Observer<T> class

A widget that rebuilds when a reactive variable changes.

Observer automatically listens to a Reactive variable and rebuilds its child widget whenever the variable's value changes. This provides a declarative way to create reactive UI without manually managing listeners.

The widget is lightweight and efficient, using Flutter's ValueListenableBuilder internally for optimal performance.

Example:

final counter = Reactive<int>(0);

Observer<int>(
  listenable: counter,
  listener: (value) => Text('Count: $value'),
);

// Updates automatically when counter changes
counter.value++;

For nullable types, use ObserverN instead.

Inheritance
Annotations
  • @Deprecated('Use ReactiveBuilder instead. Observer will be removed in a future version.')

Constructors

Observer({Key? key, required Reactive<T> listenable, required Widget listener(T value)})
Creates an Observer widget.
const

Properties

hashCode → int
The hash code for this object.
no setterinherited
key → Key?
Controls how one widget replaces another widget in the tree.
finalinherited
listenable → Reactive<T>
The reactive variable to observe for changes.
final
listener → Widget Function(T value)
Builder function called with the current value whenever it changes.
final
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

createElement() → StatefulElement
Creates a StatefulElement to manage this widget's location in the tree.
inherited
createState() → State<Observer<T>>
Creates the mutable state for this widget at a given location in the tree.
override
debugDescribeChildren() → List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent 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, int wrapWidth = 65}) → 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.
inherited