Anchor floating action button to Card - dart

Question

When creating a Card (for example using the code from the Docs) , how can I anchor a FAB to the Card (the green circle in the image below), like in this question for Android.
I saw a similar question for attaching a FAB to the AppBar, but the solution relies on the AppBar being a fixed height. When using a Card, the height isn't fixed ahead of time so the same solution can't be used.

Answer 1

You can place the FloatingActionButton in an Align widget and play with the heightFactor property.
For example:
class MyCard extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Card(
child: Column(
children: <Widget>[
SizedBox(height: 100.0, width: double.infinity),
Align(
alignment: Alignment(0.8, -1.0),
heightFactor: 0.5,
child: FloatingActionButton(
onPressed: null,
child: Icon(Icons.add),
),
)
],
),
);
}
}

Answer 2

Correct solution for anchor FAB.
Another solution using stack and container. FAB's place is based on its sibling Container widget's size and clicks/taps work properly.
import 'package:flutter/material.dart';
void main() {
runApp(
MaterialApp(
home: MyWidget(),
),
);
}
class MyWidget extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Stack(
children: <Widget>[
Container(
padding: EdgeInsets.only(bottom: 28),
child: Container(
width: double.infinity,
height: 150,
color: Color.fromRGBO(55, 55, 55, 0.2),
padding: EdgeInsets.all(15),
child: Text(
'Any container with bottom padding with half size of the FAB'),
),
),
Positioned(
bottom: 0,
right: 10,
child: FloatingActionButton(
child: Icon(
Icons.play_arrow,
size: 40,
),
onPressed: () => print('Button pressed!'),
),
),
],
),
);
}
}
CodePan link for anchor FAB

Answer 3

The correct solution is to use a "Stack" and "Positioned" widged like:
return Stack(
children: <Widget>[
Card(
color: Color(0xFF1D3241),
margin: EdgeInsets.only(bottom: 40), // margin bottom to allow place the button
child: Column(children: <Widget>[
...
],
),
Positioned(
bottom: 0,
right: 17,
width: 80,
height: 80,
child: FloatingActionButton(
backgroundColor: Color(0xFFF2638E),
child: Icon(Icons.play_arrow,size: 70,)
),
),
],
);