Computed<T> class

A reactive class that computes a value on demand and notifies listeners when the value changes.

This class acts as both a ReactiveNotifier and a Watcher, allowing it to observe dependencies and recompute its value when those dependencies change. The computation is only triggered when value is accessed.

Features:

Lazy Computation: The value is computed only when accessed.
Automatic Dependency Tracking: Recomputes when observed values change.
Efficient Updates: Notifies listeners only if the computed value changes.

Example Usage:

// Create reactive state variables
final count = Ref<int>(0);
final doubleCount = Computed(() => count.value * 2);

// Access computed value (triggers computation)
print(doubleCount.value); // Output: 0

// Update dependency
count.value = 5;

// Computed value updates automatically
print(doubleCount.value); // Output: 10

// Reactivity: Automatically recomputes when `count` changes
watchEffect(() {
  print('Double count changed: ${doubleCount.value}');
});

Notes:

The computation is cached until dependencies change.
Call force(value) to manually override the computed value.

Inheritance

Mixed-in types

WatcherRaw<T>
Watcher<T>

Constructors

Computed.new(T _getValue()): Creates a new Computed object that computes its value using getValue.

Properties

computes ↔ Map<int, Picker>: A map of computes that are used by this watcher.
getter/setter pairinherited
currentIndexCompute ↔ int: The current index of the compute being used.
getter/setter pairinherited
dryRun ↔ T Function(): A function that is called to track dependencies.
latefinalinherited
hashCode → int: The hash code for this object.
no setterinherited
hasListeners → bool: Whether any listeners are currently registered.
no setterinherited
mounted → bool: Whether the notifier is mounted.
no setterinherited
onChange ↔ VoidCallback: A callback that is called when the watcher's dependencies change.
latefinalinherited
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited
value → T: Returns the computed value, computing it if necessary.
no setteroverride
watchers ↔ Set<ReactiveNotifier>: The set of notifiers that this watcher is listening to.
getter/setter pairinherited

Methods

addDepend(ReactiveNotifier ref) → void: Adds a dependency to this watcher.
inherited
addListener(VoidCallback listener) → void: Adds a listener and ensures computation is performed before notifying.
override
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).
inherited
dispose2() → void: Disposes of the watcher.
inherited
force(T value) → void: Manually overrides the computed value and forces an update.
getCC() → Picker?: Gets the current compute.
inherited
noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
notify() → void: Notifies listeners of a change.
notifyListeners() → void: Call all the registered listeners.
inherited
onCleanup(VoidCallback callback) → void: Registers a cleanup function to be called when the watcher is disposed.
inherited
removeListener(VoidCallback listener) → void: Remove a previously registered closure from the list of closures that are notified when the object changes.
inherited
run() → T: Runs the watcher and returns the result.
inherited
select<U>(U getter(T value)) → Computed<U>: Creates a Computed that selects a value from the notifier.
inherited
setCC(Picker cc) → Picker: Sets the current compute.
inherited
toString() → String: Returns a string representation of the computed value.
override

Operators

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