How to Change border color of Radio widget in Flutter?

Question

What I Currently Have

What I want to achieve

The Code that I have now

Radio(
   value: 2,
   groupValue: val,
   onChanged: (value) {
   setState(() {
      val = value;
      });
   },
  activeColor: secondaryColor,)

Answer 1

It's not possible to customize that much the Radio button. The only color parameter for the button is fillColor. It will impact both the inner plain circle and the outer circle.

If you really want a custom look you'll need to build your own widget. Here is a simple example that you can customize and improve. You could also try to start from the source code of the flutter Radio widget.

class CustomRadio extends StatefulWidget {
  final int value;
  final int groupValue;
  final void Function(int) onChanged;
  const CustomRadio({Key? key, required this.value, required this.groupValue, required this.onChanged})
      : super(key: key);

  @override
  _CustomRadioState createState() => _CustomRadioState();
}

class _CustomRadioState extends State<CustomRadio> {
  @override
  Widget build(BuildContext context) {
    bool selected = (widget.value == widget.groupValue);

    return InkWell(
      onTap: () => widget.onChanged(widget.value),
      child: Container(
        margin: const EdgeInsets.all(4),
        padding: const EdgeInsets.all(4),
        decoration: BoxDecoration(shape: BoxShape.circle, color: selected ? Colors.white : Colors.grey[200]),
        child: Icon(
          Icons.circle,
          size: 30,
          color: selected ? Colors.deepPurple : Colors.grey[200],
        ),
      ),
    );
  }
}

Result :

Answer 2

There is no way to provide the color of the outer circle in the material Radio class, what you can do is to create your own radio Button, either from scratch (Check the @Tanguy answer)or you copy the Radio class and change its design/behavior. If you decide to copy the Radio class you need to inherit from the Radio so it can work with the rest of the Material design elements. Here is a copy of it https://gist.github.com/karimkod/8f7c93da798670c8b6e9b85ff9fb5383 You can change the paint method of The _RadioPainter class to draw basically whatever you want. I have changed it in the gist to look purple.