. The initialExpandedIndexes property allows you to specify the indexes of the tiles that are initially expanded. ExpansionMode that enforces a single tile expansions at a time expects a single index in the array initialExpandedIndexes i.e. ExpansionMode.atMostOne and ExpansionMode.exactlyOne, if multiple indexes are specified then only the first index at 0 is considered. If the initialExpandedIndexes is not specified then the first tile is expanded by default.

/// Use ExpansionMode property
/// length of `initialExpandedIndexes` for enforces at least one tile always expanded [`ExpansionMode.atLeastOne`, `ExpansionMode.exactlyOne`] should be 1 or 0.
var expansionTileList = ExpansionTileList(
  initialExpandedIndexes: [0, 1], // defaults to [] if not specified
  expansionMode: ExpansionMode.any, // defaults to ExpansionMode.any if not specified
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

// Use named constructor
var expansionTileList = ExpansionTileList(
  expansionMode: ExpansionMode.atMostOne,
  initialExpandedIndexes: [0], // defaults to [] if not specified
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

var expansionTileList = ExpansionTileList(
  expansionMode: ExpansionMode.atLeastOne,
  initialExpandedIndexes: [1],
  // defaults to [0] if not specified and cannot be resolved by first initialExpandedIndex of children
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

var expansionTileList = ExpansionTileList(
  expansionMode: ExpansionMode.exactlyOne,
  initialExpandedIndexes: [0], // defaults to [0] if not specified
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

ExpansionTileItem

ExpansionTileItem is an alternative to the default ExpansionTile, it intend to provide more fine grained control over the default where necessary.

• Using ExpansionTileItem: Use the ExpansionTileItem widget to customize the trailing widget of the tiles.

var expansionTileList = ExpansionTileList(
  children: <ExpansionTile>[
    ExpansionTileItem(
      title: Text('Tile 1'),
      trailing: Icon(Icons.arrow_drop_down),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTileItem(
      title: Text('Tile 2'),
      trailing: Icon(Icons.arrow_drop_down),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using ExpansionTileItem with trailingAnimation: Use the ExpansionTileItem widget with the trailingAnimation property to customize the trailing widget of the tiles.

var expansionTileList = ExpansionTileList(
  children: <ExpansionTile>[
    ExpansionTileItem(
      title: Text('Tile 1'),
      trailing: Icon(Icons.arrow_drop_down),
      trailingAnimation: Tween<double>(begin: 0, end: 0.5),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTileItem(
      title: Text('Tile 2'),
      trailing: Icon(Icons.arrow_drop_down),
      trailingAnimation: Tween<double>(begin: 0, end: 0.5),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using ExpansionTileItem with trailingAnimationBuilder: Use the ExpansionTileItem widget with the trailingAnimationBuilder property to customize the trailing widget of the tiles.

var expansionTileList = ExpansionTileList(
  children: <ExpansionTile>[
    ExpansionTileItem(
      title: Text('Tile 1'),
      trailing: Icon(Icons.arrow_drop_down),
      trailingAnimationBuilder: (context, index, value, child) {
        return Transform.rotate(
          angle: value * pi,
          child: child,
        );
      },
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTileItem(
      title: Text('Tile 2'),
      trailing: Icon(Icons.arrow_drop_down),
      trailingAnimationBuilder: (context, index, value, child) {
        return Transform.rotate(
          angle: value * pi,
          child: child,
        );
      },
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

Reorderable

• Using ExapnsionTileList.reorderable: Use the ExpansionTileList.reorderable constructor to enable the list to be reorderable by dragging the items.

var expansionTileList = ExpansionTileList.reorderable(
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using callbacks with reorderable : Use the callbacks to listen to the reordering of the items in the list.

