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samples/provider_shopper/lib/screens/catalog.dart

128 lines
3.8 KiB

// Copyright 2019 The Flutter team. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:provider_shopper/models/cart.dart';
import 'package:provider_shopper/models/catalog.dart';
class MyCatalog extends StatelessWidget {
const MyCatalog({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return Scaffold(
body: CustomScrollView(
slivers: [
_MyAppBar(),
const SliverToBoxAdapter(child: SizedBox(height: 12)),
SliverList(
delegate: SliverChildBuilderDelegate(
(context, index) => _MyListItem(index)),
),
],
),
);
}
}
class _AddButton extends StatelessWidget {
final Item item;
const _AddButton({required this.item, Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
// The context.select() method will let you listen to changes to
// a *part* of a model. You define a function that "selects" (i.e. returns)
// the part you're interested in, and the provider package will not rebuild
// this widget unless that particular part of the model changes.
//
// This can lead to significant performance improvements.
var isInCart = context.select<CartModel, bool>(
// Here, we are only interested whether [item] is inside the cart.
(cart) => cart.items.contains(item),
);
return TextButton(
onPressed: isInCart
? null
: () {
// If the item is not in cart, we let the user add it.
// We are using context.read() here because the callback
// is executed whenever the user taps the button. In other
// words, it is executed outside the build method.
var cart = context.read<CartModel>();
cart.add(item);
},
style: ButtonStyle(
overlayColor: MaterialStateProperty.resolveWith<Color?>((states) {
if (states.contains(MaterialState.pressed)) {
return Theme.of(context).primaryColor;
}
return null; // Defer to the widget's default.
}),
),
child: isInCart
? const Icon(Icons.check, semanticLabel: 'ADDED')
: const Text('ADD'),
);
}
}
class _MyAppBar extends StatelessWidget {
@override
Widget build(BuildContext context) {
return SliverAppBar(
title: Text('Catalog', style: Theme.of(context).textTheme.headline1),
floating: true,
actions: [
IconButton(
icon: const Icon(Icons.shopping_cart),
onPressed: () => Navigator.pushNamed(context, '/cart'),
),
],
);
}
}
class _MyListItem extends StatelessWidget {
final int index;
const _MyListItem(this.index, {Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
var item = context.select<CatalogModel, Item>(
// Here, we are only interested in the item at [index]. We don't care
// about any other change.
(catalog) => catalog.getByPosition(index),
);
var textTheme = Theme.of(context).textTheme.headline6;
return Padding(
padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
child: LimitedBox(
maxHeight: 48,
child: Row(
children: [
AspectRatio(
aspectRatio: 1,
child: Container(
color: item.color,
),
),
const SizedBox(width: 24),
Expanded(
child: Text(item.name, style: textTheme),
),
const SizedBox(width: 24),
_AddButton(item: item),
],
),
),
);
}
}