Flutter onPressed Function

Question

Error in onPressed Trying to pass onPressed Function but getting Error.

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

class CircleButton extends StatelessWidget {
  CircleButton({required this.icon, required this.onPressed});
  final IconData icon;
  final Function onPressed;                 [![Error][1]][1]//Here
  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      child: Icon(icon),
      onPressed: onPressed,
      style: ElevatedButton.styleFrom(
        elevation: 6.0,
        primary: Color(0xFF4C4F5E),
        shape: CircleBorder(),
        padding: EdgeInsets.all(15),
      ),);
  }}

Does this answer your question? [The argument type 'Function' can't be assigned to the parameter type 'void Function()?' after null safety](https://stackoverflow.com/questions/64484113/the-argument-type-function-cant-be-assigned-to-the-parameter-type-void-funct) — Md. Yeasin Sheikh, Feb 21 '22 at 15:04

score 7 · Answer 1 · answered Feb 21 '22 at 15:05

The Function type is actually a dynamic Function type.

The ElevatedButton expects a void Function to its onPressed method, which there is actually a type that is a typedef for it: VoidCallback

So, replace your Function onPressed with VoidCallback onPressed.

score 1 · Accepted Answer · answered Feb 21 '22 at 15:08

Change Function to VoidCallback

class CircleButton extends StatelessWidget {
  CircleButton({required this.icon, required this.onPressed});
  final IconData icon;
  final VoidCallback onPressed;   //Change Function to VoidCallback
  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: onPressed,
      child: Icon(icon),
      style: ElevatedButton.styleFrom(
        elevation: 6.0,
        primary: Color(0xFF4C4F5E),
        shape: CircleBorder(),
        padding: EdgeInsets.all(15),
      ),
    );
  }
}

Flutter onPressed Function

2 Answers2