ChangeNotifierProvider<T extends ChangeNotifier?> class
Listens to a ChangeNotifier
, expose it to its descendants and rebuilds
dependents whenever ChangeNotifier.notifyListeners
is called.
Depending on whether you want to create or reuse a ChangeNotifier
,
you will want to use different constructors.
Creating a ChangeNotifier
:
To create a value, use the default constructor. Creating the instance
inside build
using ChangeNotifierProvider.value
will lead to memory
leaks and potentially undesired side-effects.
See this stackoverflow answer
which explains in further details why using the .value
constructor to
create values is undesired.
- DO create a new
ChangeNotifier
insidecreate
.
ChangeNotifierProvider(
create: (_) => new MyChangeNotifier(),
child: ...
)
- DON'T use
ChangeNotifierProvider.value
to create yourChangeNotifier
.
ChangeNotifierProvider.value(
value: new MyChangeNotifier(),
child: ...
)
-
DON'T create your
ChangeNotifier
from variables that can change over the time.In such situation, your
ChangeNotifier
would never be updated when the value changes.
int count;
ChangeNotifierProvider(
create: (_) => new MyChangeNotifier(count),
child: ...
)
If you want to pass variables to your ChangeNotifier
, consider using
ChangeNotifierProxyProvider.
Reusing an existing instance of ChangeNotifier
:
If you already have an instance of ChangeNotifier
and want to expose it,
you should use ChangeNotifierProvider.value instead of the default
constructor.
Failing to do so may dispose the ChangeNotifier
when it is still in use.
- DO use ChangeNotifierProvider.value to provide an existing
ChangeNotifier
.
MyChangeNotifier variable;
ChangeNotifierProvider.value(
value: variable,
child: ...
)
- DON'T reuse an existing
ChangeNotifier
using the default constructor
MyChangeNotifier variable;
ChangeNotifierProvider(
create: (_) => variable,
child: ...
)
See also:
ChangeNotifier
, which is listened by ChangeNotifierProvider.- ChangeNotifierProxyProvider, to create and provide a
ChangeNotifier
of variables from other providers. - ListenableProvider, similar to ChangeNotifierProvider but works with
any
Listenable
.
- Inheritance
-
- Object
- SingleChildStatelessComponent
- InheritedProvider<
T> - ListenableProvider<
T> - ChangeNotifierProvider
Constructors
-
ChangeNotifierProvider({Key? key, required Create<
T> create, bool? lazy, TransitionBuilder? builder, Component? child}) -
Creates a
ChangeNotifier
usingcreate
and automatically disposes it when ChangeNotifierProvider is removed from the component tree. - ChangeNotifierProvider.value({Key? key, required T value, TransitionBuilder? builder, Component? child})
-
Provides an existing
ChangeNotifier
.
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< T> -
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