// 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/widgets.dart'; import 'debug.dart'; import 'material_localizations.dart'; import 'progress_indicator.dart'; import 'theme.dart'; // The over-scroll distance that moves the indicator to its maximum // displacement, as a percentage of the scrollable's container extent. const double _kDragContainerExtentPercentage = 0.25; // How much the scroll's drag gesture can overshoot the RefreshIndicator's // displacement; max displacement = _kDragSizeFactorLimit * displacement. const double _kDragSizeFactorLimit = 1.5; // When the scroll ends, the duration of the refresh indicator's animation // to the RefreshIndicator's displacement. const Duration _kIndicatorSnapDuration = Duration(milliseconds: 150); // The duration of the ScaleTransition that starts when the refresh action // has completed. const Duration _kIndicatorScaleDuration = Duration(milliseconds: 200); /// The signature for a function that's called when the user has dragged a /// [RefreshIndicator] far enough to demonstrate that they want the app to /// refresh. The returned [Future] must complete when the refresh operation is /// finished. /// /// Used by [RefreshIndicator.onRefresh]. typedef RefreshCallback = Future<void> Function(); // The state machine moves through these modes only when the scrollable // identified by scrollableKey has been scrolled to its min or max limit. enum _RefreshIndicatorMode { drag, // Pointer is down. armed, // Dragged far enough that an up event will run the onRefresh callback. snap, // Animating to the indicator's final "displacement". refresh, // Running the refresh callback. done, // Animating the indicator's fade-out after refreshing. canceled, // Animating the indicator's fade-out after not arming. } /// A widget that supports the Material "swipe to refresh" idiom. /// /// When the child's [Scrollable] descendant overscrolls, an animated circular /// progress indicator is faded into view. When the scroll ends, if the /// indicator has been dragged far enough for it to become completely opaque, /// the [onRefresh] callback is called. The callback is expected to update the /// scrollable's contents and then complete the [Future] it returns. The refresh /// indicator disappears after the callback's [Future] has completed. /// /// ## Troubleshooting /// /// ### Refresh indicator does not show up /// /// The [RefreshIndicator] will appear if its scrollable descendant can be /// overscrolled, i.e. if the scrollable's content is bigger than its viewport. /// To ensure that the [RefreshIndicator] will always appear, even if the /// scrollable's content fits within its viewport, set the scrollable's /// [Scrollable.physics] property to [AlwaysScrollableScrollPhysics]: /// /// ```dart /// ListView( /// physics: const AlwaysScrollableScrollPhysics(), /// children: ... /// ) /// ``` /// /// A [RefreshIndicator] can only be used with a vertical scroll view. /// /// See also: /// /// * <https://material.io/design/platform-guidance/android-swipe-to-refresh.html> /// * [RefreshIndicatorState], can be used to programmatically show the refresh indicator. /// * [RefreshProgressIndicator], widget used by [RefreshIndicator] to show /// the inner circular progress spinner during refreshes. /// * [CupertinoSliverRefreshControl], an iOS equivalent of the pull-to-refresh pattern. /// Must be used as a sliver inside a [CustomScrollView] instead of wrapping /// around a [ScrollView] because it's a part of the scrollable instead of /// being overlaid on top of it. class RefreshIndicator extends StatefulWidget { /// Creates a refresh indicator. /// /// The [onRefresh], [child], and [notificationPredicate] arguments must be /// non-null. The default /// [displacement] is 40.0 logical pixels. /// /// The [semanticsLabel] is used to specify an accessibility label for this widget. /// If it is null, it will be defaulted to [MaterialLocalizations.refreshIndicatorSemanticLabel]. /// An empty string may be passed