// Copyright 2014 The Flutter Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. import 'dart:async'; import 'dart:math' as math; import 'package:flutter/foundation.dart'; import 'package:flutter/gestures.dart'; import 'package:flutter/rendering.dart'; import 'package:flutter/scheduler.dart'; import 'package:flutter/services.dart'; import 'basic.dart'; import 'framework.dart'; import 'gesture_detector.dart'; import 'media_query.dart'; import 'notification_listener.dart'; import 'restoration.dart'; import 'restoration_properties.dart'; import 'scroll_activity.dart'; import 'scroll_configuration.dart'; import 'scroll_context.dart'; import 'scroll_controller.dart'; import 'scroll_physics.dart'; import 'scroll_position.dart'; import 'scrollable_helpers.dart'; import 'selectable_region.dart'; import 'selection_container.dart'; import 'ticker_provider.dart'; import 'viewport.dart'; export 'package:flutter/physics.dart' show Tolerance; // Examples can assume: // late BuildContext context; /// Signature used by [Scrollable] to build the viewport through which the /// scrollable content is displayed. typedef ViewportBuilder = Widget Function(BuildContext context, ViewportOffset position); /// A widget that scrolls. /// /// [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. /// /// 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]. class Scrollable extends StatefulWidget { /// Creates a widget that scrolls. /// /// The [axisDirection] and [viewportBuilder] arguments must not be null. const Scrollable({ super.key, this.axisDirection = AxisDirection.down, this.controller, this.physics, required this.viewportBuilder, this.incrementCalculator, this.excludeFromSemantics = false, this.semanticChildCount, this.dragStartBehavior = DragStartBehavior.start, this.restorationId, this.scrollBehavior, this.clipBehavior = Clip.hardEdge, }) : assert(semanticChildCount == null || semanticChildCount >= 0); /// {@template flutter.widgets.Scrollable.axisDirection} /// The direction in which this widget scrolls. /// /// For example, if the [Scrollable.axisDirection] is [AxisDirection.down], /// increasing the scroll position will cause content below the bottom of the /// viewport to become visible through the viewport. Similarly, if the /// axisDirection is [AxisDirection.right], increasing the scroll position /// will cause content beyond the right edge of the viewport to become visible /// through the viewport. /// /// Defaults to [AxisDirection.down]. /// {@endtemplate} final AxisDirection axisDirection; /// {@template flutter.widgets.Scrollable.controller} /// An object that can be used to control the position to which this widget is /// scrolled. /// /// A [ScrollController] serves several purposes. It can be used to control /// the initial scroll position (see [ScrollController.initialScrollOffset]). /// It can be used to control whether the scroll view should automatically /// save and restore its scroll position in the [PageStorage] (see /// [ScrollController.keepScrollOffset]). It can be used to read the current /// scroll position (see [ScrollController.offset]), or change it (see /// [ScrollController.animateTo]). /// /// If null, a [ScrollController] will be created internally by [Scrollable] /// in order to create and manage the [ScrollPosition]. /// /// See also: /// /// * [Scrollable.ensureVisible], which animates the scroll position to /// reveal a given [BuildContext]. /// {@endtemplate} final ScrollController? controller; /// {@template flutter.widgets.Scrollable.physics} /// How the widgets should respond to user input. /// /// For example, determines how the widget continues to animate after the /// user stops dragging the scroll view. /// /// Defaults to matching platform conventions via the physics provided from /// the ambient [ScrollConfiguration]. /// /// If an explicit [ScrollBehavior] is provided to /// [Scrollable.scrollBehavior], the [ScrollPhysics] provided by that behavior /// will take precedence after [Scrollable.physics]. /// /// The physics can be changed dynamically, but new physics will only take /// effect if the _class_ of the provided object changes. Merely constructing /// a new instance with a different configuration is insufficient to cause the /// physics to be reapplied. (This is because the final object used is /// generated dynamically, which can be relatively expensive, and it would be /// inefficient to speculatively create this object each frame to see if the /// physics should be updated.) /// /// See also: /// /// * [AlwaysScrollableScrollPhysics], which can be used to indicate that the /// scrollable should react to scroll requests (and possible overscroll) /// even if the scrollable's contents fit without scrolling being necessary. /// {@endtemplate} final ScrollPhysics? physics; /// Builds the viewport through which the scrollable content is displayed. /// /// A typical viewport uses the given [ViewportOffset] to determine which part /// of its content is actually visible through the viewport. /// /// See also: /// /// * [Viewport], which is a viewport that displays a list of slivers. /// * [ShrinkWrappingViewport], which is a viewport that displays a list of /// slivers and sizes itself based on the size of the slivers. final ViewportBuilder viewportBuilder; /// An optional function that will be called to calculate the distance to /// scroll when the scrollable is asked to scroll via the keyboard using a /// [ScrollAction]. /// /// If not supplied, the [Scrollable] will scroll a default amount when a /// keyboard navigation key is pressed (e.g. pageUp/pageDown, control-upArrow, /// etc.), or otherwise invoked by a [ScrollAction]. /// /// If [incrementCalculator] is null, the default for /// [ScrollIncrementType.page] is 80% of the size of the scroll window, and /// for [ScrollIncrementType.line], 50 logical pixels. final ScrollIncrementCalculator? incrementCalculator; /// Whether the scroll actions introduced by this [Scrollable] are exposed /// in the semantics tree. /// /// Text fields with an overflow are usually scrollable to make sure that the /// user can get to the beginning/end of the entered text. However, these /// scrolling actions are generally not exposed to the semantics layer. /// /// See also: /// /// * [GestureDetector.excludeFromSemantics], which is used to accomplish the /// exclusion. final bool excludeFromSemantics; /// The number of children that will contribute semantic information. /// /// The value will be null if the number of children is unknown or