RestorableValue<T> class Null safety

A RestorableProperty that makes the wrapped value accessible to the owning State object via the value getter and setter.

Whenever a new value is set, didUpdateValue is called. Subclasses should call notifyListeners from this method if the new value changes what toPrimitives returns.

Using a RestorableValue

A StatefulWidget that has a restorable int property.

To create a local project with this code sample, run:
flutter create --sample=widgets.RestorableValue.1 mysample

A StatefulWidget that has a restorable int property.

  // The current value of the answer is stored in a [RestorableProperty].
  // During state restoration it is automatically restored to its old value.
  // If no restoration data is available to restore the answer from, it is
  // initialized to the specified default value, in this case 42.
  final RestorableInt _answer = RestorableInt(42);

  @override
  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
    // All restorable properties must be registered with the mixin. After
    // registration, the answer either has its old value restored or is
    // initialized to its default value.
    registerForRestoration(_answer, 'answer');
  }

  void _incrementAnswer() {
    setState(() {
      // The current value of the property can be accessed and modified via
      // the value getter and setter.
      _answer.value += 1;
    });
  }

  @override
  void dispose() {
    // Properties must be disposed when no longer used.
    _answer.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return OutlinedButton(
      child: Text('${_answer.value}'),
      onPressed: _incrementAnswer,
    );
  }

Creating a subclass

This example shows how to create a new RestorableValue subclass, in this case for the Duration class.

class RestorableDuration extends RestorableValue<Duration> {
  @override
  Duration createDefaultValue() => const Duration();

  @override
  void didUpdateValue(Duration? oldValue) {
    if (oldValue == null || oldValue.inMicroseconds != value.inMicroseconds)
      notifyListeners();
  }

  @override
  Duration fromPrimitives(Object? data) {
    if (data != null) {
      return Duration(microseconds: data as int);
    }
    return const Duration();
  }

  @override
  Object toPrimitives() {
    return value.inMicroseconds;
  }
}

Constructors

RestorableValue()

Properties

enabled → bool: Whether the object currently returned by toPrimitives should be included in the restoration state. [...]
read-only, inherited
hashCode → int: The hash code for this object. [...]
read-only, inherited
hasListeners → bool: Whether any listeners are currently registered. [...]
@protected, read-only, inherited
isRegistered → bool: Whether this property is currently registered with a RestorationMixin.
@protected, read-only, inherited
runtimeType → Type: A representation of the runtime type of the object.
read-only, inherited
state → State<StatefulWidget>: The State object that this property is registered with. [...]
@protected, read-only, inherited
value ↔ T: The current value stored in this property. [...]
read / write

Methods

addListener(VoidCallback listener) → void: Register a closure to be called when the object changes. [...]
inherited
createDefaultValue() → T: Called by the RestorationMixin if no restoration data is available to restore the value of the property from to obtain the default value for the property. [...]
inherited
didUpdateValue(T? oldValue) → void: Called whenever a new value is assigned to value. [...]
@protected
dispose() → void: Discards any resources used by the object. After this is called, the object is not in a usable state and should be discarded (calls to addListener and removeListener will throw after the object is disposed). [...]
inherited
fromPrimitives(Object? data) → T: Called by the RestorationMixin to convert the data previously retrieved from toPrimitives back into an object of type T that this property should wrap. [...]
inherited
initWithValue(T value) → void: Called by the RestorationMixin with the value returned by either createDefaultValue or fromPrimitives to set the value that this property currently wraps. [...]
@mustCallSuper, override
noSuchMethod(Invocation invocation) → dynamic: Invoked when a non-existent method or property is accessed. [...]
inherited
notifyListeners() → void: Call all the registered listeners. [...]
@protected, @visibleForTesting, inherited
removeListener(VoidCallback listener) → void: Remove a previously registered closure from the list of closures that are notified when the object changes. [...]
inherited
toPrimitives() → Object?: Called by the RestorationMixin to retrieve the information that this property wants to store in the restoration data. [...]
inherited
toString() → String: A string representation of this object. [...]
inherited

Operators

operator ==(Object other) → bool: The equality operator. [...]
inherited

widgets library