useEffect<T> function

void useEffect<T>(NullableVoidCallback callback, [ List<T>? dependencies ])

Accepts a function that contains imperative, possibly effect-full code.

Mutations, subscriptions, timers, logging, and other side effects are not allowed inside the main body of a function widget (referred to as Rad's render phase). Doing so will lead to confusing bugs and inconsistencies in the UI.

By default, effects run after every completed render, but you can choose to fire them only when certain values have changed.

Cleaning up an effect

Often, effects create resources that need to be cleaned up before the scope leaves the screen, such as a subscription or timer ID. To do this, the function passed to useEffect can return a clean-up function.

The clean-up function runs after the scope is removed from the UI to prevent memory leaks. Additionally, if scope renders multiple times (as they typically do), the previous effect is cleaned up before executing the next effect.

Implementation

void useEffect<T>(
  NullableVoidCallback callback, [
  List<T>? dependencies,
]) {
  var useEffectHook = useHook();
  useEffectHook ??= setupHook(_UseEffectHook<T>());

  if (useEffectHook is! _UseEffectHook) {
    throw Exception(
      'Expecting hook of type: $_UseEffectHook '
      'but got: ${useEffectHook.runtimeType}. '
      'Please make sure your hooks call order is not dynamic.',
    );
  }

  useEffectHook
    ..updateDependencies(dependencies)
    ..updateEffectCallback(callback);
}