Observer<T> class

A widget that rebuilds when a reactive variable changes.

Observer automatically listens to a Reactive variable and rebuilds its child widget whenever the variable's value changes. This provides a declarative way to create reactive UI without manually managing listeners.

The widget is lightweight and efficient, using Flutter's ValueListenableBuilder internally for optimal performance.

Example:

final counter = Reactive<int>(0);

Observer<int>(
  listenable: counter,
  listener: (value) => Text('Count: $value'),
);

// Updates automatically when counter changes
counter.value++;

For nullable types, use ObserverN instead.