CODEWITHSUNDEEP
flutterandroid-studiodart
jonnyf
jonnyf

Reputation: 21

Function in flutter

I try to use a function in a widget but i recive this error Error: The argument type 'Function' can't be assigned to the parameter type 'void Function()?'.

I search here and see that someone suggest to use the same metod that I set in my code so what's the problem?

import 'package:flutter/material.dart';

class ReusableCard extends StatelessWidget {
  ReusableCard(
      {required this.colour, required this.cardChild, required this.onPress});
  final Color colour;
  final Widget cardChild;
  final Function onPress;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: onPress,
      child: Container(
        child: cardChild,
        margin: EdgeInsets.all(15.0),
        decoration: BoxDecoration(
          borderRadius: BorderRadius.circular(10.0),
          color: colour,
        ),
      ),
    );
  }
}

Upvotes: 0

Views: 889

Answers (4)

venir
venir

Reputation: 2087

By default, the Function type is a dynamic-type-value-returning Function with no parameters.

Typically, Flutter expects void callbacks inside its buttons, which means it expects a void Function type, with no arguments.

A common, flexible and readable way to work around this is to wrap your function with a void function, like:

() => myFunction()

This would work even if your function is very different (e.g. it has some arguments), making your code more flexible.

() => myFunctionThatAcceptsAnInteger(5)

Upvotes: 1

Eugene Kuzmenko
Eugene Kuzmenko

Reputation: 1487

In Flutter we already have the signature of callbacks that have no arguments and return no data - VoidCallback.

You can use it:

final VoidCallback onPress;

Also, we have ValueSetter<T>, ValueGetter<T>, and others. foundation-library

Upvotes: 1

Dorrin-sot
Dorrin-sot

Reputation: 331

Replace onTap: onPress with onTap: () => onPress()

Upvotes: 1

Chalwe19
Chalwe19

Reputation: 582

change final Function onPress; to final Function() onPress;

Upvotes: 1

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