// Use the canReorder and onReorder callback
var expansionTileList = ExpansionTileList.reorderable(
  canReorder: (oldIndex, newIndex) { // allow reordering only if the new index is greater than the old index (drag down)
    return newIndex > oldIndex;
  },
  onReorder: (oldIndex, newIndex) {
    print('Reordered from $oldIndex to $newIndex');
  },
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

// Use the onReorderStart and onReorderEnd callback
var expansionTileList = ExpansionTileList.reorderable(
  onReorderStart: (index) { // called when the reordering starts at the index
    print('Reorder started at $index');
  },
  onReorderEnd: (index) { // called when the reordering ends at the index
    print('Reorder ended at $index');
  },
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using useDelayedDrag: Use the useDelayedDrag property to enable delayed drag (long press) to start reordering the items in the list.

var expansionTileList = ExpansionTileList.reorderable(
  useDelayedDrag: true, // enable delayed drag (long press) to start reordering
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using proxyDecorator: Use the proxyDecorator property to customize the appearance of the proxy item that is displayed while reordering the items in the list.

var expansionTileList = ExpansionTileList.reorderable(
  proxyDecorator: (Widget child, int index,
      Animation<double> animation) { // customize the appearance of the proxy item during reordering (dragging)
    return Material(
      elevation: 4.0,
      child: SizeTransition(
        sizeFactor: animation,
        child: child,
      ),
    );
  },
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ]
  ,
);

Drag Handle

NOTE: The drag handle is a widget used to reorder the items in the list by dragging.

• Using enableDefaultDragHandles : Use the enableDefaultDragHandles property to enable the default drag handles for the reorderable list and useDelayedDrag for a long press to trigger reordering. The default drag handles makes the whole ExpansionTile item draggable. This can be set to false when a custom drag handle is required.

// Use default drag handles with delayed drag
var expansionTileList = ExpansionTileList.reorderable(
  enableDefaultDragHandles: true, // defaults to true if not specified
  useDelayedDrag: true, // enable delayed drag (long press) to start reordering
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using DragHandlePlacement: Use the dragHandlePlacement property to specify the placement of the drag handle for the reorderable list.

var expansionTileList = ExpansionTileList.reorderable(
  dragHandlePlacement: DragHandlePlacement.trailing, // defaults to DragHandlePlacement.none if not specified
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using dragHandleAlignment: Use the dragHandleAlignment property to specify the horizontal alignment of the drag handle relative to its placement for the reorderable list.

var expansionTileList = ExpansionTileList.reorderable(
  dragHandleAlignment: HorizontalAlignment.centerRight, // defaults to HorizontalAlignment.centerLeft if not specified
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using dragHandleBuilder: Use the dragHandleBuilder property to customize the appearance of the drag handle for the reorderable list based on the DragHandlePlacement value. NOTE: DragHandlePlacement.none does not call the dragHandleBuilder. The dragHandleBuilder can be used as a custom drag handle when the enableDefaultDragHandles is set to false.

// decorate the drag handle based on DragHandlePlacement (child is the drag handle placement widget (leading , trailing or title))
// DragHandlePlacement.none does not call the dragHandleBuilder
var expansionTileList = ExpansionTileList.reorderable(
  dragHandlerPlacement: DragHandlePlacement.leading,
  // important for dragHandleBuilder to know the placement of the drag handle
  dragHandleBuilder: (context, index, child) { // customize the appearance of the drag handle
    return child == null ? const Icon(Icons.drag_handle) : Row(
      mainAxisSize: MainAxisSize.min, //give it a min size to avoid overflow
      children: <Widget>[
        const Icon(Icons.drag_handle),
        !child,
      ],
    );
  },
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

// use as a custom drag handle (only a specific widget is used as the handle)
// disable the default drag handles (enableDefaultDragHandles = false) and use either the ReorderableDragStartListener or ReorderableDelayedDragStartListener to create a custom drag handle for the reorderable list.
var expansionTileList = ExpansionTileList.reorderable(
  enableDefaultDragHandles: false,
  // disable the default drag handles
  dragHandlerPlacement: DragHandlePlacement.leading,
  // important for dragHandleBuilder to know the placement of the drag handle
  dragHandleBuilder: (context, index, child) { // customize the appearance of the drag handle
    final dragHandle = ReorderableDragStartListener(
      key: PageStorageKey(index),
      index: index,
      child: const Icon(Icons.drag_handle),
    );
    return child == null ? dragHandle : Row(
      mainAxisSize: MainAxisSize.min, //give it a min size to avoid overflow
      children: <Widget>[
        dragHandle,
        !child,
      ],
    );
  },
  children: <ExpansionTile>[
    ExpansionTile(
      title: Text('Tile 1'),
      children: <Widget>[Text('Child 1')],
    ),
    ExpansionTile(
      title: Text('Tile 2'),
      children: <Widget>[Text('Child 2')],
    ),
  ],
);

