失败的断言：第 551 行 pos 12：“child.hasSize”：不正确

Question

I'm new in Flutter, I'm working on an e-commerce website, I want to add a Grid in my welcome page showing recent products, I'm trying to use GridVeiw.builder, but I got an error

Failed assertion: line 551 pos 12: 'child.hasSize': is not true.

I don't understand why I'm seeing this error.

My Welcome Screen

import 'package:ecommerce_practice/components/carousel.dart';
import 'package:ecommerce_practice/components/horizontal_list.dart';
import 'package:ecommerce_practice/components/products.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

class WelcomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('E-commerce'),
        backgroundColor: Colors.red,
        actions: [
          IconButton(
            icon: Icon(
              Icons.search,
            ),
            color: Colors.white,
            onPressed: () {},
          ),
          IconButton(
            icon: Icon(Icons.shopping_cart),
            color: Colors.white,
            onPressed: () {},
          )
        ],
      ),
      drawer: Drawer(
        child: ListView(
          children: [
            UserAccountsDrawerHeader(
              accountName: Text("Aleem"),
              accountEmail: Text('aleem.alam@outlook.com'),
              currentAccountPicture: GestureDetector(
                child: CircleAvatar(
                  backgroundColor: Colors.grey,
                  child: Icon(
                    Icons.person,
                    color: Colors.white,
                  ),
                ),
              ),
              decoration: BoxDecoration(color: Colors.red),
            ),
            DrawerMenuButton(
              title: 'Home',
              icon: Icon(
                Icons.home,
                color: Colors.red,
              ),
            ),
            DrawerMenuButton(
              title: 'My Account',
              icon: Icon(
                Icons.person,
                color: Colors.red,
              ),
            ),
            DrawerMenuButton(
              title: 'My Order',
              icon: Icon(
                Icons.shopping_basket,
                color: Colors.red,
              ),
            ),
            DrawerMenuButton(
              title: 'Category',
              icon: Icon(
                Icons.category,
                color: Colors.red,
              ),
            ),
            DrawerMenuButton(
              title: 'Favourites',
              icon: Icon(
                Icons.favorite,
                color: Colors.red,
              ),
            ),
            Divider(),
            DrawerMenuButton(
              title: 'Settings',
              icon: Icon(
                Icons.settings,
                color: Colors.blue,
              ),
            ),
            DrawerMenuButton(
              title: 'About Us',
              icon: Icon(
                Icons.help,
                color: Colors.blue,
              ),
            ),
          ],
        ),
      ),
      body: ListView(
        children: [
          ImageCarousel(),
          Padding(
            padding: EdgeInsets.all(10.0),
            child: Text('Category'),
          ),
          HorizontalList(),
          Padding(
            padding: EdgeInsets.all(10.0),
            child: Text('Recent Product'),
          ),
          Products(),
        ],
      ),
    );
  }
}

class DrawerMenuButton extends StatelessWidget {
  DrawerMenuButton({this.title, this.icon});
  final String title;
  final Icon icon;
  @override
  Widget build(BuildContext context) {
    return InkWell(
      onTap: () {},
      child: ListTile(
        title: Text(title),
        leading: icon,
      ),
    );
  }
}

products.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

class Products extends StatefulWidget {
  @override
  _ProductsState createState() => _ProductsState();
}

class _ProductsState extends State<Products> {
  List<dynamic> products = [
    {
      'name': 'Shirt',
      'image': 'images/category.jpg',
      'old_price': 200,
      'price': 140,
    },
    {
      'name': 'Shirt',
      'image': 'images/category.jpg',
      'old_price': 200,
      'price': 140,
    }
  ];
  @override
  Widget build(BuildContext context) {
    return GridView.builder(
      itemCount: products.length,
      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: 2,
      ),
      itemBuilder: (context, index) {
        return Product(
          name: products[index]['name'],
          image: products[index]['image'],
          oldPrice: products[index]['old_price'],
          finalPrice: products[index]['price'],
        );
      },
    );
  }
}

class Product extends StatelessWidget {
  Product({this.name, this.image, this.oldPrice, this.finalPrice});
  final String name, image;
  final int oldPrice, finalPrice;
  @override
  Widget build(BuildContext context) {
    return Card(
      child: Hero(
        tag: name,
        child: Material(
          child: InkWell(
            onTap: () {},
            child: GridTile(
              footer: Container(
                color: Colors.white,
                child: ListTile(
                  leading: Text(
                    name,
                    style: TextStyle(
                      fontWeight: FontWeight.bold,
                    ),
                  ),
                ),
              ),
              child: Image.asset(
                image,
                fit: BoxFit.cover,
              ),
            ),
          ),
        ),
      ),
    );
  }
}

Answer 1

Try setting the shrinkWrap property of the GridView to true so it takes only the space needed based on it's items:

I added a demo using your code as an example:

 return GridView.builder(
    itemCount: products.length,
    shrinkWrap: true, // new line
    physics: NeverScrollableScrollPhysics(), // new line
    gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
      crossAxisCount: 2,
    ),
    itemBuilder: (context, index) {
      return Product(
        name: products[index]['name'],
        image: products[index]['image'],
        oldPrice: products[index]['old_price'],
        finalPrice: products[index]['price'],
      );
    },
  );

---

EDIT: To prevent the GridView from scrolling separately in your ListView , set the physics of the GridView to NeverScrollablePhysics .