[flutter-05] Center

1. Center

• 居中组件: 相对于整个屏幕的居中

Widget build(BuildContext context) {
    return Center(
      child: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Checkbox(
            value: true,
            onChanged: (value) {
              print('click- checkbox: $value');
            },
          ),
          Text(
            '勾选协议',
            style: TextStyle(fontSize: 36),
            textDirection: TextDirection.ltr,
          ),
        ],
      ),
    );
  }