prefer_transform_over_container

v0.4.0 Warning Fix Widget Replacement

Flags Container widgets that only use the transform parameter (plus optional key and child). When Container is used solely for a transform, the Transform widget is a lighter, more descriptive alternative.

Points the opposite way from prefer_container

This rule replaces a single-parameter Container with the specific widget, while prefer_container collapses 3 or more nested layout widgets into a Container.

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

Container is a convenience widget that composes many lower-level widgets internally. When you only need a matrix transform, using Transform directly avoids the overhead and clearly communicates your intent. It also gives you access to Transform’s named constructors like Transform.rotate and Transform.scale.

See also: Transform | Container

Don’t

// Container with only transform parameter
Container(
  transform: Matrix4.rotationZ(math.pi / 6)..rotateX(0.15),
  child: const Text('Skewed'),
);

// Container with only transform and key
Container(
  key: const ValueKey('rotated'),
  transform: Matrix4.rotationZ(math.pi / 4),
  child: const Text('Rotated'),
);

Do

// Use Transform directly
Transform(
  transform: Matrix4.rotationZ(math.pi / 6)..rotateX(0.15),
  child: const Text('Skewed'),
);

// Container with transform and other parameters is fine
Container(
  transform: Matrix4.rotationZ(math.pi / 4),
  alignment: Alignment.topRight,
  child: const Text('Rotated with alignment'),
);

Configuration

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

many_lints.yaml

rules:
  prefer_transform_over_container: true

To turn it off again:

many_lints.yaml

rules:
  prefer_transform_over_container: false

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

Related rules

• prefer_container — Opposing convention. Replace sequences of nested widgets with a single Container.
• prefer_align_over_container — Use Align instead of Container when only alignment is set.
• prefer_constrained_box_over_container — Use ConstrainedBox instead of Container when only constraints is set.
• prefer_padding_over_container — Use Padding instead of Container when only padding or margin is set.