RefreshIndicator moves down a bit fast when the viewport is small

[takassh]

Steps to Reproduce

1. Execute flutter run on the code sample
2. Pull to refresh
3. See that RefreshIndicator moves to bottom too fast

Expected results:

https://user-images.githubusercontent.com/52235899/144551526-6f36aba0-3b77-4f7c-b9e6-3b4d86a22998.mov

Actual results:

https://user-images.githubusercontent.com/52235899/144551864-0bf33c71-7c2d-48cc-9be1-210ffa184bca.mov

Code sample

```dart import 'package:flutter/material.dart'; import 'package:flutter_pr/costom_nested_scroll%20copy.dart'; import 'package:flutter_pr/narrow_scroll.dart'; import 'package:flutter_pr/nested_scroll.dart'; import 'package:flutter_pr/scroll.dart'; void main() { runApp(const MyApp()); } class MyApp extends StatelessWidget { const MyApp({Key? key}) : super(key: key); // This widget is the root of your application. @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter Demo', theme: ThemeData( // This is the theme of your application. // // Try running your application with "flutter run". You'll see the // application has a blue toolbar. Then, without quitting the app, try // changing the primarySwatch below to Colors.green and then invoke // "hot reload" (press "r" in the console where you ran "flutter run", // or simply save your changes to "hot reload" in a Flutter IDE). // Notice that the counter didn't reset back to zero; the application // is not restarted. primarySwatch: Colors.blue, ), home: const HomePage(), ); } } class HomePage extends StatefulWidget { const HomePage({Key? key}) : super(key: key); @override State createState() => _HomePageState(); } class _HomePageState extends State { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: const Text('app bar'), ), body: RefreshIndicator( onRefresh: () { return Future.delayed(const Duration(seconds: 1)); }, child: Column( children: [ Expanded( child: ListView.builder( padding: EdgeInsets.zero, itemCount: 30, itemBuilder: (context, index) { return ListTile( key: Key('$index'), title: Center( child: Text('ListTile ${index + 1}'), ), ); }, ), ), Container(color: Colors.grey, height: 600), ], ), ), ); } } ```

This bug also causes strange movement below

https://user-images.githubusercontent.com/52235899/144552950-6f158b8c-531f-4118-98fb-f99b7d98ab73.mov

I know this bug is caused by too small ScrollMetrics.viewportDimension

[darshankawar]

@takassh Can you check this issue and see if resembles your case ?

[takassh]

@darshankawar Thank you for reply. I checked it.

71819 seems to point out the "padding" while mine points out the "speed".

If there is enough space for the indicator to move down and for the user to drag down, the indicator should move slowly, as shown in the expected result above. The actual result shows the indicator is following the users drag too closely.

[darshankawar]

Thanks for the update. I see the same behavior on latest master and stable.

stable, master flutter doctor -v

