Starter/samples
1
0
Fork 0
mirror of https://github.com/flutter/samples.git synced 2025-11-08 13:58:47 +00:00
Code Issues Releases Wiki Activity

Follow best practice of ProxyProvider updating (#298)

Browse Source 
* Upgrade to pkg:provider 4.0

* Follow best practice of ProxyProvider updating

The addresses feedback from https://github.com/flutter/samples/issues/245. Instead of constructing a new `CartModel`, we merely update the `catalog` field.

We no longer need a fancy constructor, and `CartModel._catalog` cannot be final any more.
This commit is contained in:
Filip Hracek
2020-01-31 13:25:14 -08:00
committed by GitHub
parent 2fae307721
commit c121b2d2a6
4 changed files with 30 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
provider_shopper/lib/main.dart
View File

@@ -27,9 +27,11 @@ class MyApp extends StatelessWidget {
// of ChangeNotifierProvider. Moreover, CartModel depends
// on CatalogModel, so a ProxyProvider is needed.
ChangeNotifierProxyProvider<CatalogModel, CartModel>(
create: (context) => CartModel.empty(),
update: (context, catalog, previousCart) =>
CartModel(catalog, previousCart),
create: (context) => CartModel(),
update: (context, catalog, cart) {
cart.catalog = catalog;
return cart;
},
),
],
child: MaterialApp(

30
provider_shopper/lib/models/cart.dart
View File

@@ -6,25 +6,25 @@ import 'package:flutter/foundation.dart';
import 'package:provider_shopper/models/catalog.dart';
class CartModel extends ChangeNotifier {
/// The current catalog. Used to construct items from numeric ids.
final CatalogModel _catalog;
/// The private field backing [catalog].
CatalogModel _catalog;
/// Internal, private state of the cart. Stores the ids of each item.
final List<int> _itemIds;
final List<int> _itemIds = [];
/// Construct a CartModel instance that is backed by a [CatalogModel] and
/// an optional previous state of the cart.
///
/// If [previous] is not `null`, its items are copied to the newly
/// constructed instance.
CartModel(this._catalog, CartModel previous)
: assert(_catalog != null),
_itemIds = previous?._itemIds ?? [];
/// The current catalog. Used to construct items from numeric ids.
CatalogModel get catalog => _catalog;
/// An empty cart with no Catalog.
CartModel.empty()
: _catalog = null,
_itemIds = [];
set catalog(CatalogModel newCatalog) {
assert(newCatalog != null);
assert(_itemIds.every((id) => newCatalog.getById(id) != null),
'The catalog $newCatalog does not have one of $_itemIds in it.');
_catalog = newCatalog;
// Notify listeners, in case the new catalog provides information
// different from the previous one. For example, availability of an item
// might have changed.
notifyListeners();
}
/// List of items in the cart.
List<Item> get items => _itemIds.map((id) => _catalog.getById(id)).toList();