Flutter set widget position exactly center of the screen

Question

I want to put a container widget in the middle of the device screen. However, since I used the SizedBox() and SvgPicture.asset() widgets before that, the container does not come right in the middle of the device. How can I do this?

This is my code:

class CenterWidget extends StatefulWidget {
  const CenterWidget({Key? key}) : super(key: key);

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

class _CenterWidgetState extends State<CenterWidget> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 30),
          child: Column(
            mainAxisAlignment: MainAxisAlignment.start,
            crossAxisAlignment: CrossAxisAlignment.start,
            mainAxisSize: MainAxisSize.max,
            children: [
              const SizedBox(height: 56),
              SvgPicture.asset(ImageConstants.instance.logoSvg,
                  width: (MediaQuery.of(context).size.width - 60) / 2),
              Expanded(
                child: Center(
                  child: Container(
                    color: Colors.red,
                    width: 100,
                    height: 100,
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

Answer 1

Use a top center aligned stack, and put the widget you want to be centered within a Positioned.fill widget. You can put the spacer and logo in their own column to keep them arranged vertically:

class _CenterWidgetState extends State<CenterWidget> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 30),
          child: Stack(
            alignment: Alignment.topCenter,
            children: [
              Column(
                children: [
                  const SizedBox(height: 56),
                  SvgPicture.asset(ImageConstants.instance.logoSvg,
                      width: (MediaQuery.of(context).size.width - 60) / 2),
                ],
              ),
              Positioned.fill(
                child: Center(
                  child: Container(
                    color: Colors.red,
                    width: 100,
                    height: 100,
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}