ChangeNotifierProvider<T extends ChangeNotifier?> class Null safety

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 inside create.

ChangeNotifierProvider(
  create: (_) => new MyChangeNotifier(),
  child: ...
)

• DON'T use ChangeNotifierProvider.value to create your ChangeNotifier.

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
• DiagnosticableTree
• Widget
• StatelessWidget
• SingleChildStatelessWidget
• InheritedProvider<T>
• ListenableProvider<T>
• ChangeNotifierProvider

Constructors

ChangeNotifierProvider({Key? key, required Create<T> create, bool? lazy, TransitionBuilder? builder, Widget? child})

Creates a ChangeNotifier using create and automatically disposes 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

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