useEffect function

void useEffect(Dispose? effect(), [ List<Object?>? keys ])

Useful for side-effects and optionally canceling them.

useEffect is called synchronously on every build, unless keys is specified. In which case useEffect is called again only if any value inside keys has changed.

It takes an effect callback and calls it synchronously. That effect may optionally return a function, which will be called when the effect is called again or if the widget is disposed.

By default effect is called on every build call, unless keys is specified. In which case, effect is called once on the first useEffect call and whenever something within keys change/

The following example call useEffect to subscribes to a Stream and cancels the subscription when the widget is disposed. Also if the Stream changes, it will cancel the listening on the previous Stream and listen to the new one.

Stream stream;
useEffect(() {
    final subscription = stream.listen(print);
    // This will cancel the subscription when the widget is disposed
    // or if the callback is called again.
    return subscription.cancel;
  },
  // when the stream changes, useEffect will call the callback again.
  [stream],
);

Implementation

void useEffect(Dispose? Function() effect, [List<Object?>? keys]) {
  use(_EffectHook(effect, keys));
}