unbounded. /// /// Some subtypes of [ScrollView] can infer this value automatically. For /// example [ListView] will use the number of widgets in the child list, /// while the [ListView.separated] constructor will use half that amount. /// /// For [CustomScrollView] and other types which do not receive a builder /// or list of widgets, the child count must be explicitly provided. /// /// See also: /// /// * [CustomScrollView], for an explanation of scroll semantics. /// * [SemanticsConfiguration.scrollChildCount], the corresponding semantics property. final int? semanticChildCount; // TODO(jslavitz): Set the DragStartBehavior default to be start across all widgets. /// {@template flutter.widgets.scrollable.dragStartBehavior} /// Determines the way that drag start behavior is handled. /// /// If set to [DragStartBehavior.start], scrolling drag behavior will /// begin at the position where the drag gesture won the arena. If set to /// [DragStartBehavior.down] it will begin at the position where a down /// event is first detected. /// /// In general, setting this to [DragStartBehavior.start] will make drag /// animation smoother and setting it to [DragStartBehavior.down] will make /// drag behavior feel slightly more reactive. /// /// By default, the drag start behavior is [DragStartBehavior.start]. /// /// See also: /// /// * [DragGestureRecognizer.dragStartBehavior], which gives an example for /// the different behaviors. /// /// {@endtemplate} final DragStartBehavior dragStartBehavior; /// {@template flutter.widgets.scrollable.restorationId} /// Restoration ID to save and restore the scroll offset of the scrollable. /// /// If a restoration id is provided, the scrollable will persist its current /// scroll offset and restore it during state restoration. /// /// The scroll offset is persisted in a [RestorationBucket] claimed from /// the surrounding [RestorationScope] using the provided restoration ID. /// /// See also: /// /// * [RestorationManager], which explains how state restoration works in /// Flutter. /// {@endtemplate} final String? restorationId; /// {@macro flutter.widgets.shadow.scrollBehavior} /// /// [ScrollBehavior]s also provide [ScrollPhysics]. If an explicit /// [ScrollPhysics] is provided in [physics], it will take precedence, /// followed by [scrollBehavior], and then the inherited ancestor /// [ScrollBehavior]. final ScrollBehavior? scrollBehavior; /// {@macro flutter.material.Material.clipBehavior} /// /// Defaults to [Clip.hardEdge]. /// /// This is passed to decorators in [ScrollableDetails], and does not directly affect /// clipping of the [Scrollable]. This reflects the same [Clip] that is provided /// to [ScrollView.clipBehavior] and is supplied to the [Viewport]. final Clip clipBehavior; /// The axis along which the scroll view scrolls. /// /// Determined by the [axisDirection]. Axis get axis => axisDirectionToAxis(axisDirection); @override ScrollableState createState() => ScrollableState(); @override void debugFillProperties(DiagnosticPropertiesBuilder properties) { super.debugFillProperties(properties); properties.add(EnumProperty<AxisDirection>('axisDirection', axisDirection)); properties.add(DiagnosticsProperty<ScrollPhysics>('physics', physics)); properties.add(StringProperty('restorationId', restorationId)); } /// The state from the closest instance of this class that encloses the given /// context, or null if none is found. /// /// Typical usage is as follows: /// /// ```dart /// ScrollableState? scrollable = Scrollable.maybeOf(context); /// ``` /// /// Calling this method will create a dependency on the closest [Scrollable] /// in the [context], if there is one. /// /// See also: /// /// * [Scrollable.of], which is similar to this method, but asserts /// if no [Scrollable] ancestor is found. static ScrollableState? maybeOf(BuildContext context) { final _ScrollableScope? widget = context.dependOnInheritedWidgetOfExactType<_ScrollableScope>(); return widget?.scrollable; } /// The state from the closest instance of this class that encloses the given /// context. /// /// Typical usage is as follows: /// /// ```dart /// ScrollableState scrollable = Scrollable.of(context); /// ``` /// /// Calling this method will create a dependency on the closest [Scrollable] /// in the [context]. /// /// If no [Scrollable] ancestor is found, then this method will assert in /// debug mode, and throw an exception in release mode. /// /// See also: /// /// * [Scrollable.maybeOf], which is similar to this method, but returns null /// if no [Scrollable] ancestor is found. static ScrollableState of(BuildContext context) { final ScrollableState? scrollableState = maybeOf(context); assert(() { if (scrollableState == null) { throw FlutterError( 'Scrollable.of() was called with a context that does not contain a ' 'Scrollable widget.\n' 'No Scrollable widget ancestor could be found starting from the ' 'context that was passed to Scrollable.of(). This can happen ' 'because you are using a widget that looks for a Scrollable ' 'ancestor, but no such ancestor exists.\n' 'The context used was:\n' ' $context', ); } return true; }()); return scrollableState!; } /// Provides a heuristic to determine if expensive frame-bound tasks should be /// deferred for the [context] at a specific point in time. /// /// Calling this method does _not_ create a dependency on any other widget. /// This also means that the value returned is only good for the point in time /// when it is called, and callers will not get updated if the value changes. /// /// The heuristic used is determined by the [physics] of this [Scrollable] /// via [ScrollPhysics.recommendDeferredLoading]. That method is called with /// the current [ScrollPosition.activity]'s [ScrollActivity.velocity]. /// /// If there is no [Scrollable] in the widget tree above the [context], this /// method returns false. static bool recommendDeferredLoadingForContext(BuildContext context) { final _ScrollableScope? widget = context.getInheritedWidgetOfExactType<_ScrollableScope>(); if (widget == null) { return false; } return widget.position.recommendDeferredLoading(context); } /// Scrolls the scrollables that enclose the given context so as to make the /// given context visible. static Future<void> ensureVisible( BuildContext context, { double alignment = 0.0, Duration duration = Duration.zero, Curve curve = Curves.ease, ScrollPositionAlignmentPolicy alignmentPolicy = ScrollPositionAlignmentPolicy.explicit, }) { final List<Future<void>> futures = <Future<void>>[]; // The `targetRenderObject` is used to record the first target renderObject. // If there are multiple scrollable widgets nested, we should let // the `targetRenderObject` as visible as possible to improve the user experience. // Otherwise, let the outer renderObject as visible as possible maybe cause // the `targetRenderObject` invisible. // Also see https://github.com/flutter/flutter/issues/65100 RenderObject? targetRenderObject; ScrollableState? scrollable = Scrollable.maybeOf(context); while (scrollable != null) { futures.add(scrollable.position.ensureVisible( context.findRenderObject()!, alignment: alignment, duration: duration, curve: curve, alignmentPolicy: alignmentPolicy, targetRenderObject: targetRenderObject, )); targetRenderObject = targetRenderObject ?? context.findRenderObject(); context = scrollable.context; scrollable = Scrollable.maybeOf(context); } if (futures.isEmpty || duration == Duration.zero) { return Future<void>.value(); } if (futures.length == 1) { return futures.single; } return Future.wait<void>(futures).then<void>((List<void> _) => null); } } // Enable Scrollable.of() to work as if ScrollableState was an inherited widget. // ScrollableState.build() always rebuilds its _ScrollableScope. class _ScrollableScope extends InheritedWidget { const _ScrollableScope({ required this.scrollable, required this.position, required super.child, }); final ScrollableState scrollable; final ScrollPosition position; @override bool updateShouldNotify(_ScrollableScope old) { return position != old.position; } } /// State object for a [Scrollable] widget. /// /// To manipulate a [Scrollable] widget's scroll position, use the object /// obtained from the [position] property. /// /// To be informed of when a [Scrollable] widget is scrolling, use a /// [NotificationListener] to listen for [ScrollNotification] notifications. /// /// This class is not intended to be subclassed. To specialize the behavior of a /// [Scrollable], provide it with a [ScrollPhysics]. class ScrollableState extends State<Scrollable> with TickerProviderStateMixin, RestorationMixin implements ScrollContext { // GETTERS /// The manager for this [Scrollable] widget's viewport position. /// /// To control what kind of [ScrollPosition] is created for a [Scrollable], /// provide it with custom [ScrollController] that creates the appropriate /// [ScrollPosition] in its [ScrollController.createScrollPosition] method. ScrollPosition get position => _position!; ScrollPosition? _position; /// The resolved [ScrollPhysics] of the [ScrollableState]. ScrollPhysics? get resolvedPhysics => _physics; ScrollPhysics? _physics; /// An [Offset] that represents the absolute distance from the origin, or 0, /// of the [ScrollPosition] expressed in the associated [Axis]. /// /// Used by [EdgeDraggingAutoScroller] to progress the position forward when a /// drag gesture reaches the edge of the [Viewport]. Offset get deltaToScrollOrigin { switch (axisDirection) { case AxisDirection.down: return Offset(0, position.pixels); case AxisDirection.up: return Offset(0, -position.pixels); case AxisDirection.left: return Offset(-position.pixels, 0); case AxisDirection.right: return Offset(position.pixels, 0); } } ScrollController get _effectiveScrollController => widget.controller ?? _fallbackScrollController!; @override AxisDirection get axisDirection => widget.axisDirection; @override TickerProvider get vsync => this; @override BuildContext? get notificationContext => _gestureDetectorKey.currentContext; @override BuildContext get storageContext => context; @override String? get restorationId => widget.restorationId; final _RestorableScrollOffset _persistedScrollOffset = _RestorableScrollOffset(); late ScrollBehavior _configuration; ScrollController? _fallbackScrollController; DeviceGestureSettings? _mediaQueryGestureSettings; // Only call this from places that will definitely trigger a rebuild. void _updatePosition() { _configuration = widget.scrollBehavior ?? ScrollConfiguration.of(context); _physics = _configuration.getScrollPhysics(context); if (widget.physics != null) { _physics = widget.physics!.applyTo(_physics); } else if (widget.scrollBehavior != null) { _physics = widget.scrollBehavior!.getScrollPhysics(context).applyTo(_physics); } final ScrollPosition? oldPosition = _position; if (oldPosition != null) { _effectiveScrollController.detach(oldPosition); // It's important that we not dispose the old position until after the // viewport has had a chance to unregister its listeners from the old // position. So, schedule a microtask to do it. scheduleMicrotask(oldPosition.dispose); } _position = _effectiveScrollController.createScrollPosition(_physics!, this, oldPosition); assert(_position != null); _effectiveScrollController.attach(position); } @override void restoreState(RestorationBucket? oldBucket, bool initialRestore) { registerForRestoration(_persistedScrollOffset, 'offset'); assert(_position != null); if (_persistedScrollOffset.value != null) { position.restoreOffset(_persistedScrollOffset.value!, initialRestore: initialRestore); } } @override void saveOffset(double offset) { assert(debugIsSerializableForRestoration(offset)); _persistedScrollOffset.value = offset; // [saveOffset] is called after a scrolling ends and it is usually not // followed by a frame. Therefore, manually flush restoration data. ServicesBinding.instance.restorationManager.flushData(); } @override void initState() { if (widget.controller == null) { _fallbackScrollController = ScrollController(); } super.initState(); } @override void didChangeDependencies() { _mediaQueryGestureSettings = MediaQuery.maybeGestureSettingsOf(context); _updatePosition(); super.didChangeDependencies(); } bool _shouldUpdatePosition(Scrollable oldWidget) { ScrollPhysics? newPhysics = widget.physics ?? widget.scrollBehavior?.getScrollPhysics(context); ScrollPhysics? oldPhysics = oldWidget.physics ?? oldWidget.scrollBehavior?.getScrollPhysics(context); do { if (newPhysics?.runtimeType != oldPhysics?.runtimeType) { return true; } newPhysics = newPhysics?.parent; oldPhysics = oldPhysics?.parent; } while (newPhysics != null || oldPhysics != null); return widget.controller?.runtimeType != oldWidget.controller?.runtimeType; } @override void didUpdateWidget(Scrollable oldWidget) { super.didUpdateWidget(oldWidget); if (widget.controller != oldWidget.controller) { if (oldWidget.controller == null) { // The old controller was null, meaning the fallback cannot be null. // Dispose of the fallback. assert(_fallbackScrollController != null); assert(widget.controller != null); _fallbackScrollController!.detach(position); _fallbackScrollController!.dispose(); _fallbackScrollController = null; } else { // The old controller was not null, detach. oldWidget.controller?.detach(position); if (widget.controller == null) { // If the new controller is null, we need to set up the fallback // ScrollController. _fallbackScrollController = ScrollController(); } } // Attach the updated effective scroll controller. _effectiveScrollController.attach(position); } if (_shouldUpdatePosition(oldWidget)) { _updatePosition(); } } @override void dispose() { if (widget.controller != null) { widget.controller!.detach(position); } else { _fallbackScrollController?.detach(position); _fallbackScrollController?.dispose(); } position.dispose(); _persistedScrollOffset.dispose(); super.dispose(); } // SEMANTICS final GlobalKey _scrollSemanticsKey = GlobalKey(); @override @protected void setSemanticsActions(Set<SemanticsAction> actions) { if (_gestureDetectorKey.currentState != null) { _gestureDetectorKey.currentState!.replaceSemanticsActions(actions); } } // GESTURE RECOGNITION AND POINTER IGNORING final GlobalKey<RawGestureDetectorState> _gestureDetectorKey = GlobalKey<RawGestureDetectorState>(); final GlobalKey _ignorePointerKey = GlobalKey(); // This field is set during layout, and then reused until the next time it is set. Map<Type, GestureRecognizerFactory> _gestureRecognizers = const <Type, GestureRecognizerFactory>{}; bool _shouldIgnorePointer = false; bool? _lastCanDrag; Axis? _lastAxisDirection; @override @protected void setCanDrag(bool value) { if (value == _lastCanDrag && (!value || widget.axis == _lastAxisDirection)) { return; } if (!value) { _gestureRecognizers = const <Type, GestureRecognizerFactory>{}; // Cancel the active hold/drag (if any) because the gesture recognizers // will soon be disposed by our RawGestureDetector, and we won't be // receiving pointer up events to cancel the hold/drag. _handleDragCancel(); } else { switch (widget.axis) { case Axis.vertical: _gestureRecognizers = <Type, GestureRecognizerFactory>{ VerticalDragGestureRecognizer: GestureRecognizerFactoryWithHandlers<VerticalDragGestureRecognizer>( () => VerticalDragGestureRecognizer(supportedDevices: _configuration.dragDevices), (VerticalDragGestureRecognizer instance) { instance ..onDown = _handleDragDown ..onStart = _handleDragStart ..onUpdate = _handleDragUpdate ..onEnd = _handleDragEnd ..onCancel = _handleDragCancel ..minFlingDistance = _physics?.minFlingDistance ..minFlingVelocity = _physics?.minFlingVelocity ..maxFlingVelocity = _physics?.maxFlingVelocity ..velocityTrackerBuilder = _configuration.velocityTrackerBuilder(context) ..dragStartBehavior = widget.dragStartBehavior ..gestureSettings = _mediaQueryGestureSettings ..supportedDevices = _configuration.dragDevices; }, ), }; case Axis.horizontal: _gestureRecognizers = <Type, GestureRecognizerFactory>{ HorizontalDragGestureRecognizer: GestureRecognizerFactoryWithHandlers<HorizontalDragGestureRecognizer>( () => HorizontalDragGestureRecognizer(supportedDevices: _configuration.dragDevices), (HorizontalDragGestureRecognizer instance) { instance ..onDown = _handleDragDown ..onStart = _handleDragStart ..onUpdate = _handleDragUpdate ..onEnd = _handleDragEnd ..onCancel = _handleDragCancel ..minFlingDistance = _physics?.minFlingDistance ..minFlingVelocity = _physics?.minFlingVelocity ..maxFlingVelocity = _physics?.maxFlingVelocity ..velocityTrackerBuilder = _configuration.velocityTrackerBuilder(context) ..dragStartBehavior = widget.dragStartBehavior ..gestureSettings = _mediaQueryGestureSettings ..supportedDevices = _configuration.dragDevices; }, ), }; } } _lastCanDrag = value; _lastAxisDirection = widget.axis; if (_gestureDetectorKey.currentState != null) { _gestureDetectorKey.currentState!.replaceGestureRecognizers(_gestureRecognizers); } } @override @protected void setIgnorePointer(bool value) { if (_shouldIgnorePointer == value) { return; } _shouldIgnorePointer = value; if (_ignorePointerKey.currentContext != null) { final RenderIgnorePointer renderBox = _ignorePointerKey.currentContext!.findRenderObject()! as RenderIgnorePointer; renderBox.ignoring = _shouldIgnorePointer; } } // TOUCH HANDLERS Drag? _drag; ScrollHoldController? _hold; void _handleDragDown(DragDownDetails details) { assert(_drag == null); assert(_hold == null); _hold = position.hold(_disposeHold); } void _handleDragStart(DragStartDetails details) { // It's possible for _hold to become null between _handleDragDown and // _handleDragStart, for example if some user code calls jumpTo or otherwise // triggers a new activity to begin. assert(_drag == null); _drag = position.drag(details, _disposeDrag); assert(_drag != null); assert(_hold == null); } void _handleDragUpdate(DragUpdateDetails details) { // _drag might be null if the drag activity ended and called _disposeDrag. assert(_hold == null || _drag == null); _drag?.update(details); } void _handleDragEnd(DragEndDetails details) { // _drag might be null if the drag activity ended and called _disposeDrag. assert(_hold == null || _drag == null); _drag?.end(details); assert(_drag == null); } void _handleDragCancel() { if (_gestureDetectorKey.currentContext == null) { // The cancel was caused by the GestureDetector getting disposed, which // means we will get disposed momentarily as well and shouldn't do // any work. return; } // _hold might be null if the drag started. // _drag might be null if the drag activity ended and called _disposeDrag. assert(_hold == null || _drag == null); _hold?.cancel(); _drag?.cancel(); assert(_hold == null); assert(_drag == null); } void _disposeHold() { _hold = null; } void _disposeDrag() { _drag = null; } // SCROLL WHEEL // Returns the offset that should result from applying [event] to the current // position, taking min/max scroll extent into account. double _targetScrollOffsetForPointerScroll(double delta) { return math.min( math.max(position.pixels + delta, position.minScrollExtent), position.maxScrollExtent, ); } // Returns the delta that should result from applying [event] with axis, // direction, and any modifiers specified by the ScrollBehavior taken into // account. double _pointerSignalEventDelta(PointerScrollEvent event) { late double delta; final Set<LogicalKeyboardKey> pressed = HardwareKeyboard.instance.logicalKeysPressed; final bool flipAxes = pressed.any(_configuration.pointerAxisModifiers.contains) && // Axes are only flipped for physical mouse wheel input. // On some platforms, like web, trackpad input is handled through pointer // signals, but should not be included in this axis modifying behavior. // This is because on a trackpad, all directional axes are available to // the user, while mouse scroll wheels typically are restricted to one // axis. event.kind == PointerDeviceKind.mouse; switch (widget.axis) { case Axis.horizontal: delta = flipAxes ? event.scrollDelta.dy : event.scrollDelta.dx; case Axis.vertical: delta = flipAxes ? event.scrollDelta.dx : event.scrollDelta.dy; } if (axisDirectionIsReversed(widget.axisDirection)) { delta *= -1; } return delta; } void _receivedPointerSignal(PointerSignalEvent event) { if (event is PointerScrollEvent && _position != null) { if (_physics != null && !