A Notification related to scrolling.
Scrollable widgets notify their ancestors about scrolling-related changes. The notifications have the following lifecycle:
- A ScrollStartNotification, which indicates that the widget has started scrolling.
- Zero or more ScrollUpdateNotifications, which indicate that the widget has changed its scroll position, mixed with zero or more OverscrollNotifications, which indicate that the widget has not changed its scroll position because the change would have caused its scroll position to go outside its scroll bounds.
- Interspersed with the ScrollUpdateNotifications and OverscrollNotifications are zero or more UserScrollNotifications, which indicate that the user has changed the direction in which they are scrolling.
- A ScrollEndNotification, which indicates that the widget has stopped scrolling.
- A UserScrollNotification, with a UserScrollNotification.direction of ScrollDirection.idle.
Notifications bubble up through the tree, which means a given NotificationListener will receive notifications for all descendant Scrollable widgets. To focus on notifications from the nearest Scrollable descendant, check that the depth property of the notification is zero.
When a scroll notification is received by a NotificationListener, the listener will have already completed build and layout, and it is therefore too late for that widget to call State.setState. Any attempt to adjust the build or layout based on a scroll notification would result in a layout that lagged one frame behind, which is a poor user experience. Scroll notifications are therefore primarily useful for paint effects (since paint happens after layout). The GlowingOverscrollIndicator and Scrollbar widgets are examples of paint effects that use scroll notifications.
- context → BuildContext
The build context of the widget that fired this notification. [...]
- metrics → ScrollMetrics
A description of a
Scrollable's contents, useful for modeling the state of its viewport.final
- depth → int
The number of viewports that this notification has bubbled through. [...]
- hashCode → int
The hash code for this object. [...]
- runtimeType → Type
A representation of the runtime type of the object.
List< String>description) → void
BuildContext target) → void
Start bubbling this notification at the given build context. [...]
Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed. [...]
) → String
Returns a string representation of this object.
Element element) → bool
Applied to each ancestor of the dispatch target. [...]