prefer_container

v0.4.0WarningFixConfigurableWidget Replacement

Flags chains of 3 or more nested widgets that can all be replaced with a single Container widget. Container internally composes Align, Padding, DecoratedBox, ConstrainedBox, Transform, ColoredBox, SizedBox, and other layout widgets — so nesting them individually is redundant.

The collapsible set is exactly Padding, Align, Center, ColoredBox, DecoratedBox, ConstrainedBox, SizedBox, Transform, ClipRRect, ClipOval, ClipPath, and FractionallySizedBox. Widgets Container cannot express — notably Opacity, IntrinsicHeight, IntrinsicWidth, and LimitedBox — are excluded, and a chain containing one of them is split rather than collapsed across it.

Points the opposite way from the prefer_*_over_container rules

This rule collapses 3 or more nested layout widgets into a Container, while prefer_padding_over_container, prefer_align_over_container, prefer_constrained_box_over_container, and prefer_transform_over_container replace a single-parameter Container with the specific widget.

The thresholds keep them from firing on the same code, but after further edits a fix from one rule can produce code the other flags. If that churn bothers you, enable only one direction.

The SDK’s avoid_unnecessary_containers is a third, non-overlapping case: it removes a Container that has no parameters at all.

Why use this rule

Deeply nested single-purpose widgets make the widget tree harder to read and debug. When three or more of these widgets are stacked, collapsing them into a single Container reduces nesting, improves readability, and still gives you access to all the same properties. The rule only triggers when there are no conflicting parameters (e.g., two Padding widgets would conflict).

See also: Container | DecoratedBox | SizedBox | Dart lint: avoid_unnecessary_containers

Don’t

// Transform > Padding > Align can be replaced with Container
Transform(
  transform: Matrix4.identity(),
  child: Padding(
    padding: EdgeInsets.all(16),
    child: Align(alignment: Alignment.center, child: Text('Hello')),
  ),
);

// Padding > ColoredBox > SizedBox can be replaced with Container
Padding(
  padding: EdgeInsets.all(8),
  child: ColoredBox(
    color: Colors.red,
    child: SizedBox(width: 100, height: 50, child: Text('World')),
  ),
);

Do

// Single Container combines all properties
Container(
  transform: Matrix4.identity(),
  padding: EdgeInsets.all(16),
  alignment: Alignment.center,
  child: Text('Hello'),
);

// Single Container with color and size
Container(
  padding: EdgeInsets.all(8),
  color: Colors.red,
  width: 100,
  height: 50,
  child: Text('World'),
);

// Only 2 nested widgets (below threshold) is fine
Padding(
  padding: EdgeInsets.all(8),
  child: Align(alignment: Alignment.center, child: Text('OK')),
);

Turning this rule off

This rule is in no preset, so it is off unless you enable it by name:

many_lints.yaml

rules:
  prefer_container: true

To turn it off again:

many_lints.yaml

rules:
  prefer_container: 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_container:
      min_sequence: 4

many_lints.yaml

many_lints.yaml

rules:
  prefer_container:
    min_sequence: 4

Option	Type	Default	Description
min_sequence	int	3	Minimum number of consecutive Container-compatible widgets in a nesting chain before the rule reports

Raise it to only flag deeper nesting; lower it to 2 to catch every collapsible pair.

Related rules

• prefer_align_over_container — Opposing convention. Use Align instead of Container when only alignment is set.
• prefer_constrained_box_over_container — Opposing convention. Use ConstrainedBox instead of Container when only constraints is set.
• prefer_padding_over_container — Opposing convention. Use Padding instead of Container when only padding or margin is set.
• prefer_transform_over_container — Opposing convention. Use Transform instead of Container when only transform is set.