ExtendedTrackingScrollController class

A ExtendedScrollController whose initialScrollOffset tracks its most recently updated ScrollPosition.

This class can be used to synchronize the scroll offset of two or more lazily created scroll views that share a single ExtendedTrackingScrollController. It tracks the most recently updated scroll position and reports it as its initialScrollOffset.

{@tool snippet}

In this example each PageView page contains a ListView and all three ListView's share a ExtendedTrackingScrollController. The scroll offsets of all three list views will track each other, to the extent that's possible given the different list lengths.

PageView(
  children: <Widget>[
    ListView(
      controller: _trackingScrollController,
      children: List<Widget>.generate(100, (int i) => Text('page 0 item $i')).toList(),
    ),
    ListView(
      controller: _trackingScrollController,
      children: List<Widget>.generate(200, (int i) => Text('page 1 item $i')).toList(),
    ),
    ListView(
     controller: _trackingScrollController,
     children: List<Widget>.generate(300, (int i) => Text('page 2 item $i')).toList(),
    ),
  ],
)

{@end-tool}

In this example the _trackingController would have been created by the stateful widget that built the widget tree.

Inheritance

Constructors

ExtendedTrackingScrollController.new({double initialScrollOffset = 0.0, bool keepScrollOffset = true, String? debugLabel})
Creates a scroll controller that continually updates its initialScrollOffset to match the last scroll notification it received.

Properties

debugLabel → String?
A label that is used in the toString output. Intended to aid with identifying scroll controller instances in debug output.
finalinherited
hasClients → bool
Whether any ScrollPosition objects have attached themselves to the ExtendedScrollController using the attach method.
no setterinherited
hashCode → int
The hash code for this object.
no setterinherited
hasListeners → bool
Whether any listeners are currently registered.
no setterinherited
initialScrollOffset → double
Returns the scroll offset of the mostRecentlyUpdatedPosition or, if that is null, the initial scroll offset provided to the constructor.
no setteroverride
keepScrollOffset → bool
Each time a scroll completes, save the current scroll offset with PageStorage and restore it if this controller's scrollable is recreated.
finalinherited
mostRecentlyUpdatedPosition → ScrollPosition?
The last ScrollPosition to change. Returns null if there aren't any attached scroll positions, or there hasn't been any scrolling yet, or the last ScrollPosition to change has since been removed.
no setter
offset → double
The current scroll offset of the scrollable widget.
no setterinherited
position → ScrollPosition
Returns the attached ScrollPosition, from which the actual scroll offset of the ScrollView can be obtained.
no setterinherited
positions → Iterable<ScrollPosition>
The currently attached positions.
no setterinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

addListener(VoidCallback listener) → void
Register a closure to be called when the object changes.
inherited
animateTo(double offset, {required Duration duration, required Curve curve}) → Future<void>
Animates the position from its current value to the given value.
inherited
attach(ScrollPosition position) → void
Register the given position with this controller.
override
createScrollPosition(ScrollPhysics physics, ScrollContext context, ScrollPosition? oldPosition) → ScrollPosition
Creates a ScrollPosition for use by a Scrollable widget.
inherited
debugFillDescription(List<String> description) → void
Add additional information to the given description for use by toString.
inherited
detach(ScrollPosition position) → void
Unregister the given position with this controller.
override
dispose() → void
Discards any resources used by the object. After this is called, the object is not in a usable state and should be discarded (calls to addListener will throw after the object is disposed).
override
jumpTo(double value) → void
Jumps the scroll position from its current value to the given value, without animation, and without checking if the new value is in range.
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
notifyListeners() → void
Call all the registered listeners.
inherited
removeListener(VoidCallback listener) → void
Remove a previously registered closure from the list of closures that are notified when the object changes.
inherited
toString() → String
A string representation of this object.
inherited

Operators

operator ==(Object other) → bool
The equality operator.
inherited