Scrollbar class

A Material Design scrollbar.

To add a scrollbar to a ScrollView, wrap the scroll view widget in a Scrollbar 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 thumbVisibility 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.

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

• EditableText
• ListWheelScrollView
• PageView
• NestedScrollView
• DropdownButton

Default Scrollbars can be disabled for the whole app by setting a ScrollBehavior with scrollbars set to false.

MaterialApp(
  scrollBehavior: const MaterialScrollBehavior()
    .copyWith(scrollbars: false),
  home: Scaffold(
    appBar: AppBar(title: const Text('Home')),
  ),
)

Dynamically changes to a CupertinoScrollbar, an iOS style scrollbar, by default on the iOS platform.

The color of the Scrollbar thumb will change when WidgetState.dragged, or WidgetState.hovered on desktop and web platforms. These stateful color choices can be changed using ScrollbarThemeData.thumbColor.

A scrollbar track can be added using trackVisibility. This can also be drawn when triggered by a hover event, or based on any WidgetState by using ScrollbarThemeData.trackVisibility.

The thickness of the track and scrollbar thumb can be changed dynamically in response to WidgetStates using ScrollbarThemeData.thickness.

See also:

• RawScrollbar, a basic scrollbar that fades in and out, extended by this class to add more animations and behaviors.
• ScrollbarTheme, which configures the Scrollbar's appearance.
• CupertinoScrollbar, an iOS style scrollbar.
• ListView, which displays a linear, scrollable list of children.
• GridView, which displays a 2 dimensional, scrollable array of children.