• Using Custom Drag Handle: Disable the default drag handles and use either the ReorderableDragStartListener or ReorderableDelayedDragStartListener to create a custom drag handle for the reorderable list.
  1. create a custom drag handle (e.g Icon)
  2. set enableDefaultDragHandles to false
  3. create an ExpansionTileController to programmatically control the tiles and access the position of the tiles
  4. wrap the drag handle with ReorderableDragStartListener or ReorderableDelayedDragStartListener
  5. wrap the ReorderableDragStartListener or ReorderableDelayedDragStartListener with a ValueListenableBuilder to update the index property of the drag handle
  6. update the index property of the drag handle ReorderableDragStartListener or ReorderableDelayedDragStartListener to the current position of th ExpansionTile every time the list is reordered by using the onReorder callback.

NOTE: dragHandleBuilder is a simpler way to create a custom drag handle for the reorderable list.

final ValueNotifier<(int, int)> _reorderNotifier = ValueNotifier((-1, -1)); // remember to dispose the ValueNotifier
final ExpansionTileListController _controller = ExpansionTileListController();

var expansionTileList = ExpansionTileList.reorderable(
  enableDefaultDragHandles: false, // defaults to true if not specified
  controller: _controller, // controller to programmatically control tiles and access the position of the tiles
  onReorder: (oldIndex, newIndex) {
    _reorderNotifier.value = (oldIndex, newIndex); // notify the custom drag handle of the reorder
  },
  children: <ExpansionTile>[
    ...List.generate(10, (index) {
      return ExpansionTile(
        leading: _buildCustomDragHandle(index),
        title: Text('Tile $index'),
        children: <Widget>[Text('Child $index')],
      );
    }),
  ],
);

Widget _buildCustomDragHandle(int itemIndex) {
  return ValueListenableBuilder<(int, int)>(
      valueListenable: _reorderNotifier,
      builder: (context, (int, int) value, child) {
        return ReorderableDragStartListener(
          key: PageStorageKey(itemIndex),
          index: _controller.currentPosition(itemIndex),
          child: const Icon(Icons.drag_handle),
        );
      });
}

// for large items in a list, to improve performance a custom drag handle can be created as below
// Note: _reorderNotifier should be reset to (-1, -1) in the didUpdateWidget lifecycle method when setState is called to rebuild the list.
@Override
void didUpdateWidget() {
  _reorderNotifier.value = (-1, -1);
}

Widget _buildCustomDragHandle(int itemIndex) {
  Widget dragHandle(int index) {
    return ReorderableDragStartListener(
      key: PageStorageKey(index),
      index: index,
      child: const Icon(Icons.drag_handle),
    );
  }

  Widget? currentDragHandle;
  return ValueListenableBuilder<(int, int)>(
    valueListenable: _reorderNotifier,
    child: currentDragHandle,
    builder: (context, (int, int) value, child) {
      var minIndex = min(value.$1, value.$2);
      var maxIndex = max(value.$1, value.$2);
      var index = _controller.currentPosition(itemIndex);
      if (minIndex < 0 || (index >= minIndex &&
          index <= maxIndex)) { //only update when reorder index is within the range of oldIndex and newIndex or is -1
        currentDragHandle =
            (index == itemIndex ? child : null) ?? dragHandle(index);
      }
      return currentDragHandle ?? dragHandle(index);
    },
  );
}

How Drag Handle works

By default the whole widget is draggable for a reorderable expansion list. To create use a widget as a drag handle, use dragHandleBuilder to customize the appearance of the drag handle and use dragHandlePlacement and dragHandleAlignment to specify the placement and alignment of the drag handle respectively. For a custom drag handle, disable the default drag handles by setting enableDefaultDragHandles to false.

