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Many Lints

prefer_single_setstate

v0.4.0WarningFixConfigurableCode Quality

Flags methods in State subclasses that contain multiple setState() calls at the same scope level. Each setState() call schedules a rebuild, so calling it multiple times in the same synchronous method triggers redundant rebuilds that can be avoided by merging all state mutations into a single call.

Why use this rule

Section titled “Why use this rule”

Multiple setState() calls in the same method cause Flutter to schedule multiple rebuilds in the same frame. While Flutter coalesces them into one actual rebuild, the pattern is misleading and fragile. Merging mutations into a single setState() makes the code clearer and avoids accidental intermediate states if the framework behavior changes.

See also: State.setState()

Don’t

Section titled “Don’t”
class _BadState extends State<BadWidget> {
  String _a = '';
  String _b = '';


  void _update() {
    setState(() {
      _a = 'Hello';
    });
    setState(() {
      _b = 'World';
    });
  }


  // Even with code in between:
  void _updateWithGap() {
    setState(() {
      _a = 'Hello';
    });
    debugPrint('between');
    setState(() {
      _b = 'World';
    });
  }
}

Do

Section titled “Do”
class _GoodState extends State<GoodWidget> {
  String _a = '';
  String _b = '';


  void _update() {
    setState(() {
      _a = 'Hello';
      _b = 'World';
    });
  }
}


// setState in separate closures is fine (different scopes):
void _setup() {
  final callback1 = () {
    setState(() { _data = 'a'; });
  };
  final callback2 = () {
    setState(() { _data = 'b'; });
  };
}


// setState in different methods is fine:
void _update1() {
  setState(() { _data = 'Hello'; });
}
void _update2() {
  setState(() { _data = 'World'; });
}

Turning this rule off

Section titled “Turning this rule off”

This rule is in the opinionated preset, so it is on with preset: opinionated, or by name:

many_lints.yaml
rules:
  prefer_single_setstate: true

To turn it off again:

many_lints.yaml
rules:
  prefer_single_setstate: false

To keep the rule on but skip certain paths, use per-rule exclude.

Options

Section titled “Options”

Projects with a state abstraction that does not extend Flutter’s State can opt that base class into this rule:

analysis_options.yaml
many_lints:
  rules:
    prefer_single_setstate:
      state_base_classes: [AppState]
Option Type Default Description
state_base_classes list of strings [] Additional non-State base classes whose subclasses should be treated as state classes
Section titled “Related rules”