ReactterSelector<T extends Object?, V> class
A StatelessWidget similar to ReactterConsumer but allowing to control the rebuilding of widget tree by selecting the ReactterStates, and a computed value.
ReactterSelector determines if builder needs to be rebuild again by comparing the previous and new result of Selector and returns it. This evaluation only occurs if one of the selected ReactterStates gets updated, or by the instance if the selector does not have any selected ReactterStates.
The selector property has a two arguments, the first one is the instance
of T
type which is obtained from the closest ancestor ReactterProvider.
and the second one is a Select function which allows to wrapper any
ReactterStates to listen, and returns the value in each build. e.g:
ReactterSelector<MyController, double>(
selector: (MyController inst, Select $) {
final num1 = $(inst.intState).value;
final num2 = $(inst.doubleState).value;
return (num1 + num2).clamp(0, 100);
},
builder: (BuildContext context, MyController inst, double value, Widget? child) {
return Text('Computed value: $value');
},
)
It does not have the T
tyoe, it is necessary
to wrap the app with ReactterScope for it to work properly. e.g:
ReactterScope(
child: MyApp(),
)
// Now can use it without type like:
ReactterSelector(
selector: (_, $) => $(myListState).value.length,
builder: (context, _, itemCount, child) {
return ListView.builder(
itemCount: itemCount,
itemBuilder: (context, index) {
[...]
},
);
},
)
ReactterSelector has same functionality as ReactterSelector.contextOf.
Use id property to identify the T
instance.
Use child property to pass a Widget which to be built once only. It will be sent through the builder callback, so you can incorporate it into your build:
ReactterSelector<MyController, String>(
selector: (inst, $) => $(inst.strState).value.trim(),
child: Text("This widget build only once"),
builder: (context inst, value, child) {
return Column(
children: [
Text("value: $value"),
child,
],
);
},
)
See also:
- ReactterState, a state in reactter.
- ReactterConsumer, a widget that obtains an instance of
T
type from the closest ancestor ReactterProvider. - ReactterProvider, a widget that provides a
T
instance through Widget.
- Inheritance
-
- Object
- DiagnosticableTree
- Widget
- StatelessWidget
- ReactterSelector
Constructors
-
ReactterSelector({Key? key, String? id, required Selector<
T, V> selector, Widget? child, required InstanceValueBuilder<T, V> builder}) -
A StatelessWidget similar to ReactterConsumer but allowing to control
the rebuilding of widget tree by selecting the ReactterStates,
and a computed value.
const
Properties
-
builder
→ InstanceValueBuilder<
T, V> -
Method which is responsible for building the widget tree.
final
- child → Widget?
-
Use to pass a single child widget that will be built once
and incorporated into the widget tree.
final
- hashCode → int
-
The hash code for this object.
no setterinherited
- id → String?
-
This identifier can be used to differentiate
between multiple instances of the same
T
type in the widget tree when using ReactterProvider.final - 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
→ Selector<
T, V> -
Takes an instance of
T
type and a Select function, and returns a value ofR
type. It can be used to compute a value based on the provided arguments.final
Methods
-
build(
BuildContext context) → Widget -
Describes the part of the user interface represented by this widget.
override
-
createElement(
) → StatelessElement -
Creates a StatelessElement to manage this widget's location in the tree.
inherited
-
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}) → 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
Static Methods
-
contextOf<
T extends Object?, V> (BuildContext context, {String? id, required Selector< T, V> selector}) → V -
Uses the
selector
callback, for determining if the widget tree ofcontext
needs to be rebuild by comparaing the previous and new result ofselector
, and returns it. This evaluation only occurs if one of the selected ReactterStates gets updated, or by the instance if theselector
does not have any selected ReactterStates.