Watcher<T> class

A ChangeNotifier that holds a single value.

When value is replaced with something that is not equal to the old value as evaluated by the equality operator ==, this class notifies its listeners.

When safeMode is enabled, and this isDisposed, any notifyListeners, or setting new value will be ignored.

Limitations

Because this class only notifies listeners when the value's identity changes, listeners will not be notified when mutable state within the value itself changes.

While there is custom watcher types that helps reusing this limitation like ListWatcher, MapWatcher, SetWatcher, etc, When working with custom objects/types like changing variable inside your instance, you need to manually using refresh, or notifyListeners.

As a result, this class is best used with only immutable data types.

For mutable data types, consider using the watcher_classes or extending ChangeNotifier directly.

Inheritance

Implemented types

ValueListenable<T>

Implementers

Available extensions

Constructors

Watcher(T _value, {bool safeMode = true}): Creates a ChangeNotifier that wraps this value.

Properties

hashCode → int: The hash code for this object.
no setterinherited
hasListeners → bool: Whether any listeners are currently registered.
no setterinherited
isDisposed → bool: Flag which returns true if you called the dispose method. It is useful when you want to safely do some operations on the Watcher without getting an exception if it gets disposed.
no setter
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited
safeMode → bool: safeMode if enabled will not allow any setting of value or notifying any listeners if the Watcher isDisposed
final
stream → Stream<T>: Converts the Watcher into a Stream. This stream emits values whenever the value changes. The use of distinct ensures that consecutive duplicate values are filtered out, thus the stream only emits when the value actually changes.
no setter
v ↔ T: Equivalent to the getter value but in shorter syntax.
getter/setter pair
value ↔ T: The current value stored in this watcher.
getter/setter pairoverride-getter

Methods

addListener(VoidCallback listener) → void: Register a closure to be called when the object changes.
inherited
debounce(Duration duration, void action(T value)) → VoidCallback: Registers a debounced callback which is invoked only after the notifier's value is stable for the specified duration.
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 will throw after the object is disposed).
override
noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
notifyListeners() → void: Call all the registered listeners.
override
onChange(void action(T value)) → VoidCallback: Registers a callback to be invoked whenever the ValueNotifier's value changes.
refresh() → void: Rebuilds and trigger any listeners of any WatchValue or watch attached to that Watcher.
removeListener(VoidCallback listener) → void: Remove a previously registered closure from the list of closures that are notified when the object changes.
inherited
setWithoutNotify(T newValue) → void
toString() → String: A string representation of this object.
override
updateIf(bool condition(T), T newValue) → void: Updates the ValueNotifier's value to newValue if condition returns true.
updateOnAction<R>(R action()) → R: Will notifyListeners after a specific action has been made, and optionally return a result R of certain type.

Operators

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