ScrollNotificationObserver class Null safety

Notifies its listeners when a descendant scrolls.

To add a listener to a ScrollNotificationObserver ancestor:

ScrollNotificationObserver.of(context).addListener(_listener);

To remove the listener from a ScrollNotificationObserver ancestor:

ScrollNotificationObserver.of(context).removeListener(_listener);

Stateful widgets that share an ancestor ScrollNotificationObserver typically add a listener in State.didChangeDependencies (removing the old one if necessary) and remove the listener in their State.dispose method.

Any function with the ScrollNotificationCallback signature can act as a listener:

// (e.g. in a stateful widget)
void _listener(ScrollNotification notification) {
  // Do something, maybe setState()
}

This widget is similar to NotificationListener. It supports a listener list instead of just a single listener and its listeners run unconditionally, they do not require a gating boolean return value.

Inheritance

Constructors

ScrollNotificationObserver({Key? key, required Widget child})
Create a ScrollNotificationObserver.
const

Properties

child Widget
The subtree below this widget.
final
hashCode int
The hash code for this object.
read-onlyinherited
key Key?
Controls how one widget replaces another widget in the tree.
finalinherited
runtimeType Type
A representation of the runtime type of the object.
read-onlyinherited

Methods

createElement() StatefulElement
Creates a StatefulElement to manage this widget's location in the tree.
inherited
createState() ScrollNotificationObserverState
Creates the mutable state for this widget at a given 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 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
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.
inherited

Static Methods

maybeOf(BuildContext context) ScrollNotificationObserverState?
The closest instance of this class that encloses the given context.
of(BuildContext context) ScrollNotificationObserverState
The closest instance of this class that encloses the given context.