ValueListenableBuilder< T> class
A widget whose content stays sync'ed with a ValueListenable.
Given a ValueListenable<T> and a builder which builds widgets from
concrete values of T
, this class will automatically register itself as a
listener of the ValueListenable and call the builder with updated values
when the value changes.
Performance optimizations
If your builder function contains a subtree that does not depend on the value of the ValueListenable, it's more efficient to build that subtree once instead of rebuilding it on every animation tick.
If you pass the pre-built subtree as the child parameter, the ValueListenableBuilder will pass it back to your builder function so that you can incorporate it into your build.
Using this pre-built child is entirely optional, but can improve performance significantly in some cases and is therefore a good practice.
See also:
- AnimatedBuilder, which also triggers rebuilds from a Listenable without passing back a specific value from a ValueListenable.
- NotificationListener, which lets you rebuild based on Notification coming from its descendent widgets rather than a ValueListenable that you have a direct reference to.
- StreamBuilder, where a builder can depend on a Stream rather than a ValueListenable for more advanced use cases.
- Inheritance
- Object
- Diagnosticable
- DiagnosticableTree
- Widget
- StatefulWidget
- ValueListenableBuilder
Constructors
-
ValueListenableBuilder({@required ValueListenable<
T> valueListenable, @required ValueWidgetBuilder< T> builder, Widget child }) -
Creates a ValueListenableBuilder. [...]
const
Properties
-
builder
→ ValueWidgetBuilder<
T> -
A ValueWidgetBuilder which builds a widget depending on the
valueListenable's value. [...]
final
- child → Widget
-
A valueListenable-independent widget which is passed back to the builder. [...]
final
-
valueListenable
→ ValueListenable<
T> -
The ValueListenable whose value you depend on in order to build. [...]
final
- hashCode → int
-
The hash code for this object. [...]
read-only, inherited
- key → Key
-
Controls how one widget replaces another widget in the tree. [...]
final, inherited
- runtimeType → Type
-
A representation of the runtime type of the object.
read-only, inherited
Methods
-
createState(
) → State< StatefulWidget> -
Creates the mutable state for this widget at a given location in the tree. [...]
override
-
createElement(
) → StatefulElement -
Creates a StatefulElement to manage this widget's location in the tree. [...]
inherited
-
debugDescribeChildren(
) → List< DiagnosticsNode> -
Returns a list of DiagnosticsNode objects describing this node's
children. [...]
@protected, inherited
-
debugFillProperties(
DiagnosticPropertiesBuilder properties) → void -
Add additional properties associated with the node. [...]
inherited
-
noSuchMethod(
Invocation invocation) → dynamic -
Invoked when a non-existent 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 toStringDeep. [...]
inherited
-
toString(
{DiagnosticLevel minLevel: DiagnosticLevel.debug }) → String -
Returns 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 ==(
dynamic other) → bool -
The equality operator. [...]
inherited