Scrollable class

A widget that manages scrolling in one dimension and informs the Viewport through which the content is viewed.

Scrollable implements the interaction model for a scrollable widget, including gesture recognition, but does not have an opinion about how the viewport, which actually displays the children, is constructed.

It's rare to construct a Scrollable directly. Instead, consider ListView or GridView, which combine scrolling, viewporting, and a layout model. To combine layout models (or to use a custom layout mode), consider using CustomScrollView.

The static Scrollable.of and Scrollable.ensureVisible functions are often used to interact with the Scrollable widget inside a ListView or a GridView.

To further customize scrolling behavior with a Scrollable:

1. You can provide a viewportBuilder to customize the child model. For example, SingleChildScrollView uses a viewport that displays a single box child whereas CustomScrollView uses a Viewport or a ShrinkWrappingViewport, both of which display a list of slivers.

2. You can provide a custom ScrollController that creates a custom ScrollPosition subclass. For example, PageView uses a PageController, which creates a page-oriented scroll position subclass that keeps the same page visible when the Scrollable resizes.

Persisting the scroll position during a session

Scrollables attempt to persist their scroll position using PageStorage. This can be disabled by setting ScrollController.keepScrollOffset to false on the controller. If it is enabled, using a PageStorageKey for the key of this widget (or one of its ancestors, e.g. a ScrollView) is recommended to help disambiguate different Scrollables from each other.

See also:

• ListView, which is a commonly used ScrollView that displays a scrolling, linear list of child widgets.
• PageView, which is a scrolling list of child widgets that are each the size of the viewport.
• GridView, which is a ScrollView that displays a scrolling, 2D array of child widgets.
• CustomScrollView, which is a ScrollView that creates custom scroll effects using slivers.
• SingleChildScrollView, which is a scrollable widget that has a single child.
• ScrollNotification and NotificationListener, which can be used to watch the scroll position without using a ScrollController.