以下方法怎么可能使用为构造函数保留的“语法糖”？

Question

To illustrate my point, the following code contains a method called ColorValueChanger uses this.passedIn as an optional parameter. I thought this was reserved for constructors?

class Foo extends StatefulWidget {
 final String passedIn;
 // Value passed in from its host
 ColorValueChanger({Key key, this.passedIn}) : super(key: key);
 _FooState createState() => new _FooState();
}
class _FooState extends State<Foo> {
 @override
 Widget build(BuildContext context) {
 return Text(widget.passedIn,);
 }
}

Answer 1

It is a constructor. It sounds more like there is a typo in the example.

The fixed code would be:

class Foo extends StatefulWidget {
 final String passedIn;
 // Value passed in from its host
 Foo({Key key, this.passedIn}) : super(key: key);
 _FooState createState() => new _FooState();
}
class _FooState extends State<Foo> {
 @override
 Widget build(BuildContext context) {
 return Text(widget.passedIn,);
 }
}