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 a RenderAbstractViewports, such as Viewport or TwoDimensionalViewport.

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.

The same addAutomaticKeepAlives feature is supported by the TwoDimensionalChildBuilderDelegate and TwoDimensionalChildListDelegate.

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.



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


child Widget
The widget below this widget in the tree.
debugTypicalAncestorWidgetClass Type
Describes the RenderObjectWidget that is typically used to set up the ParentData that applyParentData will write to.
no setteroverride
debugTypicalAncestorWidgetDescription String
Describes the RenderObjectWidget that is typically used to set up the ParentData that applyParentData will write to.
no setteroverride
hashCode int
The hash code for this object.
no setterinherited
keepAlive bool
Whether to keep the child alive.
key Key?
Controls how one widget replaces another widget in the tree.
runtimeType Type
A representation of the runtime type of the object.
no setterinherited


applyParentData(RenderObject renderObject) → void
Write the data from this widget into the given render object's parent data.
createElement() ParentDataElement<KeepAliveParentDataMixin>
Inflates this configuration to a concrete instance.
debugCanApplyOutOfTurn() bool
Whether the ParentDataElement.applyWidgetOutOfTurn method is allowed with this widget.
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
debugIsValidRenderObject(RenderObject renderObject) bool
Checks if this widget can apply its parent data to the provided renderObject.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) DiagnosticsNode
Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep.
toString({DiagnosticLevel minLevel =}) String
A string representation of this object.
toStringDeep({String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) String
Returns a string representation of this node and its descendants.
toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) String
Returns a one-line detailed description of the object.
toStringShort() String
A short, textual description of this widget.


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