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avoid-returning-widgets

added in: 1.6.0
warning
⚙️
Free+

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.

⚙️ Config​

Set ignored-names (default is empty) to ignore a function or method name.

Set ignored-annotations (default is [FunctionalWidget, swidget, hwidget, hcwidget]) to override the default list of ignored annotations.

Set allow-nullable (default is false) to allow functions or methods with the nullable return type (example).

analysis_options.yaml
dart_code_metrics:
  rules:
    - avoid-returning-widgets:
        ignored-names:
          - testFunction
        ignored-annotations:
          - allowedAnnotation
        allow-nullable: false

Example​

❌ Bad:

class MyWidget extends StatelessWidget {
  const MyWidget();

  // LINT: Avoid returning widgets from a getter. Try replacing this getter with a stateless widget.
  Widget get _someWidget => Container();

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

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        Text('Text!'),
        ...
        // LINT: Avoid returning widgets from a function. Try replacing this function with a stateless widget.
        _buildShinyWidget(),
      ],
    );
  }
}

✅ 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, // Correct, used in a builder
    );
  }
}

Example with "allow-nullable"​

Config
analysis_options.yaml
dart_code_metrics:
  rules:
    - avoid-returning-widgets:
        allow-nullable: true

✅ Good:

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        Text('Text!'),
        ...
        // Correct, allowed
        if (_globalBuildMyWidget() != null) _globalBuildMyWidget(),
      ],
    );
  }
}

Widget? _globalBuildMyWidget() {
  return Container();
}

Additional Resources​