How to set rounded border to a MaterialButton on Flutter?

Question

I'm trying set rounded border to my MaterialButton, to do it I'm setting a RoundedRectangleBorder to shape attribute's MaterialButton, the problem is that it's not have effect.

Code:

  Widget _showNeedHelpButton() {
    return new Padding(      
      padding: EdgeInsets.fromLTRB(0.0, 5.0, 0.0, 0.0),
      child: new MaterialButton(
        shape: RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(20.0))),
        elevation: 5.0,
        minWidth: 200.0,
        height: 35,
        color: Color(0xFF801E48),
        child: new Text('Preciso de ajuda',
            style: new TextStyle(fontSize: 16.0, color: Colors.white)),
        onPressed: () {
          setState(() {
            _isNeedHelp = true;
          });
        },
      ),
    );
  }

Result:

Answer 1

MaterialButton(
        child: Text('My Button'),
        height: 40,
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(10.0),
        ),
)

RoundedRectangleBorder will help you https://api.flutter.dev/flutter/painting/RoundedRectangleBorder-class.html