Step 2: Subclass StatefulWidget

lib/main.dart (FavoriteWidget)

Note:
  Members or classes that start with an underscore
  (_) are private. For more information,
  see Libraries and imports, a section in the
  Dart language documentation.

Step 3: Subclass State

The _FavoriteWidgetState class stores the mutable data
that can change over the lifetime of the widget.
When the app first launches, the UI displays a solid
red star, indicating that the lake has “favorite” status,
along with 41 likes. These values are stored in the
_isFavorited and _favoriteCount fields:

lib/main.dart (_FavoriteWidgetState fields)

bool _isFavorited = true;

int _favoriteCount = 41;

  // ···
}

IconButton (instead of