• enableDefaultDragHandles is used to enable the default drag handles for the reorderable list. Only set false if you intend to build custom drag handles.
• useDelayedDrag is used to enable the delayed drag (long press) to start reordering.
• dragHandlePlacement is used to specify the placement of the drag handle. This works for both the default drag handles and the custom drag handles (i.e enableDefaultDragHandles is false).
• dragHandleAlignment is used to specify the alignment of the drag handle in relation to the space between the tiles.
• dragHandleBuilder is used only when dragHandlePlacement has a value other than DragHandlePlacement.none to customize the appearance of the drag handle based on the DragHandlePlacement widget.

How initialExpandedIndexes with ExpansionMode works

• ExpansionMode.atMostOne
  • considers initialExpandedIndexes first valid index.
  • considers first ExpansionTile child widget withinitiallyExpanded true.
  • collapses all tiles.
• ExpansionMode.exactlyOne
  • considers initialExpandedIndexes first valid index.
  • considers first ExpansionTile child widget withinitiallyExpanded true.
  • considers first ExpansionTile child widget at index 0.
• ExpansionMode.atLeastOne
  • considers initialExpandedIndexes all indexes if not empty.
  • considers all ExpansionTile children widget withinitiallyExpanded true.
  • considers first ExpansionTile child widget at index 0.
• ExpansionMode.any
  • considers initialExpandedIndexes all indexes if not empty.
  • considers all ExpansionTile children widget withinitiallyExpanded true.
  • collapses all tiles.

How itemGapSize and separatorBuilder layout works

• itemGapSize is the size of the gap between the tiles in the list.
• separatorBuilder is the builder which returns a separator widget rendered between the ExpansionTile items in the list.
• separatorAlignment is the alignment of the separator widget in relation to the space itemGapSize between items.

NOTE: The separatorAlignment can be used to specify the alignment of the separator against the space

Layout as follows:

Alignment.topLeft           Alignment.topCenter         Alignment.topRight

[ExpansionTile 1]           [ExpansionTile 1]           [ExpansionTile 1]  
[     Gap       ]           [     Gap       ]           [      Gap      ]  
[Divider]                       [Divider]                       [Divider]

[ExpansionTile 2]           [ExpansionTile 2]           [ExpansionTile 2]  
[     Gap       ]           [     Gap       ]           [      Gap      ]  
[Divider]                       [Divider]                       [Divider]

[ExpansionTile 3]           [ExpansionTile 3]           [ExpansionTile 3]  

Alignment.centerLeft        Alignment.center            Alignment.centerRight

[ExpansionTile 1]           [ExpansionTile 1]           [ExpansionTile 1]  
[     Gap/2     ]           [     Gap/2     ]           [     Gap/2     ]  
[Divider]                   [Divider]                   [Divider]  
[     Gap/2     ]           [     Gap/2     ]           [     Gap/2     ]  

[ExpansionTile 2]           [ExpansionTile 2]           [ExpansionTile 2]  
[     Gap/2     ]           [     Gap/2     ]           [     Gap/2     ]  
[Divider]                   [Divider]                   [Divider]  
[     Gap/2     ]           [     Gap/2     ]           [     Gap/2     ]  

[ExpansionTile 3]           [ExpansionTile 3]           [ExpansionTile 3]  

Alignment.bottomLeft        Alignment.bottomCenter      Alignment.bottonRight

[ExpansionTile 1]           [ExpansionTile 1]           [ExpansionTile 1]  
[Divider]                   [Divider]                   [Divider]  
[     Gap       ]           [     Gap       ]           [      Gap      ]

[ExpansionTile 2]           [ExpansionTile 2]           [ExpansionTile 2]  
[Divider]                   [Divider]                   [Divider]  
[     Gap       ]           [     Gap       ]           [      Gap      ]  

[ExpansionTile 3]           [ExpansionTile 3]           [ExpansionTile 3]  

How ExpansionTileList current position and initial position works

• The ExpansionTileList item initial position is the index of the ExpansionTile in the children list of the ExpansionTileList on creation and before reordering.
• For a non-reorderable ExpansionTileList, an item current position will always be the same as the initial position.
• For a reorderable ExpansionTileList, the current position is the index of the ExpansionTile in the items of the ExpansionTileList after reordering.
• Before reordering, the current position is the same as the initial position.
• After reordering, the current position is updated to the new index of the ExpansionTile in the items of the ExpansionTileList.
• Both the initial position and current position are zero-based indexes.
• All ExpansionTileList callbacks and methods that require a position or index use the current position.

