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.



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


keepAlive bool
Whether to keep the child alive. [...]
child Widget
The widget below this widget in the tree. [...]
final, inherited
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


applyParentData(RenderObject renderObject) → void
Write the data from this widget into the given render object's parent data. [...]
debugCanApplyOutOfTurn() bool
Whether the ParentDataElement.applyWidgetOutOfTurn method is allowed with this widget. [...]
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node. [...]
createElement() ParentDataElement<SliverWithKeepAliveWidget>
Inflates this configuration to a concrete instance. [...]
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children. [...]
@protected, inherited
debugDescribeInvalidAncestorChain({String description, String ownershipChain, bool foundValidAncestor, Iterable<Widget> badAncestors }) String
Subclasses should override this to describe the requirements for using the ParentDataWidget subclass. It is called when debugIsValidAncestor() returned false for an ancestor, or when there are extraneous ParentDataWidgets in the ancestor chain.
debugIsValidAncestor(RenderObjectWidget ancestor) bool
Subclasses should override this method to return true if the given ancestor is a RenderObjectWidget that wraps a RenderObject that can handle the kind of ParentData widget that the ParentDataWidget subclass handles. [...]
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent 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 toStringDeep. [...]
toString({DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns 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 ==(dynamic other) bool
The equality operator. [...]