Can I use the width in a flutter widget

Question

I'm very new to Flutter so please bear with me. I wonder whether I can retrieve and use the width of a widget inside the build method. The RoundButton widget below illustrates two cases where having the width could be useful:

• to display the width as text
• to create a circular Container, I could use radius=width/2 (Note: I know this can be done using shape: BoxShape.circle so it's just an example where having the width could be useful)

So I have two questions:

• is it possible to get the width of the widget
• if so, can you outline how this can be done?

class RoundButton extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Container(
        decoration: BoxDecoration(color: Colors.white),
        child: Container (
            decoration: BoxDecoration(
              border: Border.all(width: 6, color: Colors.green),
              borderRadius: const BorderRadius.all(const Radius.circular(**width**/2)),
              //shape: BoxShape.circle,
            ),

            child: Center (
              child: Text(
              "w="+**width**.toString(),
            ),
          )
        ));
  }
}

Answer 1

Apparently, this can be done without LayoutBuilder using the code below. Note that the two const on the borderRadius line had to be removed

  @override
  Widget build(BuildContext context) {
    RenderBox rb = context.findRenderObject() as RenderBox;
    final Size size = rb?.size ?? Size.zero;
    return Container(
        decoration: BoxDecoration(color: Colors.white),
        child: Container (
            decoration: BoxDecoration(
              border: Border.all(width: 6, color: Colors.green),
              borderRadius: BorderRadius.all(Radius.circular(size.width.toInt()/2)),
              //shape: BoxShape.circle,
            ),

            child: Center (
              child: Text(
              "w="+size.height.toString(),
            ),
          )
        ));
  }