falcon

Rules / Correctness / avoid-returning-widgets

avoid-returning-widgets

lint/correctness/avoid-returning-widgets
recommendedflutter
Same as avoid-returning-widgets · Dart Code Metrics

Disallow functions and methods that return a Widget.

Flags a function, method, or getter whose return type is Widget, StatelessWidget, or StatefulWidget (or a Future, Stream, or Completer of one). Returning a widget from a helper instead of defining a real widget class defeats Flutter's element tree: the returned subtree cannot hold its own state, is rebuilt wholesale whenever the enclosing build runs, and never appears as a distinct node in the widget inspector. Extract the subtree into its own StatelessWidget or StatefulWidget so Flutter can cache and rebuild it independently. The build method and @override members are exempt, as is any return type naming a concrete widget subclass such as Container.

Invalid

example.dartdart
// Test cases for avoid-returning-widgets rule
// Flags methods that return Widget type outside of build methods

import 'package:flutter/material.dart';

class MyScreen extends StatelessWidget {
  Widget _buildCard() {
    return Card(
      child: Text('Hello'),
    );
  }

  Widget _buildButton() {
    return ElevatedButton(
      onPressed: () {},
      child: Text('Click me'),
    );
  }

  Widget buildHeader(String title) {
    return Container(
      child: Text(title),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: _buildCard(),
    );
  }
}

class WidgetHelper {
  static Widget createCard() {
    return Card(child: SizedBox());
  }

  static Widget createRow(List<Widget> children) {
    return Row(children: children);
  }
}

Widget globalWidgetBuilder() {
  return Container();
}

Future<Widget> asyncWidgetBuilder() {
  return Future.value(Text('async'));
}
Methods should not return Widget directly; extract to a separate widget class
6class MyScreen extends StatelessWidget {
7 Widget _buildCard() {
Methods should not return Widget directly; extract to a separate widget class
12
13 Widget _buildButton() {
Methods should not return Widget directly; extract to a separate widget class
19
20 Widget buildHeader(String title) {
Methods should not return Widget directly; extract to a separate widget class
34class WidgetHelper {
35 static Widget createCard() {
Methods should not return Widget directly; extract to a separate widget class
38
39 static Widget createRow(List<Widget> children) {
Functions should not return Widget directly; extract to a separate widget class
43
44Widget globalWidgetBuilder() {
Functions should not return Widget directly; extract to a separate widget class
47
48Future<Widget> asyncWidgetBuilder() {

Valid

example.dartdart
// Good examples for avoid-returning-widgets rule
// Using separate widget classes instead of methods that return widgets

import 'package:flutter/material.dart';

class MyScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: MyCard(),
      appBar: AppBar(
        title: MyHeader(title: 'Title'),
      ),
    );
  }
}

class MyCard extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Card(
      child: Text('Hello'),
    );
  }
}

class MyButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: () {},
      child: Text('Click me'),
    );
  }
}

class MyHeader extends StatelessWidget {
  final String title;

  MyHeader({required this.title});

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Text(title),
    );
  }
}

class WidgetHelper {
  static Card createCard() {
    return Card(child: SizedBox());
  }

  static List<Widget> getChildren() {
    return [Text('a'), Text('b')];
  }
}

void processData(String data) {
  print(data);
}

String buildString() {
  return "not a widget";
}

How to configure

Set the severity of avoid-returning-widgets in your falcon.json:

falcon.jsonjson
{
  "linter": {
    "rules": {
      "correctness": {
        "avoid-returning-widgets": "error"
      }
    }
  }
}

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