CellHooks mixin

Provides the cell method for creating and retrieving instances of ValueCell's.

The cell method can be used within build to obtain an instance of a ValueCell that is persisted between builds of the widget.

During the first build every call to cell will create a new ValueCell instance using the provided cell creation function. In subsequent builds calls to cell return the existing instance that was created during the first build using the corresponding cell creation function.

Example:

class Example extends CellWidget {
  @override
  Widget build(BuildContext context) {
    final a = cell(() => MutableCell(0));
    final b = cell(() => MutableCell(1));

    final sum = cell(() => a + b);
    final product = cell(() => a * b);

    return Column(
      children: [
         Text('a + b = ${sum()}'),
         Text('a * b = ${product()}')
         ...
      ]
    );
  }
}

In the example above, when the widget is built for the first time, two mutable cells are created and assigned to a and b, and two computed cells a + b, a * b are assigned to sum and product, respectively. In subsequent builds, the first two calls to cell return the same MutableCell instances created during the first build and cell(() => a + b) returns the existing instance of the cell a + b, while cell(() => a * b) returns the existing instance of the cell a * b.

With this class cell definitions can be kept directly within the build function without having to use a StatefulWidget.

NOTE:

Uses of cell have to obey the following rules:

  1. Calls to cell must not appear within conditionals or loops.
  2. Calls to cell must not appear within widget builder functions, such as those used with Builder or ValueListenableBuilder.
Superclass constraints

Properties

hashCode → int
The hash code for this object.
no setterinherited
key → Key?
Controls how one widget replaces another widget in the tree.
finalinherited
restorationId → String?
Restoration ID to use for restoring the cell state
finalinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

build(BuildContext context) → Widget
Describes the part of the user interface represented by this widget.
inherited
cell<T, V extends ValueCell<T>>(CreateCell<V> create) → V
Return an instance of a ValueCell that is kept between builds of the widget.
createElement() → StatelessElement
Creates a StatelessElement to manage this widget's 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
watch(VoidCallback watch) → void
Register a callback to be called whenever the values of cells change.

Operators

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