UseEffect constructor

UseEffect(Function callback, List<ReactterState> dependencies, [ Object? context ])

A ReactterHook that manages side-effect.

The side-effect logic into the callback function is executed when dependencies of ReactterState argument has changes or instance trigger LifeCycle.didMount event.

UseEffect(() {
  print("Execute by state changed or 'didMount' event");
}, [state], this);

If the callback returns a function, then UseEffect considers this as an effect cleanup.

The effect cleanup callback is executed, before callback is called or context trigger LifeCycle.willUnmount event:

UseEffect(() {
  print("Execute by 'didMount' event");

  return () {
    print("Execute by 'willUnmount' event");
  };
}, [], this);

RECOMMENDED: Use it on Object constructor:

class AppController {
  late final state = UseState(false);

  AppController() {
    UseEffect(() {
      print('state: ${state.value}');
    }, [state], this);

    Future.delayed(
      const Duration(seconds: 1),
      () {
        state.value = !state.value;
      },
    );
  }
}

If you need to execute the UseEffect's callback inmediately created, use dispatchEffect on context parameter:

UseEffect(
  () => print("Prompt execution or state changed"),
  [state],
  UseEffect.dispatchEffect,
);

or use mixin DispatchEffect:

class AppController with DispatchEffect {
  AppController() {
    UseEffect(
      () => print("Prompt execution or state changed"),
      [state],
      this,
    );
  }
}

If you not put instance on the context parameter, should to call dispose method to clear any UseEffect's events.

See also:

• ReactterState, it receives as dependencies.

Implementation

UseEffect(
  this.callback,
  this.dependencies, [
  this.context,
]) {
  _initialized = true;

  if (context == null) {
    _watchDependencies();
    return;
  }

  if (context is DispatchEffect) {
    _runCallbackAndWatchDependencies();
    return;
  }

  if (ReactterZone.current != null) return;

  final instance = _getInstance(context);

  if (instance != null) {
    attachTo(instance);
    return;
  }

  _watchDependencies();
}