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avoid-unnecessary-setstate

added in: 1.6.0
warning
Pro+
preset: recommended

Warns when setState is called inside initState, didUpdateWidget or build methods and when it's called from a sync method that is called inside those methods.

Calling setState in such cases will result in additional widget re-rendering, which will negatively affect performance.

Consider changing state directly without calling setState.

Example​

❌ Bad:

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  String myString = '';

  @override
  void initState() {
    super.initState();

    // LINT: Avoid calling unnecessary 'setState'. Try changing the state directly.
    setState(() {
      myString = "Hello";
    });

    if (condition) {
      // LINT: Avoid calling unnecessary 'setState'. Try changing the state directly.
      setState(() {
        myString = "Hello";
      });
    }

    myStateUpdateMethod(); // LINT: Avoid calling sync methods that call 'setState'. Try changing the state directly.
  }

  @override
  void didUpdateWidget(MyWidget oldWidget) {
    // LINT: Avoid calling unnecessary 'setState'. Try changing the state directly.
    setState(() {
      myString = "Hello";
    });
  }

  void myStateUpdateMethod() {
    setState(() {
      myString = "Hello";
    });
  }

  @override
  Widget build(BuildContext context) {
    // LINT: Avoid calling unnecessary 'setState'. Try changing the state directly.
    setState(() {
      myString = "Hello";
    });

    if (condition) {
      // LINT: Avoid calling unnecessary 'setState'. Try changing the state directly.
      setState(() {
        myString = "Hello";
      });
    }

    myStateUpdateMethod(); // LINT: Avoid calling sync methods that call 'setState'. Try changing the state directly.

    return ElevatedButton(
      onPressed: () => myStateUpdateMethod(),
      onLongPress: () {
        setState(() {
          myString = data;
        });
      },
      child: Text('PRESS'),
    );
  }
}

✅ Good:

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  String myString = '';

  final classWithMethod = SomeClassWithMethod();

  @override
  void initState() {
    super.initState();

    myString = "Hello";

    classWithMethod.myMethod();
    myAsyncMethod();
  }

  @override
  void didUpdateWidget(MyWidget oldWidget) {
    myString = "Hello";
  }

  void myStateUpdateMethod() {
    setState(() {
      myString = "Hello";
    });
  }

  Future<void> myAsyncMethod() async {
    final data = await service.fetchData();

    setState(() {
      myString = data;
    });
  }

  @override
  Widget build(BuildContext context) {
    myAsyncMethod();

    return ElevatedButton(
      onPressed: () => myStateUpdateMethod(),
      onLongPress: () {
        setState(() {
          myString = data;
        });
      },
      child: Text('PRESS'),
    );
  }
}

Additional Resources​