What is the difference between using Align or using Positioned flutter - layout

Question

Her's a concrete example of using both Positionned Widget and Align Widget!
But I had a problem figuring what to use ! though original problem is to set some FABs's Offsets relatively to its Container not to the screen
Stack(
children: <Widget>[
Positioned(left: 0.0, child: Text("Top\nleft")),
Positioned(bottom: 0.0, child: Text("Bottom\nleft")),
Positioned(top: 0.0, right: 0.0, child: Text("Top\nright")),
Positioned(bottom: 0.0, right: 0.0, child: Text("Bottom\nright")),
Positioned(bottom: 0.0, right: 0.0, child: Text("Bottom\nright")),
Positioned(left: width / 2, top: height / 2, child: Text("Center")),
Positioned(top: height / 2, child: Text("Center\nleft")),
Positioned(top: height / 2, right: 0.0, child: Text("Center\nright")),
Positioned(left: width / 2, child: Text("Center\ntop")),
Positioned(left: width / 2, bottom: 0.0, child: Text("Center\nbottom")),
],
)
Example #2 (Using Align in Stack)
Stack(
children: <Widget>[
Align(alignment: Alignment.center, child: Text("Center"),),
Align(alignment: Alignment.topRight, child: Text("Top\nRight"),),
Align(alignment: Alignment.centerRight, child: Text("Center\nRight"),),
Align(alignment: Alignment.bottomRight, child: Text("Bottom\nRight"),),
Align(alignment: Alignment.topLeft, child: Text("Top\nLeft"),),
Align(alignment: Alignment.centerLeft, child: Text("Center\nLeft"),),
Align(alignment: Alignment.bottomLeft, child: Text("Bottom\nLeft"),),
Align(alignment: Alignment.topCenter, child: Text("Top\nCenter"),),
Align(alignment: Alignment.bottomCenter, child: Text("Bottom\nCenter"),),
Align(alignment: Alignment(0.0, 0.5), child: Text("Custom\nPostition", style: TextStyle(color: Colors.red, fontSize: 20.0, fontWeight: FontWeight.w800),),),
],
);
> Blockquot
e

Answer 1

Positioned is an offset based alignment which uses DP as unit
Align use a % of the parent size
As such, Alignment(0.1, 0.1) cannot be represented using a Positioned. And similarly,Align cannot represent a Positioned(top: 10, left: 10).
Secondly, Positioned is on a different flow.
Stack can size itself based on the size of one of its children excluding Positioned widgets.
As such, using an Align vs Positioned can result in Stack taking a different size.

Answer 2

Positioned can only be used within a Stack and positions a child relative to the Stack size.
https://docs.flutter.io/flutter/widgets/Positioned-class.html
Align will be as big as possible within its parent (or a size relative to the children if heightFactor, widthFactor are passed) and positions its child relative to itself. Align can be used everywhere, not only within a Stack.
https://docs.flutter.io/flutter/widgets/Align-class.html

Answer 3

Kind of related but on a slightly different subject,
If anyone comes here looking for a solution to why their widget doesn't precisely align where they put it inside a stack (whether it's Positioned or Align). That is probably caused by some padding value that you're not aware of it's there. Simply, open up dev tools and go through widgets one by one to check if there are any additional spaces.
And on a more rare occasion, if you wrapped one of the top widget tree elements with SafeArea, it also adds padding to both the bottom and the top. It may have been caused by that too. Just a heads up :')