KeepAlive class

Mark a child as needing to stay alive even when it's in a lazy list that would otherwise remove it.

This widget is for use in SliverWithKeepAliveWidgets, such as SliverGrid or SliverList.

This widget is rarely used directly. The SliverChildBuilderDelegate and SliverChildListDelegate delegates, used with SliverList and SliverGrid, as well as the scroll view counterparts ListView and GridView, have an addAutomaticKeepAlives feature, which is enabled by default, and which causes AutomaticKeepAlive widgets to be inserted around each child, causing KeepAlive widgets to be automatically added and configured in response to KeepAliveNotifications.

Therefore, to keep a widget alive, it is more common to use those notifications than to directly deal with KeepAlive widgets.

In practice, the simplest way to deal with these notifications is to mix AutomaticKeepAliveClientMixin into one's State. See the documentation for that mixin class for details.

Inheritance

Constructors

KeepAlive({Key key, @required bool keepAlive, @required Widget child})
Marks a child as needing to remain alive. [...]
const

Properties

debugTypicalAncestorWidgetClass Type
The RenderObjectWidget that is typically used to set up the ParentData that applyParentData will write to. [...]
read-only, override
keepAlive bool
Whether to keep the child alive. [...]
final
child Widget
The widget below this widget in the tree. [...]
final, inherited
hashCode int
The hash code for this object. [...]
@nonVirtual, 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

applyParentData(RenderObject renderObject) → void
Write the data from this widget into the given render object's parent data. [...]
override
debugCanApplyOutOfTurn() bool
Whether the ParentDataElement.applyWidgetOutOfTurn method is allowed with this widget. [...]
override
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node. [...]
override
createElement() ParentDataElement<KeepAliveParentDataMixin>
Inflates this configuration to a concrete instance. [...]
inherited
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
@protected, inherited
debugIsValidRenderObject(RenderObject renderObject) bool
Checks if this widget can apply its parent data to the provided renderObject. [...]
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 DiagnosticsNode.toStringDeep.
inherited
toString({DiagnosticLevel minLevel: DiagnosticLevel.info}) 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 ==(Object other) bool
The equality operator. [...]
@nonVirtual, inherited