Add complex example of Observer pattern, connected to Flutter application.

[ilopX]

Observer pattern

Observer is a behavioral design pattern that lets you define a subscription mechanism to notify
multiple objects about any events that happen to the object they’re observing.

Tutorial: here.

Subscriber Flutter Widget example

This is a complex example of an Observer pattern, connected to a Flutter application. The example includes, the previously implemented AppObserver example pattern, which you can see here.

Online demo:

Click on the picture to see the demo.

Diagram:

Sequence

Client code:

void main() {
    // widget that generates a new event
    ElevatedButton(
      child: Text('Generate new hash'),
      onPressed: () {
        final hash = 'some hash';
        observer.notify(NewHashEvent(hash));
      },
    );
    
    // widget event consumer NewHashEvent
    SubscriberWidget<NewHashEvent>(
      observer: observer,
      builder: (context, event) {
        return Text(
          event?.newHash ?? 'Hash no generated' ,
        );
      },
    );
}