Flutter - center button - flutter

Question

I'm creating a UI with 5 buttons. One of them should be center and its width should be 50% of the screen. The height should be the same size (it should be a circle). I tried with MediaQuery.of(context).size.width but it doesn't work.
This is the closest I got:
The code is:
Widget _playButton() {
return FractionallySizedBox(
widthFactor: 0.5,
heightFactor: 0.5, // I know this is wrong
child: Container(
alignment: new FractionalOffset(0.0, 0.0),
color: Colors.red,
/*decoration: new BoxDecoration(
color: hexToColor('#E8532E'),
shape: BoxShape.circle,
),*/
child: Center(
child: Text(
"PLAY",
style: TextStyle(fontSize: 20.0, color: Colors.white),
),
),
),
);
}
The container where I have this button:
Widget build(BuildContext context) {
return new MaterialApp(
debugShowCheckedModeBanner: false,
home: new Scaffold(
body: new Stack(
alignment: AlignmentDirectional.center,
children: <Widget>[_myScreenOptions(), _playButton()],
),
),
);
}
Obviously, the rest of the buttons should be clickable.

Answer 1

If you wanna create a circular button, you don't have to worry about width & height, giving only one size is enough... or you can use FractionallySizedBox, as you already did.
Code output:
Sample code:
import 'package:flutter/material.dart';
class SampleCenterButton extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Container(
width: double.infinity,
height: double.infinity,
child: Stack(
alignment: Alignment.center,
children: <Widget>[
_myScreenOptions(),
_playButton(),
],
),
),
);
}
_playButton() {
return GestureDetector(
onTap: () {
print("Play game");
},
child: FractionallySizedBox(
widthFactor: 0.5,
child: Container(
// defining one dimension works as well, as Flutter knows how to render a circle.
// width: MediaQuery.of(context).size.width/2,
decoration: BoxDecoration(
color: Colors.red,
shape: BoxShape.circle,
),
child: Center(
child: Text(
"PLAY",
style: TextStyle(fontSize: 30, color: Colors.white),
),
),
),
),
);
}
_myScreenOptions() {
return Column(
children: <Widget>[
buildRow([
buildOption(Color(0xff1D4554), Icons.person, "Teams"),
buildOption(Color(0xff229B8D), Icons.folder_open, "Pets"),
]),
buildRow([
buildOption(Color(0xffE7C16A), Icons.videogame_asset, "Modes"),
buildOption(Color(0xffF2A061), Icons.settings, "Options"),
]),
],
);
}
Widget buildOption(Color bgColor, IconData iconData, String title) {
return Expanded(
child: Container(
color: bgColor,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Icon(
iconData,
size: 80,
),
Text(
title,
style: TextStyle(fontSize: 30),
),
],
),
),
);
}
buildRow(List<Widget> buttons) {
return Expanded(
child: Row(
mainAxisSize: MainAxisSize.max,
crossAxisAlignment: CrossAxisAlignment.start,
children: buttons,
),
);
}
}