to avoid having anything read by screen reading software. /// The [semanticsValue] may be used to specify progress on the widget. const RefreshIndicator({ Key key, @required this.child, this.displacement = 40.0, @required this.onRefresh, this.color, this.backgroundColor, this.notificationPredicate = defaultScrollNotificationPredicate, this.semanticsLabel, this.semanticsValue, this.strokeWidth = 2.0 }) : assert(child != null), assert(onRefresh != null), assert(notificationPredicate != null), assert(strokeWidth != null), super(key: key); /// The widget below this widget in the tree. /// /// The refresh indicator will be stacked on top of this child. The indicator /// will appear when child's Scrollable descendant is over-scrolled. /// /// Typically a [ListView] or [CustomScrollView]. final Widget child; /// The distance from the child's top or bottom edge to where the refresh /// indicator will settle. During the drag that exposes the refresh indicator, /// its actual displacement may significantly exceed this value. final double displacement; /// A function that's called when the user has dragged the refresh indicator /// far enough to demonstrate that they want the app to refresh. The returned /// [Future] must complete when the refresh operation is finished. final RefreshCallback onRefresh; /// The progress indicator's foreground color. The current theme's /// [ThemeData.accentColor] by default. final Color color; /// The progress indicator's background color. The current theme's /// [ThemeData.canvasColor] by default. final Color backgroundColor; /// A check that specifies whether a [ScrollNotification] should be /// handled by this widget. /// /// By default, checks whether `notification.depth == 0`. Set it to something /// else for more complicated layouts. final ScrollNotificationPredicate notificationPredicate; /// {@macro flutter.material.progressIndicator.semanticsLabel} /// /// This will be defaulted to [MaterialLocalizations.refreshIndicatorSemanticLabel] /// if it is null. final String semanticsLabel; /// {@macro flutter.material.progressIndicator.semanticsValue} final String semanticsValue; /// Defines `strokeWidth` for `RefreshIndicator`. /// /// By default, the value of `strokeWidth` is 2.0 pixels. final double strokeWidth; @override RefreshIndicatorState createState() => RefreshIndicatorState(); } /// Contains the state for a [RefreshIndicator]. This class can be used to /// programmatically show the refresh indicator, see the [show] method. class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderStateMixin<RefreshIndicator> { AnimationController _positionController; AnimationController _scaleController; Animation<double> _positionFactor; Animation<double> _scaleFactor; Animation<double> _value; Animation<Color> _valueColor; _RefreshIndicatorMode _mode; Future<void> _pendingRefreshFuture; bool _isIndicatorAtTop; double _dragOffset; static final Animatable<double> _threeQuarterTween = Tween<double>(begin: 0.0, end: 0.75); static final Animatable<double> _kDragSizeFactorLimitTween = Tween<double>(begin: 0.0, end: _kDragSizeFactorLimit); static final Animatable<double> _oneToZeroTween = Tween<double>(begin: 1.0, end: 0.0); @override void initState() { super.initState(); _positionController = AnimationController(vsync: this); _positionFactor = _positionController.drive(_kDragSizeFactorLimitTween); _value = _positionController.drive(_threeQuarterTween); // The "value" of the circular progress indicator during a drag. _scaleController = AnimationController(vsync: this); _scaleFactor = _scaleController.drive(_oneToZeroTween); } @override void didChangeDependencies() { final ThemeData theme = Theme.of(context); _valueColor = _positionController.drive( ColorTween( begin: (widget.color ?? theme.accentColor).withOpacity(0.0), end: (widget.color ?? theme.accentColor).withOpacity(1.0), ).chain(CurveTween( curve: const Interval(0.0, 1.0 / _kDragSizeFactorLimit) )), ); super.didChangeDependencies(); } @override