How to assign a callback function to a variable-CodePudding

I got this list with some items and each item got a function(MaterialPageRoute). When I print this list in my Screen and wrap it inside a material button ,I want to use the variable onTapAction .

import 'package:admin/constants.dart';
import 'package:flutter/material.dart';

class Raccourcis {
  final String imgSrc, title, onTapAction;

  Raccourcis({this.imgSrc, this.title, this.onTapAction, info});
}

List listeRaccourcis = [
  Raccourcis(
      title: "Ajouter Un Bon de commande",
      imgSrc: "assets/images/commande.png",
      onTapAction:
          "Navigator.push(context,MaterialPageRoute(builder: (context) => const SecondRoute()),);"),

This is how I'm using the list in another Widget :

InkWell(
    onTap: info.onTapAction,
 )

I'm getting the error that : The argument type 'String' can't be assigned to the parameter type 'void Function()'

CodePudding user response：

Your onTapAction parameter in Raccouris class is of type String, it should be of type Function.

class Raccourcis {
  final String imgSrc, title;
  final Function onTapAction;

  Raccourcis({
    required this.imgSrc,
    required this.title,
    required this.onTapAction,
  });
}

class Test extends StatefulWidget {
  const Test({Key? key}) : super(key: key);

  @override
  State<Test> createState() => _TestState();
}

class _TestState extends State<Test> {
  List<Raccourcis> listeRaccourcis = [];
  @override
  void initState() {
    super.initState();
    listeRaccourcis = [
      Raccourcis(
        title: "Ajouter Un Bon de commande",
        imgSrc: "assets/images/commande.png",
        onTapAction: () => Navigator.push(
          context,
          MaterialPageRoute(builder: (context) => ScreenB()),
        ),
      ),
    ];
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Column(
          children: listeRaccourcis
              .map(
                (e) => GestureDetector(
                  onTap: () => e.onTapAction(),
                  child: Text(e.title),
                ),
              )
              .toList(),
        ),
      ),
    );
  }
}

CodePudding user response：

You have put some quotes, so it's a string, and you can't assign a string to a void Function parameter, as the error says.

You shoud do instead:

onTapAction:
      Navigator.push(context,MaterialPageRoute(builder: (context) => const SecondRoute()),);)

CodePudding user response：

The problem is that you are declaring the onTapAction as a String and not as a void() Func. Your onTapAction should look like this

onTapAction: {
         Navigator.push(context,MaterialPageRoute(builder: (context) => const SecondRoute()));
      }

or this

onTapAction: () =>
         Navigator.push(context,MaterialPageRoute(builder: (context) => const SecondRoute()))

Also, you should change your Raccourcis class to:

class Raccourcis {
      final String imgSrc, title;
      final Function() onTapAction;
    
      Raccourcis({this.imgSrc, this.title, required this.onTapAction, info});
}

CodePudding user response：

I would recommend using the VoidCallback and ValueChanged types. They are used in all Flutter UI widgets.

VoidCallback: https://api.flutter.dev/flutter/dart-ui/VoidCallback.html

ValueChanged: https://api.flutter.dev/flutter/foundation/ValueChanged.html