``` [✓] Flutter (Channel stable, 2.5.3, on Mac OS X 10.15.4 19E2269 darwin-x64, locale en-GB) • Flutter version 2.5.3 at /Users/dhs/documents/fluttersdk/flutter • Upstream repository https://github.com/flutter/flutter.git • Framework revision 18116933e7 (2 days ago), 2021-10-15 10:46:35 -0700 • Engine revision d3ea636dc5 • Dart version 2.14.4 [✓] Android toolchain - develop for Android devices (Android SDK version 30) • Android SDK at /Users/dhs/Library/Android/sdk • Platform android-30, build-tools 30.0.3 • ANDROID_HOME = /Users/dhs/Library/Android/sdk • Java binary at: /Users/dhs/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/202.7486908/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495) • All Android licenses accepted. [✓] Xcode - develop for iOS and macOS • Xcode at /Applications/Xcode.app/Contents/Developer • Xcode 12.3, Build version 12C33 • CocoaPods version 1.10.1 [✓] Chrome - develop for the web • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome [✓] Android Studio (version 4.1) • Android Studio at /Users/dhs/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/202.7486908/Android Studio.app/Contents • Flutter plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/9212-flutter • Dart plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/6351-dart • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495) [✓] VS Code (version 1.57.1) • VS Code at /Applications/Visual Studio Code.app/Contents • Flutter extension version 3.21.0 [✓] Connected device (4 available) • Darshan's iphone (mobile) • 21150b119064aecc249dfcfe05e259197461ce23 • ios • iOS 14.4.1 18D61 • iPhone 12 Pro Max (mobile) • A5473606-0213-4FD8-BA16-553433949729 • ios • com.apple.CoreSimulator.SimRuntime.iOS-14-3 (simulator) • macOS (desktop) • macos • darwin-x64 • Mac OS X 10.15.4 19E2269 darwin-x64 • Chrome (web) • chrome • web-javascript • Google Chrome 93.0.4577.82 • No issues found! [✓] Flutter (Channel master, 2.6.0-12.0.pre.924, on Mac OS X 10.15.4 19E2269 darwin-x64, locale en-GB) • Flutter version 2.6.0-12.0.pre.924 at /Users/dhs/documents/fluttersdk/flutter • Upstream repository https://github.com/flutter/flutter.git • Framework revision eb221c4544 (12 hours ago), 2021-12-05 11:49:04 -0500 • Engine revision 68d320d449 • Dart version 2.16.0 (build 2.16.0-80.0.dev) • DevTools version 2.9.1 [✓] Android toolchain - develop for Android devices (Android SDK version 30) • Android SDK at /Users/dhs/Library/Android/sdk • Platform android-30, build-tools 30.0.3 • ANDROID_HOME = /Users/dhs/Library/Android/sdk • Java binary at: /Users/dhs/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/202.7486908/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495) • All Android licenses accepted. [✓] Xcode - develop for iOS and macOS • Xcode at /Applications/Xcode.app/Contents/Developer • Xcode 12.5.1, Build version 12E507 • CocoaPods version 1.10.1 [✓] Chrome - develop for the web • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome [✓] Android Studio (version 4.1) • Android Studio at /Users/dhs/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/202.7486908/Android Studio.app/Contents • Flutter plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/9212-flutter • Dart plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/6351-dart • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495) [✓] VS Code (version 1.57.1) • VS Code at /Applications/Visual Studio Code.app/Contents • Flutter extension version 3.21.0 [[✓] Connected device (4 available) • Darshan's iphone (mobile) • 21150b119064aecc249dfcfe05e259197461ce23 • ios • iOS 14.4.1 18D61 • iPhone 12 Pro Max (mobile) • A5473606-0213-4FD8-BA16-553433949729 • ios • com.apple.CoreSimulator.SimRuntime.iOS-14-3 (simulator) • macOS (desktop) • macos • darwin-x64 • Mac OS X 10.15.4 19E2269 darwin-x64 • Chrome (web) • chrome • web-javascript • Google Chrome 93.0.4577.82 • No issues found! ```

complete code sample

``` import 'package:flutter/material.dart'; void main() { runApp(const MyApp()); } class MyApp extends StatelessWidget { const MyApp({Key? key}) : super(key: key); // This widget is the root of your application. @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter Demo', theme: ThemeData( // This is the theme of your application. // // Try running your application with "flutter run". You'll see the // application has a blue toolbar. Then, without quitting the app, try // changing the primarySwatch below to Colors.green and then invoke // "hot reload" (press "r" in the console where you ran "flutter run", // or simply save your changes to "hot reload" in a Flutter IDE). // Notice that the counter didn't reset back to zero; the application // is not restarted. primarySwatch: Colors.blue, ), home: const HomePage(), ); } } class HomePage extends StatefulWidget { const HomePage({Key? key}) : super(key: key); @override State createState() => _HomePageState(); } class _HomePageState extends State { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: const Text('app bar'), ), body: RefreshIndicator( onRefresh: () { return Future.delayed(const Duration(seconds: 1)); }, child: Column( children: [ Expanded( child: ListView.builder( padding: EdgeInsets.zero, itemCount: 30, itemBuilder: (context, index) { return ListTile( key: Key('$index'), title: Center( child: Text('ListTile ${index + 1}'), ), ); }, ), ), Container(color: Colors.grey, height: 600), ], ), ), ); } } ```

[takassh]

@darshankawar Thank you for checking.

For now, I could fix this bug like the code below (sorry for long). Could I create PR? (I have never create PR for Flutter before)

new material/refresh_indicator.dart

