How to initialise a void function in a class-CodePudding

I was creating a new class name RoundedButton which is below

class RoundedButton extends StatelessWidget {
  const RoundedButton({required this.colour, required this.title, required this.onPressed});
  final Color colour;
  final String title;
  final Function onPressed;
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.symmetric(vertical: 16.0),
      child: Material(
        elevation: 5.0,
        color: colour,
        borderRadius: BorderRadius.circular(30.0),
        child: MaterialButton(
          onPressed: onPressed,
          minWidth: 200.0,
          height: 42.0,
          child: Text(
           title,
          ),
        ),
      ),
    );
  }
}

but the onPressed function variable I have created keeps bringing this error every time I use it in the onPressed property of the textfield

The argument type 'Function' can't be assigned to the parameter type 'void Function()?'.

and when I change the onPressed data type to void, it still not working. What have I done wrong in this?

CodePudding user response：

Change the type of onPressed to either VoidCallback or Function().

CodePudding user response：

you can use VoidCallback or void Function()

try this,

class RoundedButton extends StatelessWidget {
  const RoundedButton({
    Key? key,
    required this.colour,
    required this.title,
    required this.onPressed,
  }) : super(key: key);

  final Color colour;
  final VoidCallback onPressed;
  final String title;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.symmetric(vertical: 16.0),
      child: Material(
        elevation: 5.0,
        color: colour,
        borderRadius: BorderRadius.circular(30.0),
        child: MaterialButton(
          onPressed: onPressed,
          minWidth: 200.0,
          height: 42.0,
          child: Text(
            title,
          ),
        ),
      ),
    );
  }
}