Flutter Tabbarview underline color

Question

How to add underline to unselected tabs, like this:

https://ibb.co/mfkzKp

Here you can see it is gray colour for unselected tabs, and blue for selected.

Answer 1

I haven't found any reference in the documentation about how to customize disabled indicator. However, you can build your own widget that will take additional decoration parameter:

class DecoratedTabBar extends StatelessWidget implements PreferredSizeWidget {
  DecoratedTabBar({@required this.tabBar, @required this.decoration});

  final TabBar tabBar;
  final BoxDecoration decoration;

  @override
  Size get preferredSize => tabBar.preferredSize;

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        Positioned.fill(child: Container(decoration: decoration)),
        tabBar,
      ],
    );
  }
}

Then you can decorate your TabBar however you want:

appBar: AppBar(
  bottom: DecoratedTabBar(
    tabBar: TabBar(
      tabs: [
        // ...
      ],
    ),
    decoration: BoxDecoration(
      border: Border(
        bottom: BorderSide(
          color: Colors.blue,
          width: 2.0,
        ),
      ),
    ),
  ),
),

Which will result in desired behavior: