I want use provider
(ChangeNotifierProvider
) and ChangeNotifier
for manage app state. But how I can access state from one model in another model?
Use case: In chat app, one model for store user information. Other model use user information (for example user id) to make call to database (Firestore) and get stream of chat data.
For example:
class Model1 extends ChangeNotifier {
final List<Item> items = [];
class Model2 extends ChangeNotifier {
//Access items from Model1 here
items;
Is this possible? I not like have very big Model because is hard to maintain.
Thanks!
Can I obtain two different providers using the same type? No. While you can have multiple providers sharing the same type, a widget will be able to obtain only one of them: the closest ancestor.
If you want to pass the value to another model, which value should be passed? From my understanding, you just need to assign the value from the property " greencar " of the class " carone " to the property " redcar " of the class " cartwo ".
Because we can pass data between screens without the latest Provider package, ChangeNotifierProvider, and ChangeNotifier. Let’s consider a simple data model where we have a Book class and a list of dummy data based on that Book class constructors.
Because we pass data between classes through class constructor. The following code snippet handles that passage of data. itemBuilder: (ctx, i) => BookItem ( books [i].id, books [i].title, books [i].imageUrl, ), Now we can have a Book Item controller, where we can request that data through class constructor.
For passing data among siblings, there are multiple methods we can choose from as shown below: 1 Combination of the above two methods (callback and use of props). 2 Using Redux. 3 ContextAPI More ...
Using provider
, one model doesn't access another model.
Instead, you should use ProxyProvider
, to combine a model from others.
Your models would look like:
class Foo with ChangeNotifier {
int count = 0;
void increment() {
count++;
notifyListeners();
}
}
class Bar with ChangeNotifier {
int _count;
int get count => _count;
set count(int value) {
if (value != count) {
_count = value;
notifyListeners();
}
}
}
And then you can use ChangeNotifierProxyProvider
this way (assuming there's a `ChangeNotifierProvider higher in your widget tree):
ChangeNotifierProxyProvider<Foo, Bar>(
initialBuilder: (_) => Bar(),
builder: (_, foo, bar) => bar
..count = foo.count, // Don't pass `Foo` directly but `foo.count` instead
)
From v4 the ChangeNotifierProxyProvider
the provider can be constructed like so:
ChangeNotifierProxyProvider<Foo, Bar>(
create: (_) => Bar(),
update: (_, foo, bar) => bar
..count = foo.count,
)
Notice that initialBuilder:
has changed to create:
and
builder:
to update:
Here i given a simple example
main.dart
ChangeNotifierProxyProvider<AuthProvider, ProductsProvider>(
create: (context) => ProductsProvider(),
update: (context, auth, previousProducts) => previousProducts
..update(auth.token, previousProducts.items == null ? [] : previousProducts.items),
),
authProvider.dart
class AuthProvider with ChangeNotifier {
String _token;
// _token is a response token.
String get token {
return _token;
}
productsProvider.dart
Product is a class of single product
class ProductsProvider with ChangeNotifier {
List<Product> _items = [];
String _authToken;
void update(authToken, items) {
_items = items;
_authToken = authToken;
notifyListeners();
}
}
Product.dart
class Product with ChangeNotifier {
final String id;
final String title;
final String description;
final double price;
final String imageUrl;
bool isFavorite;
Product({
@required this.id,
@required this.title,
@required this.description,
@required this.price,
@required this.imageUrl,
this.isFavorite = false,
});
}
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With