A Flex (i.e. Column or Row) that sizes itself to its main child in the cross axis direction.


This package contains three classes:

  • FlexWithMainChild
  • ColumnWithMainChild
  • RowWithMainChild

Getting started

Add flex_with_main_child: <version> under dependencies in your pubspec.yaml.

How it works

After it renders, it check if the crossAxisSize of the flex is the same as the size obtain from mainChildKey. If not, it'll render again with the crossAxisSize set to the size previously measured from mainChildKey. It'll keep rerendering until the size matches.


The 3 classes' usage are exactly identical to their counterparts in flutter/widgets.dart, except they take in a mainChildKey which they will use to match their cross axis size to.


Widget build(BuildContext context) {
  final mainChildKey = GlobalKey();

  return ColumnWithMainChild(
    // ColumnWithMainChild have the same parameters as Column
    mainAxisAlignment: MainAxisAlignment.center,
    // except children, obviously.
    children: [
      // Because the underlying implementation uses Flex, any child that work
      // in Column will work exactly the same way in ColumnWithMainChild.
      Spacer(flex: 5),
      Text('very very very very long description'),
        'short Title',
        key: mainChildKey, // you have to give mainChildKey to the main child
      Text('another very very very very very long text'),
      Spacer(flex: 10),
    mainChildKey: mainChildKey,

The above code will give:

Additional information

Note that SizedBox sometimes will be forced to fit parent (e.g. when the parent is the screen). When this happen, place the FlexWithMainChild into a Center or some other intermediate containers.

Contribution & bug report

All pull requests / issues are welcome.


A package that provide Flex (and Row and Column) that match its size in the cross axis direction with a specific child.