RawScrollbar class Null safety

An extendable base class for building scrollbars that fade in and out.

To add a scrollbar to a ScrollView, like a ListView or a CustomScrollView, wrap the scroll view widget in a RawScrollbar widget.

A scrollbar thumb indicates which portion of a ScrollView is actually visible.

By default, the thumb will fade in and out as the child scroll view scrolls. When isAlwaysShown is true, the scrollbar thumb will remain visible without the fade animation. This requires that the ScrollController associated with the Scrollable widget is provided to controller, or that the PrimaryScrollController is being used by that Scrollable widget.

If the scrollbar is wrapped around multiple ScrollViews, it only responds to the nearest ScrollView and shows the corresponding scrollbar thumb by default. The notificationPredicate allows the ability to customize which ScrollNotifications the Scrollbar should listen to.

If the child ScrollView is infinitely long, the RawScrollbar will not be painted. In this case, the scrollbar cannot accurately represent the relative location of the visible area, or calculate the accurate delta to apply when dragging on the thumb or tapping on the track.

Interaction

Scrollbars are interactive and can use the PrimaryScrollController if a controller is not set. Interactive Scrollbar thumbs can be dragged along the main axis of the ScrollView to change the ScrollPosition. Tapping along the track exclusive of the thumb will trigger a ScrollIncrementType.page based on the relative position to the thumb.

When using the PrimaryScrollController, it must not be attached to more than one ScrollPosition. ScrollViews that have not been provided a ScrollController and have a ScrollView.scrollDirection of Axis.vertical will automatically attach their ScrollPosition to the PrimaryScrollController. Provide a unique ScrollController to each Scrollable in this case to prevent having multiple ScrollPositions attached to the PrimaryScrollController.

This sample shows an app with two scrollables in the same route. Since by default, there is one PrimaryScrollController per route, and they both have a scroll direction of Axis.vertical, they would both try to attach to that controller. The Scrollbar cannot support multiple positions attached to the same controller, so one ListView, and its Scrollbar have been provided a unique ScrollController.

Alternatively, a new PrimaryScrollController could be created above one of the ListViews.

To create a local project with this code sample, run:
flutter create --sample=material.RawScrollbar.1 mysample

Automatic Scrollbars on Desktop Platforms

Scrollbars are added to most Scrollable widgets by default on TargetPlatformVariant.desktop platforms. This is done through ScrollBehavior.buildScrollbar as part of an app's ScrollConfiguration. Scrollables that do not use the PrimaryScrollController or have a ScrollController provided to them will receive a unique ScrollController for use with the Scrollbar. In this case, only one Scrollable can be using the PrimaryScrollController, unless interactive is false. To prevent Axis.vertical Scrollables from using the PrimaryScrollController, set ScrollView.primary to false. Scrollable widgets that do not have automatically applied Scrollbars include

This sample shows a RawScrollbar that executes a fade animation as scrolling occurs. The RawScrollbar will fade into view as the user scrolls, and fade out when scrolling stops. The GridView uses the PrimaryScrollController since it has an Axis.vertical scroll direction and has not been provided a ScrollController.
To create a local project with this code sample, run:
flutter create --sample=widgets.RawScrollbar.2 mysample

When isAlwaysShown is true, the scrollbar thumb will remain visible without the fade animation. This requires that a ScrollController is provided to controller for both the RawScrollbar and the GridView. Alternatively, the PrimaryScrollController can be used automatically so long as it is attached to the singular ScrollPosition associated with the GridView.
To create a local project with this code sample, run:
flutter create --sample=widgets.RawScrollbar.3 mysample

See also:

  • ListView, which displays a linear, scrollable list of children.
  • GridView, which displays a 2 dimensional, scrollable array of children.
Inheritance
Implementers

Constructors

RawScrollbar({Key? key, required Widget child, ScrollController? controller, bool? isAlwaysShown, Radius? radius, double? thickness, Color? thumbColor, double minThumbLength, double? minOverscrollLength, Duration fadeDuration, Duration timeToFade, Duration pressDuration, ScrollNotificationPredicate notificationPredicate, bool? interactive, ScrollbarOrientation? scrollbarOrientation, double mainAxisMargin, double crossAxisMargin})
Creates a basic raw scrollbar that wraps the given child. [...]
const

Properties

child Widget
The widget below this widget in the tree. [...]
final
controller ScrollController?
The ScrollController used to implement Scrollbar dragging. [...]
final
crossAxisMargin double
Distance from the scrollbar thumb side to the nearest cross axis edge in logical pixels. [...]
final
fadeDuration Duration
The Duration of the fade animation. [...]
final
hashCode int
The hash code for this object. [...]
@nonVirtual, read-only, inherited
interactive bool?
Whether the Scrollbar should be interactive and respond to dragging on the thumb, or tapping in the track area. [...]
final
isAlwaysShown bool?
Indicates that the scrollbar should be visible, even when a scroll is not underway. [...]
final
key Key?
Controls how one widget replaces another widget in the tree. [...]
final, inherited
mainAxisMargin double
Distance from the scrollbar's start and end to the edge of the viewport in logical pixels. It affects the amount of available paint area. [...]
final
minOverscrollLength double?
The preferred smallest size the scrollbar thumb can shrink to when viewport is overscrolled. [...]
final
minThumbLength double
The preferred smallest size the scrollbar thumb can shrink to when the total scrollable extent is large, the current visible viewport is small, and the viewport is not overscrolled. [...]
final
notificationPredicate ScrollNotificationPredicate
A check that specifies whether a ScrollNotification should be handled by this widget. [...]
final
pressDuration Duration
The Duration of time that a LongPress will trigger the drag gesture of the scrollbar thumb. [...]
final
radius Radius?
The Radius of the scrollbar thumb's rounded rectangle corners. [...]
final
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited
scrollbarOrientation ScrollbarOrientation?
Dictates the orientation of the scrollbar. [...]
final
thickness double?
The thickness of the scrollbar in the cross axis of the scrollable. [...]
final
thumbColor Color?
The color of the scrollbar thumb. [...]
final
timeToFade Duration
The Duration of time until the fade animation begins. [...]
final

Methods

createElement() StatefulElement
Creates a StatefulElement to manage this widget's location in the tree. [...]
inherited
createState() RawScrollbarState<RawScrollbar>
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. [...]
@protected, 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. [...]
@nonVirtual, inherited