Method : initialPosition

• Returns the initial position(index) of the tile at the given current position(index).
• The initial position is the original position of the tile in the list.
• For example, A tile at the initial index 0 will be assigned a position 0,
• if the tile is moved to the position 2, the initial position of the tile at the position 2 will still be 0.
• Therefore, initial position is the position of the tile in the list before any reordering and it remains the same after reordering.

var controller = ExpansionTileListController();

_() {
// before reordering
  controller.initialPosition(0); // returns 0
// after reordering
  controller.initialPosition(2); // returns 0
}

Method : currentPosition

• Returns the current position(index) of the tile at the given initial position(index).
• The current position is the updated position of the tile in the list after reordering.
• For example, A tile at the initial index 0 will be assigned a position 0,
• if the tile is moved to the position 2, the current position of the tile at the position 0 will be 2.
• Therefore, current position is the position of the tile in the list after reordering.

var controller = ExpansionTileListController();

_() {
// before reordering
  controller.currentPosition(0); // returns 0
// after reordering
  controller.currentPosition(0); // returns 2
}

List Properties

Property	Description	Default Value
key	The widget key.	null
children	The list of ExpansionTile widgets that are managed by this widget.	required
onExpansionChanged	Called whenever a tile is expanded or collapsed.	null
itemGapSize	The size of the gap between the tiles in the list. (renamed to itemGapSize from next major release)	0.0
separatorBuilder	The builder for the separator between the tiles in the list.	null
itemBuilder	A builder that can be used to customize the appearance of the tiles. (renamed to itemBuilder from next major release)	null
controller	A controller that can be used to programmatically control the expansion of the tiles.	null
trailing	The widget that is displayed at the end of each tile header. Can be overridden by trailing property of ExpansionTile	null
trailingAnimation	The animation for the trailing widget of the tiles. Can be overridden by trailingAnimation property of ExpansionTile	null
enableTrailingAnimation	Enable or disable the trailing animation.	true
initialExpandedIndexes	The indexes of the tiles that are initially expanded.	const <int>[]
expansionMode	The expansion mode of the ExpansionTileList.	ExpansionMode.any
separatorAlignment	The alignment of the separator widget in relation to the space itemGapSize between items	Alignment.bottomCenter

Scrollable Properties

Property	Description	Default Value
scrollDirection	The direction in which the list scrolls	Axis.vertical
reverse	Whether the list scrolls in reverse	false
scrollController	An object that can be used to control the position to which this scroll view is scrolled.	null
primary	Whether this is the primary scroll view associated with the parent PrimaryScrollController.	true
physics	How the scroll view should respond to user input.	AlwaysScrollableScrollPhysics()
shrinkWrap	Whether the extent of the scroll view in the scroll direction should be determined by the contents being viewed.	false
padding	The amount of space by which to inset the list contents.	EdgeInsets.zero
restorationId	An identifier that will be used to save the scroll position in the restoration data.	null
keyboardDismissBehavior	How the scroll view should respond to keyboard events.	ScrollViewKeyboardDismissBehavior.manual
dragStartBehavior	Determines the way that drag start behavior is handled.	DragStartBehavior.start
clipBehavior	Determines how to clip the content of the scroll view.	Clip.hardEdge

