avoid_expanded_as_spacer

v0.4.0 Warning Fix Widget Replacement

Flags Expanded widgets that wrap an empty SizedBox or Container as their child. This pattern is equivalent to using the Spacer widget, which is purpose-built for this exact use case.

Why use this rule

Flutter provides the Spacer widget specifically for creating flexible space in Row, Column, and Flex layouts. Using Expanded with an empty child obscures the intent and adds an unnecessary widget to the tree. Spacer is clearer, more concise, and immediately communicates that the purpose is to fill available space.

See also: Spacer | Expanded

Don’t

// Expanded with empty SizedBox
const Expanded(child: SizedBox());

// Expanded with empty Container
Expanded(child: Container());

// Expanded with flex and empty SizedBox
const Expanded(flex: 2, child: SizedBox());

Do

// Use Spacer directly
const Spacer();

// Use Spacer with flex parameter
const Spacer(flex: 2);

// Expanded with a non-empty child is fine
const Expanded(child: Text('content'));

Configuration

This rule is in the recommended preset, so it is on with preset: recommended or preset: opinionated. Add it to preset: core with avoid_expanded_as_spacer: true.

To turn it off:

many_lints.yaml

rules:
  avoid_expanded_as_spacer: false

To keep the rule on but skip certain paths, use per-rule exclude.

Related rules

• prefer_spacing — Use the spacing argument on Row/Column instead of SizedBox spacers.
• use_gap — Use Gap widget instead of SizedBox for spacing in multi-child widgets.
• avoid_border_all — Use Border.fromBorderSide instead of Border.all for const support.
• avoid_incorrect_image_opacity — Use Image’s opacity parameter instead of wrapping in Opacity.