ChangeNotifierProxyProvider4<T, T2, T3, T4, R extends ChangeNotifier?> class
A ChangeNotifierProvider that builds and synchronizes a ChangeNotifier
with external values.
To understand better this variation of ChangeNotifierProvider, we can look into the following code using the original provider:
ChangeNotifierProvider(
create: (context) {
return MyChangeNotifier(
myModel: Provider.of<MyModel>(context, listen: false),
);
},
child: ...
)
In this example, we built a MyChangeNotifier
from a value coming from
another provider: MyModel
.
This works as long as MyModel
never changes. But if it somehow updates,
then our ChangeNotifier
will never update accordingly.
To solve this issue, we could instead use this class, like so:
ChangeNotifierProxyProvider<MyModel, MyChangeNotifier>(
create: (_) => MyChangeNotifier(),
update: (_, myModel, myNotifier) => myNotifier
..update(myModel),
child: ...
);
In that situation, if MyModel
were to update, then MyChangeNotifier
will
be able to update accordingly.
Notice how MyChangeNotifier
doesn't receive MyModel
in its constructor
anymore. It is now passed through a custom setter/method instead.
A typical implementation of such MyChangeNotifier
could be:
class MyChangeNotifier with ChangeNotifier {
void update(MyModel myModel) {
// Do some custom work based on myModel that may call `notifyListeners`
}
}
-
DON'T create the
ChangeNotifier
insideupdate
directly.This will cause your state to be lost when one of the values used updates. It will also cause unnecessary overhead because it will dispose the previous notifier, then subscribes to the new one.
Instead reuse the previous instance, and update some properties or call some methods.
ChangeNotifierProxyProvider<MyModel, MyChangeNotifier>(
// may cause the state to be destroyed involuntarily
update: (_, myModel, myNotifier) => MyChangeNotifier(myModel: myModel),
child: ...
);
-
PREFER using ProxyProvider when possible.
If the created object is only a combination of other objects, without http calls or similar side-effects, then it is likely that an immutable object built using ProxyProvider will work.
- Inheritance
-
- Object
- SingleChildStatelessComponent
- InheritedProvider<
R> - ListenableProxyProvider0<
R> - ListenableProxyProvider4<
T, T2, T3, T4, R> - ChangeNotifierProxyProvider4
Constructors
-
ChangeNotifierProxyProvider4({Key? key, required Create<
R> create, required ProxyProviderBuilder4<T, T2, T3, T4, R> update, bool? lazy, TransitionBuilder? builder, Component? child}) -
Initializes
key
for subclasses.
Properties
- builder → TransitionBuilder?
-
Syntax sugar for obtaining a
BuildContext
that can read the provider created.finalinherited - hashCode → int
-
The hash code for this object.
no setterinherited
- key → Key?
-
Controls how one component replaces another component in the tree.
finalinherited
- runtimeType → Type
-
A representation of the runtime type of the object.
no setterinherited
Methods
-
build(
BuildContext context) → Iterable< Component> -
Describes the part of the user interface represented by this component.
inherited
-
buildWithChild(
BuildContext context, Component? child) → Iterable< Component> -
A build method that receives an extra
child
parameter.inherited -
createElement(
) → _InheritedProviderElement< R> -
Creates a
StatelessElement
to manage this component's location in the tree.inherited -
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