How can I align nested lists in Flutter?

Question

I want align the following nested list in such a way that black line should be horizontally center of the green box (parent list) i cant add any padding or extra space or positioned or increase the red column width

please note black line is for reference the line actually not part of the code

dartpad ready code here

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Horizontal List of Vertical Lists')),
        body: ParentLayout(),
      ),
    );
  }
}

class ParentLayout extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        // Header content (Green Box at the top)
        Container(
          height: 100,
          width: 200,
        
          color: Colors.green[100],
          child: Center(child: Text("Parent ListView Content Above")),
        ),

        // Horizontal layout with dividing line centered to green boxes
        Expanded(
          child: Row(
            mainAxisAlignment: MainAxisAlignment.center,
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              // Blue List
              _generateBlueList(),

              // Dividing line
     
              // Red List
              _generateRedList(),
            ],
          ),
        ),

        // Footer content (Green Box at the bottom)
        Container(
          height: 100,
          width: 200,
          color: Colors.green[100],
          child: Center(child: Text("Parent ListView Content Below")),
        ),
      ],
    );
  }

  // Generate blue list with varying sizes
  Widget _generateBlueList() {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: List.generate(
        5,
        (innerIndex) => Container(
          height: 40 + (innerIndex * 25), // Varying height
          width: 80 + (innerIndex * 40), // Varying width
          color: Colors.blue[100 * (innerIndex + 1)],
          child: Center(
            child: Text(
              'Blue $innerIndex',
              style: TextStyle(color: Colors.white),
            ),
          ),
        ),
      ),
    );
  }

  // Generate red list with fixed sizes
  Widget _generateRedList() {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: List.generate(
        5,
        (innerIndex) => Container(
          height: 60, // Fixed height
          width: 100, // Fixed width
          color: Colors.red[100 * (innerIndex + 1)],
          child: Center(
            child: Text(
              'Red $innerIndex',
              style: TextStyle(color: Colors.white),
            ),
          ),
        ),
      ),
    );
  }
}

Answer 1

I did bit of math to find necessary x axis translate, and achieved it.

to make the other neighbouring widget respect the translated widget position, im adding padding to entire parent column. And its not wasting the space, because transformed widget is laying there.

[![import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Dynamic Horizontal List')),
        body: ParentLayout(),
      ),
    );
  }
}

class ParentLayout extends StatefulWidget {
  @override
  _ParentLayoutState createState() => _ParentLayoutState();
}

class _ParentLayoutState extends State<ParentLayout> {
  final GlobalKey _blueKey = GlobalKey();
  final GlobalKey _redKey = GlobalKey();

  double _blueListWidth = 0;
  double _redListWidth = 0;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((_) => _updateWidths());
  }

  void _updateWidths() {
    final blueRenderBox = _blueKey.currentContext?.findRenderObject() as RenderBox?;
    final redRenderBox = _redKey.currentContext?.findRenderObject() as RenderBox?;

    if (blueRenderBox != null && redRenderBox != null) {
      final double newBlueListWidth = blueRenderBox.size.width;
      final double newRedListWidth = redRenderBox.size.width;

      // Update state only if widths have changed
      if (_blueListWidth != newBlueListWidth || _redListWidth != newRedListWidth) {
        setState(() {
          _blueListWidth = newBlueListWidth;
          _redListWidth = newRedListWidth;
        });
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    // Calculate the translation for the entire row based on which list is wider
    final double rowTranslation = (_blueListWidth > _redListWidth)
        ? -((_blueListWidth - _redListWidth) / 2) // Translate left if blue is wider
        : ((_redListWidth - _blueListWidth) / 2); // Translate right if red is wider

    // Calculate dynamic padding for the parent list view
    final EdgeInsets parentPadding = EdgeInsets.only(
      left: rowTranslation < 0 ? rowTranslation.abs() : 0, // Padding on left
      right: rowTranslation > 0 ? rowTranslation.abs() : 0, // Padding on right
    );

    return Padding(
      padding: parentPadding, // Apply dynamic padding
      child: Column(
        children: \[
          // Header content (Green Box at the top)
          Container(
            height: 100,
            width: 200,
            color: Colors.green\[100\],
            child: Center(child: Text("Parent ListView Content Above")),
          ),

          // Horizontal layout with dividing line centered to green boxes
          IntrinsicHeight(
            child: Transform.translate(
              offset: Offset(rowTranslation, 0), // Translate based on the width difference
              child: Row(
                mainAxisAlignment: MainAxisAlignment.center,
                mainAxisSize: MainAxisSize.min,
                crossAxisAlignment: CrossAxisAlignment.start, // Align to the top of the Row
                children: \[
                  // Blue List wrapped in IntrinsicWidth
                  IntrinsicWidth(
                    child: Container(
                      key: _blueKey,
                      color: Colors.blue.withOpacity(0.2), // Background for visual distinction
                      child: _generateBlueList(),
                    ),
                  ),

                  // Divider
                  Container(
                    width: 2,
                    color: Colors.grey,
                    margin: EdgeInsets.symmetric(horizontal: 8),
                  ),

                  // Red List wrapped in IntrinsicWidth
                  IntrinsicWidth(
                    child: Container(
                      key: _redKey,
                      color: Colors.red.withOpacity(0.2), // Background for visual distinction
                      child: _generateRedList(),
                    ),
                  ),
                \],
              ),
            ),
          ),

          // Footer content (Green Box at the bottom)
          Container(
            height: 100,
            width: 200,
            color: Colors.green\[100\],
            child: Center(child: Text("Parent ListView Content Below")),
          ),
        \],
      ),
    );
  }

  // Generate blue list with varying sizes
  Widget _generateBlueList() {
    return Column(
      mainAxisAlignment: MainAxisAlignment.start, // Align items to the top
      children: List.generate(
        5,
        (innerIndex) => Container(
          height: 40 + (innerIndex * 25), // Varying height
          width: 80 + (innerIndex * 40), // Varying width
          color: Colors.blue\[100 * (innerIndex + 1)\],
          child: Center(
            child: Text(
              'Blue $innerIndex',
              style: TextStyle(color: Colors.white),
            ),
          ),
        ),
      ),
    );
  }

  // Generate red list with fixed sizes
  Widget _generateRedList() {
    return Column(
      mainAxisAlignment: MainAxisAlignment.start, // Align items to the top
      children: List.generate(
        5,
        (innerIndex) => Container(
          height: 60, // Fixed height
          width: 100, // Fixed width
          color: Colors.red\[100 * (innerIndex + 1)\],
          child: Center(
            child: Text(
              'Red $innerIndex',
              style: TextStyle(color: Colors.white),
            ),
          ),
        ),
      ),
    );
  }
}