Reorderable Properties

Property	Description	Default Value
reorderable	Readonly bool property indicating if the ExpansionTileList can be reordered	false
canReorder	A callback that returns whether the item at the given index can be reordered.	null
onReorder	A callback invoked when an item has been reordered.	null
onReorderStart	A callback invoked when the user starts reordering an item	null
onReorderEnd	A callback invoked when the user stops reordering an item	null
proxyDecorator	A builder that can be used to customize the appearance of the proxy item that is displayed while reordering.	null
enableDefaultDragHandles	A bool property indicating if the default drag handles should be used for the reorderable list.	true
useDelayedDrag	A bool property indicating if delayed (long press) drag start should trigger item reordering.	false
dragHandlePlacement	The placement of the drag handle in the ExpansionTile.	DragHandlePlacement.none
dragHandleAlignment	The alignment of the drag handle in the ExpansionTile.	HorizontalAlignment.centerLeft
dragHandleBuilder	A builder that can be used to customize the appearance of the drag handle for the reorderable list.	null
anchor	Determines the relative position of the zero scroll offset within the viewport. (values: 0.0 to 1.0)	0.0
autoScrollerVelocityScalar	Enables you to adjust the speed of the auto-scroll behavior during drag-and-drop operations	50

Item Properties

Property	Description	Default Value
controller	Programmatically control the expansion using ExpansionTileController or ExpansionTileItemController.	null
trailing	The widget that is displayed at the end of each tile header.	null
trailingAnimation	The animation for the trailing widget of the tiles.	null
enableTrailingAnimation	Enable or disable the trailing animation.	true

Testing

All testcase are available for the source.

• expansion_tile_list_test.dart
• expansion_tile_item_test.dart
• expansion_tile_extension_test.dart To run the tests, use the following command:

flutter test

Troubleshooting

1. If you encounter any issues while using the package, please check the GitHub issues page to see if the issue has already been reported.
2. If you are unable to find a solution, please create a new issue with a detailed description of the problem, including the steps to reproduce it.
3. If you have any questions or need help with the package, please feel free to reach out to the package maintainer.
4. If you would like to contribute to the package, please refer to the Contributing section for more information.
5. If you have any feedback or suggestions for the package, please share them with the package maintainer.

Known Issues & Fixes

• State Management issues with ExpansionTile children: Set maintainState to true for the ExpansionTile children to maintain the state of the children when the parent ExpansionTileList is rebuilt.
• Expansion state issues: The expansion state of the ExpansionTile may not be maintained when the parent of ExpansionTileList is rebuilt due to the change of the widget tree. To maintain the expansion state, use a GlobalKey on the ExpansionTile.
• ExpansionTileList itemBuilder issues: If the itemBuilder modifies the widget tree during a rebuild, it may disrupt the maintenance of the expansion state of the ExpansionTile. To address this, use a GlobalKey on the ExpansionTile.
• ExpansionTileController controller issues: The controller property may not function as expected when the ExpansionTile modifies the widget tree during a rebuild. To resolve this, use a GlobalKey or delegate the management of the controller to ExpansionTileList by using ExpansionTileItemController type as a controller.

  Failed assertion: line 607 pos 12: 'widget.controller?._state == null': is not true.

• ExpansionTileController controller methods may throw an assertion error when the widget is not yet mounted or initialized, mostly due to item not visible in scroll viewport. To resolve this, always check for init state controller.isInitialized before calling the controller methods.

• Using a ListView or ScrollView within the ExpansionTile children may cause layout issues. To resolve this, use a Column or Container with a fixed height as parent to the ListView and use a PageStorageKey(index) on the ListView.

The following _TypeError was thrown building ListView(scrollDirection: vertical, dependencies: [MediaQuery]): type 'bool' is not a subtype of type 'double?' in type cast

These issues are due to the ExpansionTile widget limitations and not the package. We have ensured that the package works as expected with the Flutter framework and made sure to take a safe decision to mitigate these issues. This means no issues should be encountered when using the package as intended.

Contributing

Contributions are welcome! If you find a bug or want a feature, please fill an issue. If you want to contribute code, please submit a pull request. We welcome contributions from everyone. Before you start:

1. Fork the repository to your own GitHub account.
2. Clone the project to your machine.
3. Create a branch locally with a descriptive name.
4. Commit changes to the branch.
5. Push changes to your fork.
6. Create a new pull request in GitHub and link the issue you are fixing.

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License

This project is licensed under the BSD-style license. See the file for details.

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