ChangeNotifierProvider<T extends ChangeNotifier> class
Listens to a ChangeNotifier
, expose it to its descendants and rebuilds
dependents whenever ChangeNotifier.notifyListeners
is called.
Depending on wether 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
- SingleChildStatelessWidget
- InheritedProvider<
T> - ListenableProvider<
T> - ChangeNotifierProvider
Constructors
-
ChangeNotifierProvider({Key key, @required Create<
T> create, bool lazy, TransitionBuilder builder, Widget child}) -
Creates a
ChangeNotifier
usingcreate
and automatically dispose it when ChangeNotifierProvider is removed from the widget tree. [...] - ChangeNotifierProvider.value({Key key, @required T value, TransitionBuilder builder, Widget child})
-
Provides an existing
ChangeNotifier
.
Properties
- builder → TransitionBuilder
-
Syntax sugar for obtaining a
BuildContext
that can read the provider created. [...]final, inherited - hashCode → int
-
The hash code for this object. [...]
@nonVirtual, read-only, inherited
- key → Key
-
Controls how one widget replaces another widget in the tree. [...]
final, inherited
- runtimeType → Type
-
A representation of the runtime type of the object.
read-only, inherited
Methods
-
build(
BuildContext context) → Widget -
Describes the part of the user interface represented by this widget. [...]
inherited
-
buildWithChild(
BuildContext context, Widget child) → Widget -
A build method that receives an extra
child
parameter. [...]inherited -
createElement(
) → _InheritedProviderElement< T> -
Creates a
StatelessElement
to manage this widget's location in the tree. [...]inherited -
debugDescribeChildren(
) → List< DiagnosticsNode> -
Returns a list of
DiagnosticsNode
objects describing this node's children. [...]@protected, inherited -
debugFillProperties(
DiagnosticPropertiesBuilder properties) → void -
Add additional properties associated with the node. [...]
inherited
-
noSuchMethod(
Invocation invocation) → dynamic -
Invoked when a non-existent method or property is accessed. [...]
inherited
-
toDiagnosticsNode(
{String name, DiagnosticsTreeStyle style}) → DiagnosticsNode -
Returns a debug representation of the object that is used by debugging
tools and by
DiagnosticsNode.toStringDeep
. [...]inherited -
toString(
{DiagnosticLevel minLevel = DiagnosticLevel.info}) → String -
Returns a string representation of this object.
inherited
-
toStringDeep(
{String prefixLineOne = '', String prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String -
Returns a string representation of this node and its descendants. [...]
inherited
-
toStringShallow(
{String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String -
Returns a one-line detailed description of the object. [...]
inherited
-
toStringShort(
) → String -
A short, textual description of this widget.
inherited
Operators
-
operator ==(
Object other) → bool -
The equality operator. [...]
@nonVirtual, inherited