_physics!.shouldAcceptUserOffset(position)) { return; } final double delta = _pointerSignalEventDelta(event); final double targetScrollOffset = _targetScrollOffsetForPointerScroll(delta); // Only express interest in the event if it would actually result in a scroll. if (delta != 0.0 && targetScrollOffset != position.pixels) { GestureBinding.instance.pointerSignalResolver.register(event, _handlePointerScroll); } } else if (event is PointerScrollInertiaCancelEvent) { position.pointerScroll(0); // Don't use the pointer signal resolver, all hit-tested scrollables should stop. } } void _handlePointerScroll(PointerEvent event) { assert(event is PointerScrollEvent); final double delta = _pointerSignalEventDelta(event as PointerScrollEvent); final double targetScrollOffset = _targetScrollOffsetForPointerScroll(delta); if (delta != 0.0 && targetScrollOffset != position.pixels) { position.pointerScroll(delta); } } bool _handleScrollMetricsNotification(ScrollMetricsNotification notification) { if (notification.depth == 0) { final RenderObject? scrollSemanticsRenderObject = _scrollSemanticsKey.currentContext?.findRenderObject(); if (scrollSemanticsRenderObject != null) { scrollSemanticsRenderObject.markNeedsSemanticsUpdate(); } } return false; } // DESCRIPTION @override Widget build(BuildContext context) { assert(_position != null); // _ScrollableScope must be placed above the BuildContext returned by notificationContext // so that we can get this ScrollableState by doing the following: // // ScrollNotification notification; // Scrollable.of(notification.context) // // Since notificationContext is pointing to _gestureDetectorKey.context, _ScrollableScope // must be placed above the widget using it: RawGestureDetector Widget result = _ScrollableScope( scrollable: this, position: position, // TODO(ianh): Having all these global keys is sad. child: Listener( onPointerSignal: _receivedPointerSignal, child: RawGestureDetector( key: _gestureDetectorKey, gestures: _gestureRecognizers, behavior: HitTestBehavior.opaque, excludeFromSemantics: widget.excludeFromSemantics, child: Semantics( explicitChildNodes: !widget.excludeFromSemantics, child: IgnorePointer( key: _ignorePointerKey, ignoring: _shouldIgnorePointer, ignoringSemantics: false, child: widget.viewportBuilder(context, position), ), ), ), ), ); if (!widget.excludeFromSemantics) { result = NotificationListener<ScrollMetricsNotification>( onNotification: _handleScrollMetricsNotification, child: _ScrollSemantics( key: _scrollSemanticsKey, position: position, allowImplicitScrolling: _physics!.allowImplicitScrolling, semanticChildCount: widget.semanticChildCount, child: result, ) ); } final ScrollableDetails details = ScrollableDetails( direction: widget.axisDirection, controller: _effectiveScrollController, decorationClipBehavior: widget.clipBehavior, ); result = _configuration.buildScrollbar( context, _configuration.buildOverscrollIndicator(context, result, details), details, ); // Selection is only enabled when there is a parent registrar. final SelectionRegistrar? registrar = SelectionContainer.maybeOf(context); if (registrar != null) { result = _ScrollableSelectionHandler( state: this, position: position, registrar: registrar, child: result, ); } return result; } @override void debugFillProperties(DiagnosticPropertiesBuilder properties) { super.debugFillProperties(properties); properties.add(DiagnosticsProperty<ScrollPosition>('position', position)); properties.add(DiagnosticsProperty<ScrollPhysics>('effective physics', _physics)); } } /// A widget to handle selection for a scrollable. /// /// This widget registers itself to the [registrar] and uses /// [SelectionContainer] to collect selectables from its subtree. class _ScrollableSelectionHandler extends StatefulWidget { const _ScrollableSelectionHandler({ required this.state, required this.position, required this.registrar, required this.child, }); final ScrollableState state; final ScrollPosition position; final Widget child; final SelectionRegistrar registrar; @override _ScrollableSelectionHandlerState createState() => _ScrollableSelectionHandlerState(); } class _ScrollableSelectionHandlerState extends State<_ScrollableSelectionHandler> { late _ScrollableSelectionContainerDelegate _selectionDelegate; @override void initState() { super.initState(); _selectionDelegate = _ScrollableSelectionContainerDelegate( state: widget.state, position: widget.position, ); } @override void didUpdateWidget(_ScrollableSelectionHandler oldWidget) { super.didUpdateWidget(oldWidget); if (oldWidget.position != widget.position) { _selectionDelegate.position = widget.position; } } @override void dispose() { _selectionDelegate.dispose(); super.dispose(); } @override Widget build(BuildContext context) { return SelectionContainer( registrar: widget.registrar, delegate: _selectionDelegate, child: widget.child, ); } } /// This updater handles the case where the selectables change frequently, and /// it optimizes toward scrolling updates. /// /// It keeps track of the drag start offset relative to scroll origin for every /// selectable. The records are used to determine whether the selection is up to /// date with the scroll position when it sends the drag update event to a /// selectable. class _ScrollableSelectionContainerDelegate extends MultiSelectableSelectionContainerDelegate { _ScrollableSelectionContainerDelegate({ required this.state, required ScrollPosition position }) : _position = position, _autoScroller = EdgeDraggingAutoScroller(state, velocityScalar: _kDefaultSelectToScrollVelocityScalar) { _position.addListener(_scheduleLayoutChange); } // Pointer drag is a single point, it should not have a size. static const double _kDefaultDragTargetSize = 0; // An eye-balled value for a smooth scrolling speed. static const double _kDefaultSelectToScrollVelocityScalar = 30; final ScrollableState state; final EdgeDraggingAutoScroller _autoScroller; bool _scheduledLayoutChange = false; Offset? _currentDragStartRelatedToOrigin; Offset? _currentDragEndRelatedToOrigin; // The scrollable only auto scrolls if the selection starts in the scrollable. bool _selectionStartsInScrollable = false; ScrollPosition get position => _position; ScrollPosition _position; set position(ScrollPosition other) { if (other == _position) { return; } _position.removeListener(_scheduleLayoutChange); _position = other; _position.addListener(_scheduleLayoutChange); } // The layout will only be updated a frame later than position changes. // Schedule PostFrameCallback to capture the accurate layout. void _scheduleLayoutChange() { if (_scheduledLayoutChange) { return; } _scheduledLayoutChange = true; SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) { if (!