HelpProvider class

Help with Provider State Management

ChangeNotifier
  • Provides change notification to listeners/subscribers
    • via notifyListeners()
    • causes rebuild
  • e.g.,
class ShoppingCartModel extends ChangeNotifier {
  final List<Item> items = [];
  void addToCart(Item item) {
    items.add(item);
    notifyListeners();
  }
}
ChangeNotifierProvider
  • Provides instance of ChangeNotifier to descendants
    • should not place higher than necessary to prevent pollution of scope
  • e.g.,
void main() {
  ChangeNotifierProvider(
    create: (context) => ShoppingCartModel(),
    child: constMyApp,
  )
}
  • Multiple providers possible:
void main() {
  runApp(
    MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (context) => CartModel()),
        Provider(create: (context) => SomeOtherClass()),
      ],
      child: const MyApp(),
    ),
  );
}
Consumer
  • Grants access to provider state and triggers rebuild when provider state changes
    • type of model must be specified, e.g., <CartModel>
    • put Consumer as deep in tree as possible to prevent unnecessary rebuilds
  • e.g.,
return Consumer<CartModel>(
  builder: (context, cart, child) {
    return Text("Total price: ${cart.totalPrice}");
  },
);
  • arguments:
    • context
    • ChangeNotifier instance
      • Instance of requested provider type
    • child
      • Used for optimisation
        • when there are expensive widgets that
          • is under Consumer, and
          • does not change with ChangeNotifier
          • e.g.,
return Consumer<CartModel>(
  builder: (context, cart, child) => Stack(
    children: [
      /// Use SomeExpensiveWidget here, without rebuilding every time.
      if (child != null) child,
      Text("Total price: ${cart.totalPrice}"),
    ],
  ),
  /// Build the expensive widget here.
  child: const SomeExpensiveWidget(),
);
Provider.of
  • Grants access to provider state without rebuild
Provider.of<CartModel>(context, listen: false).removeAll();

Constructors

HelpProvider()

Properties

hashCode → int
The hash code for this object.
no setterinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
toString() → String
A string representation of this object.
inherited

Operators

operator ==(Object other) → bool
The equality operator.
inherited