avoid-returning-widgets

added in: 3.1.0

warning

⚙️

Warns when a method, function or getter returns a Widget or subclass of a Widget.

Extracting widgets to a method is considered as a Flutter anti-pattern, because when Flutter rebuilds widget tree, it calls the function all the time, making more processor time for the operations.

Consider creating a separate widget instead of a function or method.

info

The following patterns will not trigger the rule:

• Widget build method overrides.
• Class method that is passed to a builder.
• Functions with functional_widget package annotations.

Additional resources:

• https://github.com/flutter/flutter/issues/19269
• https://flutter.dev/docs/perf/rendering/best-practices#controlling-build-cost
• https://www.reddit.com/r/FlutterDev/comments/avhvco/extracting_widgets_to_a_function_is_not_an/
• https://medium.com/flutter-community/splitting-widgets-to-methods-is-a-performance-antipattern-16aa3fb4026c

Use ignored-names configuration, if you want to ignore a function or method name.

Use ignored-annotations configuration, if you want to override default ignored annotation list.

⚙️ Config example

dart_code_metrics:
  ...
  rules:
    ...
    - avoid-returning-widgets:
        ignored-names:
          - testFunction
        ignored-annotations:
          - allowedAnnotation

will ignore all functions named testFunction and all functions having allowedAnnotation annotation.

Example

❌ Bad:

class MyWidget extends StatelessWidget {
  const MyWidget();

  // LINT
  Widget _getWidget() => Container();

  Widget _buildShinyWidget() {
    return Container(
      child: Column(
        children: [
          Text('Hello'),
          ...
        ],
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        Text('Text!'),
        ...
        _buildShinyWidget(), // LINT
      ],
    );
  }
}

✅ Good:

class MyWidget extends StatelessWidget {
  const MyWidget();

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        Text('Text!'),
        ...
        const _MyShinyWidget(),
      ],
    );
  }
}

class _MyShinyWidget extends StatelessWidget {
  const _MyShinyWidget();

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Column(
        children: [
          Text('Hello'),
          ...
        ],
      ),
    );
  }
}

✅ Good:

class MyWidget extends StatelessWidget {
  Widget _buildMyWidget(BuildContext context) {
    return Container();
  }

  @override
  Widget build(BuildContext context) {
    return Builder(
      builder: _buildMyWidget,
    );
  }
}