Currently I am coding a shop application and trying to make the product card clickable, however there was an error that occurred:

Exception caught by gesture library, type 'Null' is not a subtype of type 'String' of 'function result'

Here is my code for the product card (button):

import 'package:flutter/material.dart';
import 'package:flutter_svg/flutter_svg.dart';
import 'package:minimlst/components/product_card.dart';
import 'package:minimlst/constants.dart';
import 'package:minimlst/models/product.dart';
import 'package:minimlst/screens/details/details_screen.dart';
import 'package:minimlst/screens/home/components/discount_banner.dart';
import 'package:minimlst/screens/home/components/home_header.dart';
import 'package:minimlst/size_config.dart';

class Body extends StatelessWidget {
  const Body({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: SingleChildScrollView(
        child: Column(
          children: [
            SizedBox(height: getProportionateScreenWidth(20)),
            HomeHeader(),
            SizedBox(height: getProportionateScreenWidth(30)),
            DiscountBanner(),
            SizedBox(height: getProportionateScreenWidth(20)),
            Column(children: [
              Text(
                "Our Catalog",
                style: TextStyle(
                  fontSize: 18,
                  fontWeight: FontWeight.bold,
                  color: Colors.black,
                ),
              ),
            ]),
            SizedBox(height: getProportionateScreenWidth(30)),
            SingleChildScrollView(
              scrollDirection: Axis.vertical,
              child: Column(
                children: [
                  ...List.generate(
                    demoProducts.length,
                    (index) => ProductCard(
                        product: demoProducts[index],
                        press: () => Navigator.pushNamed(
                            context, DetailsScreen.routeName)),
                  ),
                  SizedBox(width: getProportionateScreenWidth(20)),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

and here is my code for the ProductCard:

import 'package:flutter/material.dart';
import 'package:minimlst/models/product.dart';

import '../constants.dart';
import '../size_config.dart';

class ProductCard extends StatelessWidget {
  const ProductCard({
    Key? key,
    this.width = 140,
    this.aspectRetio = 1.02,
    required this.product,
    required this.press,
  }) : super(key: key);

  final double width, aspectRetio;
  final Product product;
  final GestureTapCallback press;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: press,
      child: SizedBox(
        width: getProportionateScreenWidth(width),
        child: Padding(
          padding: EdgeInsets.only(left: getProportionateScreenWidth(20)),
          child: Column(
            children: [
              AspectRatio(
                aspectRatio: aspectRetio,
                child: Container(
                    padding: EdgeInsets.all(getProportionateScreenWidth(20)),
                    decoration: BoxDecoration(
                      color: kSecondaryColor.withOpacity(0.2),
                      borderRadius: BorderRadius.circular(15),
                    ),
                    child: Image.asset(product.images[0])),
              ),
              Text(
                product.title,
                style: TextStyle(color: Colors.black),
                maxLines: 2,
              ),
              Row(
                children: [
                  Text(
                    "\$${product.price}",
                    style: TextStyle(
                      fontSize: getProportionateScreenWidth(18),
                      fontWeight: FontWeight.w600,
                      color: kPrimaryColor,
                    ),
                  ),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }
}

Please help if you can, any kind of help would be very much appreciated, if you need any other bits of the code lmk

CodePudding user response：

the issue is that you are passing wrong function argument to press
As syntax is () => Navigator.pushNamed(
                            context, DetailsScreen.routeName)
   as fat arrow refers return so you are returning Navigator.pushNamed as argument required function who's return type must be void etc

so the change is press:(){
Navigator.pushNamed(context, DetailsScreen.routeName)
}