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

I want to achieve to make a drawer with different items on it, so I am creating a separate file for the DrawerItems and the with the constructor, pass the data to the main file. But I get the following error on the onPressed function:

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

class DrawerItem extends StatelessWidget {
    
      final String text;
      final Function onPressed;
    
      const DrawerItem({Key key, this.text, this.onPressed}) : super(key: key);
    
      @override
      Widget build(BuildContext context) {
        return FlatButton(
          child: Text(
            text,
            style: TextStyle(
              fontWeight: FontWeight.w600,
              fontSize: 18.0,
            ),
          ),
          onPressed: onPressed,
        );
      }
    }

Anyone knows why?

Change your code to accept a VoidCallback instead of Function for the onPressed.
By the way VoidCallback is just shorthand for void Function() so you could also define it as final void Function() onPressed;

Updated code:

class DrawerItem extends StatelessWidget {
    
      final String text;
      final VoidCallback onPressed;
    
      const DrawerItem({Key key, this.text, this.onPressed}) : super(key: key);
    
      @override
      Widget build(BuildContext context) {
        return FlatButton(
          child: Text(
            text,
            style: TextStyle(
              fontWeight: FontWeight.w600,
              fontSize: 18.0,
            ),
          ),
          onPressed: onPressed,
        );
      }
    }

Dart 2.12 (Null safety):

Instead of

final Function? onPressed; // Bad

use

final void Function()? onPressed; // Good
final VoidCallback? onPressed; // Good