Flutter/Dart - Difference between () {} and () => {}

Question

In Flutter/Dart the examples sometimes show fat arrow and sometimes dont. Here are examples:

RaisedButton(
  onPressed: () {
    setState(() {
      _myTxt = \"         


        

Answer 1

They are both for expressing anonymous functions. The fat arrow is for returning a single line, braces are for returning a code block.

A fat arrow trying to return a code block will not compile.