Flutter rounded TabBar border indicator

You must create your own Decoration. Have a look to this guide : https://medium.com/swlh/flutter-custom-tab-indicator-for-tabbar-d72bbc6c9d0c

It creates a custom point under the tab, so you can copy that to create your kind of indicator

Thanks, BabC.

Here's the final result:

class _TabIndicator extends BoxDecoration {
  final BoxPainter _painter;

  _TabIndicator() : _painter = _TabIndicatorPainter();

  @override
  BoxPainter createBoxPainter([onChanged]) => _painter;
}

class _TabIndicatorPainter extends BoxPainter {
  final Paint _paint;

  _TabIndicatorPainter()
      : _paint = Paint()
          ..color = Colors.blue
          ..isAntiAlias = true;

  @override
  void paint(Canvas canvas, Offset offset, ImageConfiguration cfg) {
    final double _xPos = offset.dx + cfg.size.width / 2;

    canvas.drawRRect(
      RRect.fromRectAndCorners(
        Rect.fromLTRB(_xPos - 20, 0, _xPos + 20, 5),
        bottomLeft: const Radius.circular(5.0),
        bottomRight: const Radius.circular(5.0),
      ),
      _paint,
    );
  }
}