prefer_spacing

v0.4.0WarningConfigurableWidget Best Practices

This rule detects SizedBox widgets used as uniform spacers between children in a Row, Column, or Flex, and suggests using the built-in spacing argument instead. It also catches separatedBy() and .expand() patterns that insert SizedBox spacers. Requires Flutter 3.27+.

Why use this rule

Scattering SizedBox(height: 10) between every child is verbose and easy to get wrong (miss one, use a different value, etc.). The spacing parameter on Row, Column, and Flex applies uniform spacing declaratively with a single property, making the intent clear and the code shorter. It also avoids polluting the children list with non-semantic spacer widgets.

See also: Column spacing

Don’t

Column(
  children: [
    Text('First'),
    SizedBox(height: 10),
    Text('Second'),
    SizedBox(height: 10),
    Text('Third'),
  ],
)

Do

Column(
  spacing: 10,
  children: [Text('First'), Text('Second'), Text('Third')],
)

Turning this rule off

This rule is in the opinionated preset, so it is on with preset: opinionated, or by name:

many_lints.yaml

rules:
  prefer_spacing: true

To turn it off again:

many_lints.yaml

rules:
  prefer_spacing: false

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

Options

analysis_options.yaml

analysis_options.yaml

many_lints:
  rules:
    prefer_spacing:
      min_children: 5

many_lints.yaml

many_lints.yaml

rules:
  prefer_spacing:
    min_children: 5

Option	Type	Default	Description
min_children	int	3	Minimum number of children in the list before spacers are reported

Related rules

• use_gap — Opposing convention. Use Gap widget instead of SizedBox for spacing in multi-child widgets.
• avoid_expanded_as_spacer — Use Spacer instead of Expanded with an empty child.
• always_pass_global_key — Don’t create a GlobalKey inside build.
• avoid_conditional_hooks — Never call hooks inside conditionals, loops, or ternaries.