prefer_padding_over_container

v0.1.0 Warning Fix Widget Replacement

Flags Container widgets that only use the padding or margin parameter (plus optional key and child). When Container is used solely for spacing, the Padding 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 composes half a dozen widgets internally; when the only argument is padding or margin, Padding does the same job in one render object. The quick fix does the rewrite for you — it renames the constructor and, for a margin, renames the argument too.

See also: Padding | Container

Don’t

// A Container used purely to inset a label.
Container(padding: EdgeInsets.all(16), child: Text('Hello'));

Do

Padding(padding: EdgeInsets.all(16), child: Text('Hello'));

Examples

margin: becomes padding:

On a Container with nothing else set, margin and padding render identically — the margin has no decoration or colour to sit outside of. So the fix renames the argument as it swaps the widget:

// Don't
Container(margin: EdgeInsets.all(16), child: Text('Hello'));

// Do
Padding(padding: EdgeInsets.all(16), child: Text('Hello'));

No child is still reported

Padding takes an optional child too, so a childless spacer converts the same way:

// Don't
Container(margin: EdgeInsets.symmetric(horizontal: 8));

// Do
Padding(padding: EdgeInsets.symmetric(horizontal: 8));

Known limitations

padding and margin together is not reported. Those two are no longer equivalent once both exist — the fix would have to merge them — so the rule stays quiet:

// Not reported
Container(padding: EdgeInsets.all(8), margin: EdgeInsets.all(8));

Any other argument stops it. width, color, decoration, alignment — one of them and Container is doing something Padding cannot:

// Not reported
Container(padding: EdgeInsets.all(8), width: 100, child: Text('Hello'));

key and child are the two exceptions; they do not count against the rule.

Configuration

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

many_lints.yaml

rules:
  prefer_padding_over_container: true

To turn it off again:

many_lints.yaml

rules:
  prefer_padding_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_transform_over_container — Use Transform instead of Container when only transform is set.