(flutter) How can I get argument in class?

Question

I'm new to flutter, and I heard that creating widgets as classes is better. So I'm trying to change functions to classes.

Widget Head(Size size){
  return Container(
    height: size.height*0.3 + 100,
    decoration: BoxDecoration(
        gradient: LinearGradient(
            begin: Alignment.topCenter,
            end: Alignment.bottomCenter,
            colors: [
              Color(0xff3D1472),
              Color(0xff771887),
            ]
        )
    ),
  );
}

the code above is one of the functions I want to change to stateless class. And I tried like this,

class Head extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    
    return Container(
      height: size.height*0.3 + 100,
      decoration: BoxDecoration(
          gradient: LinearGradient(
              begin: Alignment.topCenter,
              end: Alignment.bottomCenter,
              colors: [
                Color(0xff3D1472),
                Color(0xff771887),
              ]
          )
      ),
    );
  }
}

But I still don't know where I should get that 'size'. How can I do that? Thank you for reading, and I'll wait for your advice!

Answer 1

You need to pass the arguments in the constructor, for example:

class Head extends StatelessWidget {
  Head({this.size});

  final int size;

  @override
  Widget build(BuildContext context) {
    
    return Container(
      height: size.height*0.3 + 100,
      decoration: BoxDecoration(
          gradient: LinearGradient(
              begin: Alignment.topCenter,
              end: Alignment.bottomCenter,
              colors: [
                Color(0xff3D1472),
                Color(0xff771887),
              ]
          )
      ),
    );
  }
}

And then when you call it, you can do:

Head(size : 1)