SubValue<T> class

Creates, recreates, updates and disposes a Value T.

SubValue calls create to create a value. The created value is provided to its child widgets through the builder.

Changing the return value of keys will trigger another call to create. The updated value is then passed to builder and the widget is rebuilt. If no value is passed for keys, the value is created once only and persist for the lifetime of this widget.

The value can be updated by specifying the update parameter. This is useful if the created value is a controller, and its values rely on other variables up in the tree.

To release any allocated resources, the value can be disposed with the dispose callback. dispose is called for every value that is discarded when keys change and once this widget is disposed entirely.

The following example SubValue shows an example of creating a Stream for a search from our database. The stream is recreated when either the database or the search changes. The Stream can then be used in a StreamBuilder. The stream is appropriately kept in a State while we do not need an extra StatefulWidget.

return SubValue(
  create: () => database.findItems(search),
  keys: [database, search],
  builder: (context, stream) => StreamBuilder(
    stream: stream,
    builder: (context, snapshot) => /* ... */,
  ),
);

Inheritance

• Object
• DiagnosticableTree
• Widget
• StatefulWidget
• SubValue

Implementers

• SubAnimationController
• SubDefault
• SubDisposableListenable
• SubEffect
• SubFuture
• SubListener
• SubMemoized
• SubStream
• SubStreamController
• SubSubscriber
• SubTickerProvider

Constructors

SubValue({required SubValueCreate<T> create, SubValueKeys? keys, SubValueUpdate<T>? update, SubValueDispose<T>? dispose, required SubValueBuild<T> builder})

Creates, recreates, updates and disposes a Value T.

SubValue.builder({required SubValueBuilderCreate<T> create, SubValueBuilderKeys? keys, SubValueBuilderUpdate<T>? update, SubValueBuilderDispose<T>? dispose, required SubValueBuild<T> builder})

Creates, recreates, updates and disposes a Value T.

const

Properties

builder → SubValueBuild<T>

Creates the child of this Widget with the value.

final

create → SubValueBuilderCreate<T>

Creates the value. Called at least once and everytime keys changes.

final

dispose → SubValueBuilderDispose<T>?

Disposes the value. Called before recreation and when disposing. Useful for Listeners, etc.

final

hashCode → int

The hash code for this object.

no setter, inherited

key → Key?

Controls how one widget replaces another widget in the tree.

final, inherited

keys → SubValueBuilderKeys?

Used to decide when to recreate the value. If null, the value is never recreated.

final

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

update → SubValueBuilderUpdate<T>?

Updates the value. Called every build. If null, does nothing. In the call order, this comes after recreating the value.

final

Methods

createElement() → StatefulElement

Creates a StatefulElement to manage this widget's location in the tree.

inherited

createState() → State<SubValue<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}) → 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