avoid_unnecessary_setstate

A rule which 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.

Cases where setState is unnecessary:

• synchronous calls inside State lifecycle methods:
  • initState
  • didUpdateWidget
  • didChangeDependencies
• synchronous calls inside build method

Nested synchronous setState invocations are also disallowed.

Calling setState in the aforementioned methods is allowed for:

• async methods
• callbacks

Example:

BAD:

void initState() {
  setState(() => foo = 'bar');  // lint
  changeState();                // lint
}

void changeState() {
  setState(() => foo = 'bar');
}

void triggerFetch() async {
  await fetch();
  if (mounted) setState(() => foo = 'bar');
}

GOOD:

void initState() {
  triggerFetch();               // OK
  stream.listen((event) => setState(() => foo = event)); // OK
}

void changeState() {
  setState(() => foo = 'bar');
}

void triggerFetch() async {
  await fetch();
  if (mounted) setState(() => foo = 'bar');
}