_scheduledLayoutChange) { return; } _scheduledLayoutChange = false; layoutDidChange(); }); } /// Stores the scroll offset when a scrollable receives the last /// [SelectionEdgeUpdateEvent]. /// /// The stored scroll offset may be null if a scrollable never receives a /// [SelectionEdgeUpdateEvent]. /// /// When a new [SelectionEdgeUpdateEvent] is dispatched to a selectable, this /// updater checks the current scroll offset against the one stored in these /// records. If the scroll offset is different, it synthesizes an opposite /// [SelectionEdgeUpdateEvent] and dispatches the event before dispatching the /// new event. /// /// For example, if a selectable receives an end [SelectionEdgeUpdateEvent] /// and its scroll offset in the records is different from the current value, /// it synthesizes a start [SelectionEdgeUpdateEvent] and dispatches it before /// dispatching the original end [SelectionEdgeUpdateEvent]. final Map<Selectable, double> _selectableStartEdgeUpdateRecords = <Selectable, double>{}; final Map<Selectable, double> _selectableEndEdgeUpdateRecords = <Selectable, double>{}; @override void didChangeSelectables() { final Set<Selectable> selectableSet = selectables.toSet(); _selectableStartEdgeUpdateRecords.removeWhere((Selectable key, double value) => !selectableSet.contains(key)); _selectableEndEdgeUpdateRecords.removeWhere((Selectable key, double value) => !selectableSet.contains(key)); super.didChangeSelectables(); } @override SelectionResult handleClearSelection(ClearSelectionEvent event) { _selectableStartEdgeUpdateRecords.clear(); _selectableEndEdgeUpdateRecords.clear(); _currentDragStartRelatedToOrigin = null; _currentDragEndRelatedToOrigin = null; _selectionStartsInScrollable = false; return super.handleClearSelection(event); } @override SelectionResult handleSelectionEdgeUpdate(SelectionEdgeUpdateEvent event) { if (_currentDragEndRelatedToOrigin == null && _currentDragStartRelatedToOrigin == null) { assert(!_selectionStartsInScrollable); _selectionStartsInScrollable = _globalPositionInScrollable(event.globalPosition); } final Offset deltaToOrigin = _getDeltaToScrollOrigin(state); if (event.type == SelectionEventType.endEdgeUpdate) { _currentDragEndRelatedToOrigin = _inferPositionRelatedToOrigin(event.globalPosition); final Offset endOffset = _currentDragEndRelatedToOrigin!.translate(-deltaToOrigin.dx, -deltaToOrigin.dy); event = SelectionEdgeUpdateEvent.forEnd(globalPosition: endOffset); } else { _currentDragStartRelatedToOrigin = _inferPositionRelatedToOrigin(event.globalPosition); final Offset startOffset = _currentDragStartRelatedToOrigin!.translate(-deltaToOrigin.dx, -deltaToOrigin.dy); event = SelectionEdgeUpdateEvent.forStart(globalPosition: startOffset); } final SelectionResult result = super.handleSelectionEdgeUpdate(event); // Result may be pending if one of the selectable child is also a scrollable. // In that case, the parent scrollable needs to wait for the child to finish // scrolling. if (result == SelectionResult.pending) { _autoScroller.stopAutoScroll(); return result; } if (_selectionStartsInScrollable) { _autoScroller.startAutoScrollIfNecessary(_dragTargetFromEvent(event)); if (_autoScroller.scrolling) { return SelectionResult.pending; } } return result; } Offset _inferPositionRelatedToOrigin(Offset globalPosition) { final RenderBox box = state.context.findRenderObject()! as RenderBox; final Offset localPosition = box.globalToLocal(globalPosition); if (!_selectionStartsInScrollable) { // If the selection starts outside of the scrollable, selecting across the // scrollable boundary will act as selecting the entire content in the // scrollable. This logic move the offset to the 0.0 or infinity to cover // the entire content if the input position is outside of the scrollable. if (localPosition.dy < 0 || localPosition.dx < 0) { return box.localToGlobal(Offset.zero); } if (localPosition.dy > box.size.height || localPosition.dx > box.size.width) { return Offset.infinite; } } final Offset deltaToOrigin = _getDeltaToScrollOrigin(state); return box.localToGlobal(localPosition.translate(deltaToOrigin.dx, deltaToOrigin.dy)); } /// Infers the [_currentDragStartRelatedToOrigin] and /// [_currentDragEndRelatedToOrigin] from the geometry. /// /// This method is called after a select word and select all event where the /// selection is triggered by none drag events. The /// [_currentDragStartRelatedToOrigin] and [_currentDragEndRelatedToOrigin] /// are essential to handle future [SelectionEdgeUpdateEvent]s. void _updateDragLocationsFromGeometries({bool forceUpdateStart = true, bool forceUpdateEnd = true}) { final Offset deltaToOrigin = _getDeltaToScrollOrigin(state); final RenderBox box = state.context.findRenderObject()! as RenderBox; final Matrix4 transform = box.getTransformTo(null); if (currentSelectionStartIndex != -1 && (_currentDragStartRelatedToOrigin == null || forceUpdateStart)) { final SelectionGeometry geometry = selectables[currentSelectionStartIndex].value; assert(geometry.hasSelection); final SelectionPoint start = geometry.startSelectionPoint!; final Matrix4 childTransform = selectables[currentSelectionStartIndex].getTransformTo(box); final Offset localDragStart = MatrixUtils.transformPoint( childTransform, start.localPosition + Offset(0, - start.lineHeight / 2), ); _currentDragStartRelatedToOrigin = MatrixUtils.transformPoint(transform, localDragStart + deltaToOrigin); } if (currentSelectionEndIndex != -1 && (_currentDragEndRelatedToOrigin == null || forceUpdateEnd)) { final SelectionGeometry geometry = selectables[currentSelectionEndIndex].value; assert(geometry.hasSelection); final SelectionPoint end = geometry.endSelectionPoint!; final Matrix4 childTransform = selectables[currentSelectionEndIndex].getTransformTo(box); final Offset localDragEnd = MatrixUtils.transformPoint( childTransform, end.localPosition + Offset(0, - end.lineHeight / 2), ); _currentDragEndRelatedToOrigin = MatrixUtils.transformPoint(transform, localDragEnd + deltaToOrigin); } } @override SelectionResult handleSelectAll(SelectAllSelectionEvent event) { assert(!