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sized_box_for_whitespace

Lint rule

Use a 'SizedBox' to add whitespace to a layout.

Description

#

The analyzer produces this diagnostic when a Container is created using only the height and/or width arguments.

Example

#

The following code produces this diagnostic because the Container has only the width argument:

dart 
import 'package:flutter/material.dart';
​
Widget buildRow() {
  return Row(
    children: <Widget>[
      const Text('...'),
      Container(
        width: 4,
        child: Text('...'),
      ),
      const Expanded(
        child: Text('...'),
      ),
    ],
  );
}

Common fixes

#

Replace the Container with a SizedBox of the same dimensions:

dart 
import 'package:flutter/material.dart';
​
Widget buildRow() {
  return Row(
    children: <Widget>[
      Text('...'),
      SizedBox(
        width: 4,
        child: Text('...'),
      ),
      Expanded(
        child: Text('...'),
      ),
    ],
  );
}

Unless stated otherwise, the documentation on this site reflects Dart 3.9.2. Page last updated on 2025-9-1. View source or report an issue.