Displaying notification badge on BottomNavigationBar's Icon

Question

One more variation of counting badge (implemented with Stack of Icon and wrapped in Container Text, which stretched when counter increase):

BottomNavigationBarItem(
  icon: new Stack(
    children: <Widget>[
      new Icon(Icons.notifications),
      new Positioned(
        right: 0,
        child: new Container(
          padding: EdgeInsets.all(1),
          decoration: new BoxDecoration(
            color: Colors.red,
            borderRadius: BorderRadius.circular(6),
          ),
          constraints: BoxConstraints(
            minWidth: 12,
            minHeight: 12,
          ),
          child: new Text(
            '$_counter',
            style: new TextStyle(
              color: Colors.white,
              fontSize: 8,
            ),
            textAlign: TextAlign.center,
          ),
        ),
      )
    ],
  ),
  title: Text('Notifications'),
),

Yes. It can be done by stacking two icons using the Stack and Positioned widget.

      new BottomNavigationBarItem(
        title: new Text('Home'),
        icon: new Stack(
          children: <Widget>[
            new Icon(Icons.home),
            new Positioned(  // draw a red marble
              top: 0.0,
              right: 0.0,
              child: new Icon(Icons.brightness_1, size: 8.0, 
                color: Colors.redAccent),
            )
          ]
        ),
      )

If you also want to handle onTap with some splash, use this widget, you can further customize it according to your needs:

Copy this class:

class NamedIcon extends StatelessWidget {
  final IconData iconData;
  final String text;
  final VoidCallback onTap;
  final int notificationCount;

  const NamedIcon({
    Key key,
    this.onTap,
    @required this.text,
    @required this.iconData,
    this.notificationCount,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return InkWell(
      onTap: onTap,
      child: Container(
        width: 72,
        padding: const EdgeInsets.symmetric(horizontal: 8),
        child: Stack(
          alignment: Alignment.center,
          children: [
            Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Icon(iconData),
                Text(text, overflow: TextOverflow.ellipsis),
              ],
            ),
            Positioned(
              top: 0,
              right: 0,
              child: Container(
                padding: EdgeInsets.symmetric(horizontal: 6, vertical: 2),
                decoration: BoxDecoration(shape: BoxShape.circle, color: Colors.red),
                alignment: Alignment.center,
                child: Text('$notificationCount'),
              ),
            )
          ],
        ),
      ),
    );
  }
}

---

Usage:

Scaffold(
  appBar: AppBar(
    title: Text('AppBar'),
    actions: [
      NamedIcon(
        text: 'Inbox',
        iconData: Icons.notifications,
        notificationCount: 11,
        onTap: () {},
      ),
      NamedIcon(
        text: 'Mails',
        iconData: Icons.mail,
        notificationCount: 1,
        onTap: () {},
      ),
    ],
  ),
)

There is a nice package[0] that makes this as simple as using the following instead of an Icon:

Badge(
  badgeContent: Text('3'),
  child: Icon(Icons.settings),
)

0: https://pub.dev/packages/badges