Answers for "flutter columns and rows"

flutter center row

mainAxisAlignment: MainAxisAlignment.center //Center Column contents vertically,

next row column in flutter

var phoneNumber = new Row(
  mainAxisSize: MainAxisSize.min,
  children: <Widget>[
    Expanded(
      child: new Padding(
        padding: const EdgeInsets.all(20.0),
        child: countryCodePicker,
      ),
    ),
    Expanded(
      child: new Padding(
        padding: const EdgeInsets.all(20.0),
        child: mobileNumber,
      ),
    ),
  ],
);