JoltSelector<T> class

A widget that rebuilds only when a specific selector function's result changes.

JoltSelector provides fine-grained control over when rebuilds occur by watching a selector function. The widget only rebuilds when the selector's return value changes, making it more efficient than JoltBuilder for scenarios where you only need to react to specific derived values.

The selector function receives the previous selected value (or null on first run) and returns the new value to watch. Rebuilds occur only when the returned value changes (using equality comparison).

When to Use

Use JoltSelector when you need to:

  • Select a specific value from a complex object
  • Filter or transform reactive data before rebuilding
  • Avoid unnecessary rebuilds when unrelated parts of a signal change

For general reactive UI needs, JoltBuilder is simpler and recommended.

Parameters

  • builder: Function that builds the widget tree. Receives the context and the current selected value.
  • selector: Function that computes the value to watch for changes. Receives the previous selected value (or null on first run) and returns the new value.

Example

final user = Signal(User(name: 'John', age: 30));

// Only rebuilds when the user's name changes, not age
JoltSelector(
  selector: (prev) => user.value.name,
  builder: (context, name) => Text('Hello $name'),
)

With multiple signals:

final firstName = Signal('John');
final lastName = Signal('Doe');

JoltSelector(
  selector: (prev) => '${firstName.value} ${lastName.value}',
  builder: (context, fullName) => Text('Hello $fullName'),
)
Inheritance

Constructors

JoltSelector({Key? key, required Widget builder(BuildContext context, T state), required T selector(T? prevState)})
const

Properties

builder → Widget Function(BuildContext context, T state)
Function that builds the widget tree.
final
hashCode → int
The hash code for this object.
no setterinherited
key → Key?
Controls how one widget replaces another widget in the tree.
finalinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
selector → T Function(T? prevState)
Function that computes the value to watch for changes.
final

Methods

createElement() → JoltSelectorElement<T>
Inflates this configuration to a concrete instance.
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