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<item value="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 [ScrollUpdateNotification]s, which indicate that the widget has changed its scroll position, mixed with zero or more [OverscrollNotification]s, 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 [ScrollUpdateNotification]s and [OverscrollNotification]s are zero or more [UserScrollNotification]s, 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. To drive layout based on the scroll position, consider listening to the [ScrollPosition] directly (or indirectly via a [ScrollController])." />
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