How can I assign an argument of type 'Function' to a parameter of type 'void Function()'?

Question

I'm trying to create a stateless widget like this:

import 'package:flutter/material.dart';

class Answers extends StatelessWidget {
  final Function nextQuestion;

  Answers(this.nextQuestion);

  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: nextQuestion,
      child: Text("Answer"),    
    );
  }
}

However, an error appears in the onPressed argument: "The argument type 'Function' can't be assigned to the parameter type 'void Function()?'". How can I solve it?

Does this answer your question? [error: The argument type 'Future' can't be assigned to the parameter type 'void Function()'](https://stackoverflow.com/questions/57761489/error-the-argument-type-future-cant-be-assigned-to-the-parameter-type-void) — padaleiana, Jun 27 '21 at 16:15

score 7 · Answer 1 · answered Jun 26 '21 at 16:16

7

Just change the type of nextQuestion to void Function():

final void Function() nextQuestion;

answered Jun 26 '21 at 16:16

enzo

9,861
3
15
38

score 0 · Answer 2 · answered Nov 03 '21 at 10:46

0

changing

  final Function nextQuestion;

to

final VoidCallback nextQuestion;

This solved my issue.

answered Nov 03 '21 at 10:46

Shishir Rijal

133
1
5

score 0 · Answer 3 · answered Dec 20 '21 at 02:47

Change type of nextQuestion to VoidCallback which can be used if you have a function which returning no data with no arguments. change your datatype from Function to VoidCallback.

final VoidCallback nextQuestion;

       or you can put anonymous function in front of onPressed (){}

onPressed: ()=>nextQuestion,

How can I assign an argument of type 'Function' to a parameter of type 'void Function()'?

3 Answers3