_selectionStartsInScrollable); final SelectionResult result = super.handleSelectAll(event); assert((currentSelectionStartIndex == -1) == (currentSelectionEndIndex == -1)); if (currentSelectionStartIndex != -1) { _updateDragLocationsFromGeometries(); } return result; } @override SelectionResult handleSelectWord(SelectWordSelectionEvent event) { _selectionStartsInScrollable = _globalPositionInScrollable(event.globalPosition); final SelectionResult result = super.handleSelectWord(event); _updateDragLocationsFromGeometries(); return result; } @override SelectionResult handleGranularlyExtendSelection(GranularlyExtendSelectionEvent event) { final SelectionResult result = super.handleGranularlyExtendSelection(event); // The selection geometry may not have the accurate offset for the edges // that are outside of the viewport whose transform may not be valid. Only // the edge this event is updating is sure to be accurate. _updateDragLocationsFromGeometries( forceUpdateStart: !event.isEnd, forceUpdateEnd: event.isEnd, ); if (_selectionStartsInScrollable) { _jumpToEdge(event.isEnd); } return result; } @override SelectionResult handleDirectionallyExtendSelection(DirectionallyExtendSelectionEvent event) { final SelectionResult result = super.handleDirectionallyExtendSelection(event); // The selection geometry may not have the accurate offset for the edges // that are outside of the viewport whose transform may not be valid. Only // the edge this event is updating is sure to be accurate. _updateDragLocationsFromGeometries( forceUpdateStart: !event.isEnd, forceUpdateEnd: event.isEnd, ); if (_selectionStartsInScrollable) { _jumpToEdge(event.isEnd); } return result; } void _jumpToEdge(bool isExtent) { final Selectable selectable; final double? lineHeight; final SelectionPoint? edge; if (isExtent) { selectable = selectables[currentSelectionEndIndex]; edge = selectable.value.endSelectionPoint; lineHeight = selectable.value.endSelectionPoint!.lineHeight; } else { selectable = selectables[currentSelectionStartIndex]; edge = selectable.value.startSelectionPoint; lineHeight = selectable.value.startSelectionPoint?.lineHeight; } if (lineHeight == null || edge == null) { return; } final RenderBox scrollableBox = state.context.findRenderObject()! as RenderBox; final Matrix4 transform = selectable.getTransformTo(scrollableBox); final Offset edgeOffsetInScrollableCoordinates = MatrixUtils.transformPoint(transform, edge.localPosition); final Rect scrollableRect = Rect.fromLTRB(0, 0, scrollableBox.size.width, scrollableBox.size.height); switch (state.axisDirection) { case AxisDirection.up: final double edgeBottom = edgeOffsetInScrollableCoordinates.dy; final double edgeTop = edgeOffsetInScrollableCoordinates.dy - lineHeight; if (edgeBottom >= scrollableRect.bottom && edgeTop <= scrollableRect.top) { return; } if (edgeBottom > scrollableRect.bottom) { position.jumpTo(position.pixels + scrollableRect.bottom - edgeBottom); return; } if (edgeTop < scrollableRect.top) { position.jumpTo(position.pixels + scrollableRect.top - edgeTop); } return; case AxisDirection.right: final double edge = edgeOffsetInScrollableCoordinates.dx; if (edge >= scrollableRect.right && edge <= scrollableRect.left) { return; } if (edge > scrollableRect.right) { position.jumpTo(position.pixels + edge - scrollableRect.right); return; } if (edge < scrollableRect.left) { position.jumpTo(position.pixels + edge - scrollableRect.left); } return; case AxisDirection.down: final double edgeBottom = edgeOffsetInScrollableCoordinates.dy; final double edgeTop = edgeOffsetInScrollableCoordinates.dy - lineHeight; if (edgeBottom >= scrollableRect.bottom && edgeTop <= scrollableRect.top) { return; } if (edgeBottom > scrollableRect.bottom) { position.jumpTo(position.pixels + edgeBottom - scrollableRect.bottom); return; } if (edgeTop < scrollableRect.top) { position.jumpTo(position.pixels + edgeTop - scrollableRect.top); } return; case AxisDirection.left: final double edge = edgeOffsetInScrollableCoordinates.dx; if (edge >= scrollableRect.right && edge <= scrollableRect.left) { return; } if (edge > scrollableRect.right) { position.jumpTo(position.pixels + scrollableRect.right - edge); return; } if (edge < scrollableRect.left) { position.jumpTo(position.pixels + scrollableRect.left - edge); } return; } } bool _globalPositionInScrollable(Offset globalPosition) { final RenderBox box = state.context.findRenderObject()! as RenderBox; final Offset localPosition = box.globalToLocal(globalPosition); final Rect rect = Rect.fromLTWH(0, 0, box.size.width, box.size.height); return rect.contains(localPosition); } Rect _dragTargetFromEvent(SelectionEdgeUpdateEvent event) { return Rect.fromCenter(center: event.globalPosition, width: _kDefaultDragTargetSize, height: _kDefaultDragTargetSize); } @override SelectionResult dispatchSelectionEventToChild(Selectable selectable, SelectionEvent event) { switch (event.type) { case SelectionEventType.startEdgeUpdate: _selectableStartEdgeUpdateRecords[selectable] = state.position.pixels; ensureChildUpdated(selectable); case SelectionEventType.endEdgeUpdate: _selectableEndEdgeUpdateRecords[selectable] = state.position.pixels; ensureChildUpdated(selectable); case SelectionEventType.granularlyExtendSelection: case SelectionEventType.directionallyExtendSelection: ensureChildUpdated(selectable); _selectableStartEdgeUpdateRecords[selectable] = state.position.pixels; _selectableEndEdgeUpdateRecords[selectable] = state.position.pixels; case SelectionEventType.clear: _selectableEndEdgeUpdateRecords.remove(selectable); _selectableStartEdgeUpdateRecords.remove(selectable); case SelectionEventType.selectAll: case SelectionEventType.selectWord: _selectableEndEdgeUpdateRecords[selectable] = state.position.pixels; _selectableStartEdgeUpdateRecords[selectable] = state.position.pixels; } return super.dispatchSelectionEventToChild(selectable, event); } @override void ensureChildUpdated(Selectable selectable) { final double newRecord = state.position.pixels; final double? previousStartRecord = _selectableStartEdgeUpdateRecords[selectable]; if (_currentDragStartRelatedToOrigin != null && (previousStartRecord == null || (newRecord - previousStartRecord).abs() > precisionErrorTolerance)) { // Make sure the selectable has up to date events. final Offset deltaToOrigin = _getDeltaToScrollOrigin(state); final Offset startOffset = _currentDragStartRelatedToOrigin!.translate(-deltaToOrigin.dx, -deltaToOrigin.dy); selectable.dispatchSelectionEvent(SelectionEdgeUpdateEvent.forStart(globalPosition: startOffset)); } final double? previousEndRecord = _selectableEndEdgeUpdateRecords[selectable]; if (_currentDragEndRelatedToOrigin != null && (previousEndRecord == null || (newRecord - previousEndRecord).abs() > precisionErrorTolerance)) { // Make sure the selectable has up to date events. final Offset deltaToOrigin = _getDeltaToScrollOrigin(state); final Offset endOffset = _currentDragEndRelatedToOrigin!.translate(-deltaToOrigin.dx, -deltaToOrigin.dy); selectable.dispatchSelectionEvent(SelectionEdgeUpdateEvent.forEnd(globalPosition: endOffset)); } } @override void dispose() { _selectableStartEdgeUpdateRecords.clear(); _selectableEndEdgeUpdateRecords.clear(); _scheduledLayoutChange = false; _autoScroller.stopAutoScroll(); super.dispose(); } } Offset _getDeltaToScrollOrigin(ScrollableState scrollableState) { switch (scrollableState.axisDirection) { case AxisDirection.down: return Offset(0, scrollableState.position.pixels); case AxisDirection.up: return Offset(0, -scrollableState.position.pixels); case AxisDirection.left: return Offset(-scrollableState.position.pixels, 0); case AxisDirection.right: return Offset(scrollableState.position.pixels, 0); } } /// With [_ScrollSemantics] certain child [SemanticsNode]s can be /// excluded from the scrollable area for semantics purposes. /// /// Nodes, that are to be excluded, have to be tagged with /// [RenderViewport.excludeFromScrolling] and the [RenderAbstractViewport] in /// use has to add the [RenderViewport.useTwoPaneSemantics] tag to its /// [SemanticsConfiguration] by overriding /// [RenderObject.describeSemanticsConfiguration]. /// /// If the tag [RenderViewport.useTwoPaneSemantics] is present on the viewport, /// two semantics nodes will be used to represent the [Scrollable]: The outer /// node will contain all children, that are excluded from scrolling. The inner /// node, which is annotated with the scrolling actions, will house the /// scrollable children. class _ScrollSemantics extends SingleChildRenderObjectWidget { const _ScrollSemantics({ super.key, required this.position, required this.allowImplicitScrolling, required this.semanticChildCount, super.child, }) : assert(semanticChildCount == null || semanticChildCount >= 0); final ScrollPosition position; final bool allowImplicitScrolling; final int? semanticChildCount; @override _RenderScrollSemantics createRenderObject(BuildContext context) { return _RenderScrollSemantics( position: position, allowImplicitScrolling: allowImplicitScrolling, semanticChildCount: semanticChildCount, ); } @override void updateRenderObject(BuildContext context, _RenderScrollSemantics renderObject) { renderObject ..allowImplicitScrolling = allowImplicitScrolling ..position = position ..semanticChildCount = semanticChildCount; } } class _RenderScrollSemantics extends RenderProxyBox { _RenderScrollSemantics({ required ScrollPosition position, required bool allowImplicitScrolling, required int? semanticChildCount, RenderBox? child, }) : _position = position, _allowImplicitScrolling = allowImplicitScrolling, _semanticChildCount = semanticChildCount, super(child) { position.addListener(markNeedsSemanticsUpdate); } /// Whether this render object is excluded from the semantic tree. ScrollPosition get position => _position; ScrollPosition _position; set position(ScrollPosition value) { if (value == _position) { return; } _position.removeListener(markNeedsSemanticsUpdate); _position = value; _position.addListener(markNeedsSemanticsUpdate); markNeedsSemanticsUpdate(); } /// Whether this node can be scrolled implicitly. bool get allowImplicitScrolling => _allowImplicitScrolling; bool _allowImplicitScrolling; set allowImplicitScrolling(bool value) { if (value == _allowImplicitScrolling) { return; } _allowImplicitScrolling = value; markNeedsSemanticsUpdate(); } int? get semanticChildCount => _semanticChildCount; int? _semanticChildCount; set semanticChildCount(int? value) { if (value == semanticChildCount) { return; } _semanticChildCount = value; markNeedsSemanticsUpdate(); } @override void describeSemanticsConfiguration(SemanticsConfiguration config) { super.describeSemanticsConfiguration(config); config.isSemanticBoundary = true; if (position.haveDimensions) { config ..hasImplicitScrolling = allowImplicitScrolling ..scrollPosition = _position.pixels ..scrollExtentMax = _position.maxScrollExtent ..scrollExtentMin = _position.minScrollExtent ..scrollChildCount = semanticChildCount; } } SemanticsNode? _innerNode; @override void assembleSemanticsNode(SemanticsNode node, SemanticsConfiguration config, Iterable<SemanticsNode> children) { if (children.isEmpty || !children.first.isTagged(RenderViewport.useTwoPaneSemantics)) { _innerNode = null; super.assembleSemanticsNode(node, config, children); return; } _innerNode ??= SemanticsNode(showOnScreen: showOnScreen); _innerNode! ..isMergedIntoParent = node.isPartOfNodeMerging ..rect = node.rect; int? firstVisibleIndex; final List<SemanticsNode> excluded = <SemanticsNode>[_innerNode!]; final List<SemanticsNode> included = <SemanticsNode>[]; for (final SemanticsNode child in children) { assert(child.isTagged(RenderViewport.useTwoPaneSemantics)); if (child.isTagged(RenderViewport.excludeFromScrolling)) { excluded.add(child); } else { if (!child.hasFlag(SemanticsFlag.isHidden)) { firstVisibleIndex ??= child.indexInParent; } included.add(child); } } config.scrollIndex = firstVisibleIndex; node.updateWith(config: null, childrenInInversePaintOrder: excluded); _innerNode!.updateWith(config: config, childrenInInversePaintOrder: included); } @override void clearSemantics() { super.clearSemantics(); _innerNode = null; } } // Not using a RestorableDouble because we want to allow null values and override // [enabled]. class _RestorableScrollOffset extends RestorableValue<double?> { @override double? createDefaultValue() => null; @override void didUpdateValue(double? oldValue) { notifyListeners(); } @override double fromPrimitives(Object? data) { return data! as double; } @override Object? toPrimitives() { return value; } @override bool get enabled => value != null; }