// 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. // @dart = 2.8 import 'dart:async'; import 'package:flutter/cupertino.dart'; import 'package:flutter/widgets.dart'; import 'theme.dart'; const double _kScrollbarThickness = 6.0; const Duration _kScrollbarFadeDuration = Duration(milliseconds: 300); const Duration _kScrollbarTimeToFade = Duration(milliseconds: 600); /// A material design scrollbar. /// /// A scrollbar indicates which portion of a [Scrollable] widget is actually /// visible. /// /// Dynamically changes to an iOS style scrollbar that looks like /// [CupertinoScrollbar] on the iOS platform. /// /// To add a scrollbar to a [ScrollView], simply wrap the scroll view widget in /// a [Scrollbar] widget. /// /// See also: /// /// * [ListView], which display a linear, scrollable list of children. /// * [GridView], which display a 2 dimensional, scrollable array of children. class Scrollbar extends StatefulWidget { /// Creates a material design scrollbar that wraps the given [child]. /// /// The [child] should be a source of [ScrollNotification] notifications, /// typically a [Scrollable] widget. const Scrollbar({ Key key, @required this.child, this.controller, this.isAlwaysShown = false, }) : assert(!isAlwaysShown || controller != null, 'When isAlwaysShown is true, must pass a controller that is attached to a scroll view'), super(key: key); /// The widget below this widget in the tree. /// /// The scrollbar will be stacked on top of this child. This child (and its /// subtree) should include a source of [ScrollNotification] notifications. /// /// Typically a [ListView] or [CustomScrollView]. final Widget child; /// {@macro flutter.cupertino.cupertinoScrollbar.controller} final ScrollController controller; /// {@macro flutter.cupertino.cupertinoScrollbar.isAlwaysShown} final bool isAlwaysShown; @override _ScrollbarState createState() => _ScrollbarState(); } class _ScrollbarState extends State<Scrollbar> with TickerProviderStateMixin { ScrollbarPainter _materialPainter; TextDirection _textDirection; Color _themeColor; bool _useCupertinoScrollbar; AnimationController _fadeoutAnimationController; Animation<double> _fadeoutOpacityAnimation; Timer _fadeoutTimer; @override void initState() { super.initState(); _fadeoutAnimationController = AnimationController( vsync: this, duration: _kScrollbarFadeDuration, ); _fadeoutOpacityAnimation = CurvedAnimation( parent: _fadeoutAnimationController, curve: Curves.fastOutSlowIn, ); } @override void didChangeDependencies() { super.didChangeDependencies(); assert((() { _useCupertinoScrollbar = null; return true; })()); final ThemeData theme = Theme.of(context); switch (theme.platform) { case TargetPlatform.iOS: case TargetPlatform.macOS: // On iOS, stop all local animations. CupertinoScrollbar has its own // animations. _fadeoutTimer?.cancel(); _fadeoutTimer = null; _fadeoutAnimationController.reset(); _useCupertinoScrollbar = true; break; case TargetPlatform.android: case TargetPlatform.fuchsia: case TargetPlatform.linux: case TargetPlatform.windows: _themeColor = theme.highlightColor.withOpacity(1.0); _textDirection = Directionality.of(context); _materialPainter = _buildMaterialScrollbarPainter(); _useCupertinoScrollbar = false; _triggerScrollbar(); break; } assert(_useCupertinoScrollbar != null); } @override void didUpdateWidget(Scrollbar oldWidget) { super.didUpdateWidget(oldWidget); if (widget.isAlwaysShown != oldWidget.isAlwaysShown) { if (widget.isAlwaysShown == false) { _fadeoutAnimationController.reverse(); } else { _triggerScrollbar(); _fadeoutAnimationController.animateTo(1.0); } } } // Wait one frame and cause an empty scroll event. This allows the thumb to // show immediately when isAlwaysShown is true. A scroll event is required in // order to paint the thumb. void _triggerScrollbar() { WidgetsBinding.instance.addPostFrameCallback((Duration duration) { if (widget.isAlwaysShown) { _fadeoutTimer?.cancel(); widget.controller.position.didUpdateScrollPositionBy(0); } }); } ScrollbarPainter _buildMaterialScrollbarPainter() { return ScrollbarPainter( color: _themeColor, textDirection: _textDirection, thickness: _kScrollbarThickness, fadeoutOpacityAnimation: _fadeoutOpacityAnimation, padding: MediaQuery.of(context).padding, ); } bool _handleScrollNotification(ScrollNotification notification) { final ScrollMetrics metrics = notification.metrics; if (metrics.maxScrollExtent <= metrics.minScrollExtent) { return false; } // iOS sub-delegates to the CupertinoScrollbar instead and doesn't handle // scroll notifications here. if (!_useCupertinoScrollbar && (notification is ScrollUpdateNotification || notification is OverscrollNotification)) { if (_fadeoutAnimationController.status != AnimationStatus.forward) { _fadeoutAnimationController.forward(); } _materialPainter.update( notification.metrics, notification.metrics.axisDirection, ); if (!widget.isAlwaysShown) { _fadeoutTimer?.cancel(); _fadeoutTimer = Timer(_kScrollbarTimeToFade, () { _fadeoutAnimationController.reverse(); _fadeoutTimer = null; }); } } return false; } @override void dispose() { _fadeoutAnimationController.dispose(); _fadeoutTimer?.cancel(); _materialPainter?.dispose(); super.dispose(); } @override Widget build(BuildContext context) { if (_useCupertinoScrollbar) { return CupertinoScrollbar( child: widget.child, isAlwaysShown: widget.isAlwaysShown, controller: widget.controller, ); } return NotificationListener<ScrollNotification>( onNotification: _handleScrollNotification, child: RepaintBoundary( child: CustomPaint( foregroundPainter: _materialPainter, child: RepaintBoundary( child: widget.child, ), ), ), ); } }