void dispose() { _positionController.dispose(); _scaleController.dispose(); super.dispose(); } bool _handleScrollNotification(ScrollNotification notification) { if (!widget.notificationPredicate(notification)) return false; if (notification is ScrollStartNotification && notification.metrics.extentBefore == 0.0 && _mode == null && _start(notification.metrics.axisDirection)) { setState(() { _mode = _RefreshIndicatorMode.drag; }); return false; } bool indicatorAtTopNow; switch (notification.metrics.axisDirection) { case AxisDirection.down: indicatorAtTopNow = true; break; case AxisDirection.up: indicatorAtTopNow = false; break; case AxisDirection.left: case AxisDirection.right: indicatorAtTopNow = null; break; } if (indicatorAtTopNow != _isIndicatorAtTop) { if (_mode == _RefreshIndicatorMode.drag || _mode == _RefreshIndicatorMode.armed) _dismiss(_RefreshIndicatorMode.canceled); } else if (notification is ScrollUpdateNotification) { if (_mode == _RefreshIndicatorMode.drag || _mode == _RefreshIndicatorMode.armed) { if (notification.metrics.extentBefore > 0.0) { _dismiss(_RefreshIndicatorMode.canceled); } else { _dragOffset -= notification.scrollDelta; _checkDragOffset(notification.metrics.viewportDimension); } } if (_mode == _RefreshIndicatorMode.armed && notification.dragDetails == null) { // On iOS start the refresh when the Scrollable bounces back from the // overscroll (ScrollNotification indicating this don't have dragDetails // because the scroll activity is not directly triggered by a drag). _show(); } } else if (notification is OverscrollNotification) { if (_mode == _RefreshIndicatorMode.drag || _mode == _RefreshIndicatorMode.armed) { _dragOffset -= notification.overscroll / 2.0; _checkDragOffset(notification.metrics.viewportDimension); } } else if (notification is ScrollEndNotification) { switch (_mode) { case _RefreshIndicatorMode.armed: _show(); break; case _RefreshIndicatorMode.drag: _dismiss(_RefreshIndicatorMode.canceled); break; default: // do nothing break; } } return false; } bool _handleGlowNotification(OverscrollIndicatorNotification notification) { if (notification.depth != 0 || !notification.leading) return false; if (_mode == _RefreshIndicatorMode.drag) { notification.disallowGlow(); return true; } return false; } bool _start(AxisDirection direction) { assert(_mode == null); assert(_isIndicatorAtTop == null); assert(_dragOffset == null); switch (direction) { case AxisDirection.down: _isIndicatorAtTop = true; break; case AxisDirection.up: _isIndicatorAtTop = false; break; case AxisDirection.left: case AxisDirection.right: _isIndicatorAtTop = null; // we do not support horizontal scroll views. return false; } _dragOffset = 0.0; _scaleController.value = 0.0; _positionController.value = 0.0; return true; } void _checkDragOffset(double containerExtent) { assert(_mode == _RefreshIndicatorMode.drag || _mode == _RefreshIndicatorMode.armed); double newValue = _dragOffset / (containerExtent * _kDragContainerExtentPercentage); if (_mode == _RefreshIndicatorMode.armed) newValue = math.max(newValue, 1.0 / _kDragSizeFactorLimit); _positionController.value = newValue.clamp(0.0, 1.0) as double; // this triggers various rebuilds if (_mode == _RefreshIndicatorMode.drag && _valueColor.value.alpha == 0xFF) _mode = _RefreshIndicatorMode.armed; } // Stop showing the refresh indicator. Future<void> _dismiss(_RefreshIndicatorMode newMode) async { await Future<void>.value(); // This can only be called from _show() when refreshing and // _handleScrollNotification in response to a ScrollEndNotification or // direction change. assert(newMode == _RefreshIndicatorMode.canceled || newMode == _RefreshIndicatorMode.done); setState(() { _mode = newMode; }); switch (_mode) { case _RefreshIndicatorMode.done: await _scaleController.animateTo(1.0, duration: _kIndicatorScaleDuration); break; case _RefreshIndicatorMode.canceled: await _positionController.animateTo(0.0, duration: _kIndicatorScaleDuration); break; default: assert(false); } if (mounted && _mode == newMode) { _dragOffset = null; _isIndicatorAtTop = null; setState(() { _mode = null; }); } } void _show() { assert(_mode != _RefreshIndicatorMode.refresh); assert(_mode != _RefreshIndicatorMode.snap); final Completer<void> completer = Completer<void>(); _pendingRefreshFuture = completer.future; _mode = _RefreshIndicatorMode.snap; _positionController .animateTo(1.0 / _kDragSizeFactorLimit, duration: _kIndicatorSnapDuration) .then<void>((void value) { if (mounted && _mode == _RefreshIndicatorMode.snap) { assert(widget.onRefresh != null); setState(() { // Show the indeterminate progress indicator. _mode = _RefreshIndicatorMode.refresh; }); final Future<void> refreshResult = widget.onRefresh(); assert(() { if (refreshResult == null) FlutterError.reportError(FlutterErrorDetails( exception: FlutterError( 'The onRefresh callback returned null.\n' 'The RefreshIndicator onRefresh callback must return a Future.' ), context: ErrorDescription('when calling onRefresh'), library: 'material library', )); return true; }()); if (refreshResult == null) return; refreshResult.whenComplete(() { if (mounted && _mode == _RefreshIndicatorMode.refresh) { completer.complete(); _dismiss(_RefreshIndicatorMode.done); } }); } }); } /// Show the refresh indicator and run the refresh callback as if it had /// been started interactively. If this method is called while the refresh /// callback is running, it quietly does nothing. /// /// Creating the [RefreshIndicator] with a [GlobalKey<RefreshIndicatorState>] /// makes it possible to refer to the [RefreshIndicatorState]. /// /// The future returned from this method completes when the /// [RefreshIndicator.onRefresh] callback's future completes. /// /// If you await the future returned by this function from a [State], you /// should check that the state is still [mounted] before calling [setState]. /// /// When initiated in this manner, the refresh indicator is independent of any /// actual scroll view. It defaults to showing the indicator at the top. To /// show it at the bottom, set `atTop` to false. Future<void> show({ bool atTop = true }) { if (_mode != _RefreshIndicatorMode.refresh && _mode != _RefreshIndicatorMode.snap) { if (_mode == null) _start(atTop ? AxisDirection.down : AxisDirection.up); _show(); } return _pendingRefreshFuture; } @override Widget build(BuildContext context) { assert(debugCheckHasMaterialLocalizations(context)); final Widget child = NotificationListener<ScrollNotification>( onNotification: _handleScrollNotification, child: NotificationListener<OverscrollIndicatorNotification>( onNotification: _handleGlowNotification, child: widget.child, ), ); assert(() { if (_mode == null) { assert(_dragOffset == null); assert(_isIndicatorAtTop == null); } else { assert(_dragOffset != null); assert(_isIndicatorAtTop != null); } return true; }()); final bool showIndeterminateIndicator = _mode == _RefreshIndicatorMode.refresh || _mode == _RefreshIndicatorMode.done; return Stack( children: <Widget>[ child, if (_mode != null) Positioned( top: _isIndicatorAtTop ? 0.0 : null, bottom: !_isIndicatorAtTop ? 0.0 : null, left: 0.0, right: 0.0, child: SizeTransition( axisAlignment: _isIndicatorAtTop ? 1.0 : -1.0, sizeFactor: _positionFactor, // this is what brings it down child: Container( padding: _isIndicatorAtTop ? EdgeInsets.only(top: widget.displacement) : EdgeInsets.only(bottom: widget.displacement), alignment: _isIndicatorAtTop ? Alignment.topCenter : Alignment.bottomCenter, child: ScaleTransition( scale: _scaleFactor, child: AnimatedBuilder( animation: _positionController, builder: (BuildContext context, Widget child) { return RefreshProgressIndicator( semanticsLabel: widget.semanticsLabel ?? MaterialLocalizations.of(context).refreshIndicatorSemanticLabel, semanticsValue: widget.semanticsValue, value: showIndeterminateIndicator ? null : _value.value, valueColor: _valueColor, backgroundColor: widget.backgroundColor, strokeWidth: widget.strokeWidth, ); }, ), ), ), ), ), ], ); } }