```dart // 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 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. } /// Used to configure how [RefreshIndicator] can be triggered. enum RefreshIndicatorTriggerMode { /// The indicator can be triggered regardless of the scroll position /// of the [Scrollable] when the drag starts. anywhere, /// The indicator can only be triggered if the [Scrollable] is at the edge /// when the drag starts. onEdge, } /// 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. /// /// The trigger mode is configured by [RefreshIndicator.triggerMode]. /// /// ## 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: /// /// * /// * [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, this.edgeOffset = 0.0, required this.onRefresh, this.color, this.backgroundColor, this.notificationPredicate = defaultScrollNotificationPredicate, this.semanticsLabel, this.semanticsValue, this.strokeWidth = RefreshProgressIndicator.defaultStrokeWidth, this.triggerMode = RefreshIndicatorTriggerMode.onEdge, this.isSmallDimention = false, }) : assert(child != null), assert(onRefresh != null), assert(notificationPredicate != null), assert(strokeWidth != null), assert(triggerMode != 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 [edgeOffset] where /// the refresh indicator will settle. During the drag that exposes the refresh /// indicator, its actual displacement may significantly exceed this value. /// /// In most cases, [displacement] distance starts counting from the parent's /// edges. However, if [edgeOffset] is larger than zero then the [displacement] /// value is calculated from that offset instead of the parent's edge. final double displacement; /// The offset where [RefreshProgressIndicator] starts to appear on drag start. /// /// Depending whether the indicator is showing on the top or bottom, the value /// of this variable controls how far from the parent's edge the progress /// indicator starts to appear. This may come in handy when, for example, the /// UI contains a top [Widget] which covers the parent's edge where the progress /// indicator would otherwise appear. /// /// By default, the edge offset is set to 0. /// /// See also: /// /// * [displacement], can be used to change the distance from the edge that /// the indicator settles. final double edgeOffset; /// 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 /// [ColorScheme.primary] 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.progress_indicator.ProgressIndicator.semanticsLabel} /// /// This will be defaulted to [MaterialLocalizations.refreshIndicatorSemanticLabel] /// if it is null. final String? semanticsLabel; /// {@macro flutter.progress_indicator.ProgressIndicator.semanticsValue} final String? semanticsValue; /// Defines `strokeWidth` for `RefreshIndicator`. /// /// By default, the value of `strokeWidth` is 2.0 pixels. final double strokeWidth; /// Defines how this [RefreshIndicator] can be triggered when users overscroll. /// /// The [RefreshIndicator] can be pulled out in two cases, /// 1, Keep dragging if the scrollable widget at the edge with zero scroll position /// when the drag starts. /// 2, Keep dragging after overscroll occurs if the scrollable widget has /// a non-zero scroll position when the drag starts. /// /// If this is [RefreshIndicatorTriggerMode.anywhere], both of the cases above can be triggered. /// /// If this is [RefreshIndicatorTriggerMode.onEdge], only case 1 can be triggered. /// /// Defaults to [RefreshIndicatorTriggerMode.onEdge]. final RefreshIndicatorTriggerMode triggerMode; final bool isSmallDimention; @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 with TickerProviderStateMixin { late AnimationController _positionController; late AnimationController _scaleController; late Animation _positionFactor; late Animation _scaleFactor; late Animation _value; late Animation _valueColor; _RefreshIndicatorMode? _mode; late Future _pendingRefreshFuture; bool? _isIndicatorAtTop; double? _dragOffset; static final Animatable _threeQuarterTween = Tween(begin: 0.0, end: 0.75); static final Animatable _kDragSizeFactorLimitTween = Tween(begin: 0.0, end: _kDragSizeFactorLimit); static final Animatable _oneToZeroTween = Tween(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.colorScheme.primary).withOpacity(0.0), end: (widget.color ?? theme.colorScheme.primary).withOpacity(1.0), ).chain(CurveTween( curve: const Interval(0.0, 1.0 / _kDragSizeFactorLimit), )), ); super.didChangeDependencies(); } @override void didUpdateWidget(covariant RefreshIndicator oldWidget) { super.didUpdateWidget(oldWidget); if (oldWidget.color != widget.color) { final ThemeData theme = Theme.of(context); _valueColor = _positionController.drive( ColorTween( begin: (widget.color ?? theme.colorScheme.primary).withOpacity(0.0), end: (widget.color ?? theme.colorScheme.primary).withOpacity(1.0), ).chain(CurveTween( curve: const Interval(0.0, 1.0 / _kDragSizeFactorLimit), )), ); } } @override void dispose() { _positionController.dispose(); _scaleController.dispose(); super.dispose(); } bool _shouldStart(ScrollNotification notification) { // If the notification.dragDetails is null, this scroll is not triggered by // user dragging. It may be a result of ScrollController.jumpTo or ballistic scroll. // In this case, we don't want to trigger the refresh indicator. return ((notification is ScrollStartNotification && notification.dragDetails != null) || (notification is ScrollUpdateNotification && notification.dragDetails != null && widget.triggerMode == RefreshIndicatorTriggerMode.anywhere)) && notification.metrics.extentBefore == 0.0 && _mode == null && _start(notification.metrics.axisDirection); } bool _handleScrollNotification(ScrollNotification notification) { if (!widget.notificationPredicate(notification)) return false; if (_shouldStart(notification)) { 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 { if (widget.isSmallDimention) { _dragOffset = _dragOffset! - notification.scrollDelta!; _checkDragOffset(notification.metrics.viewportDimension); } else { final delta = _applyPhysicsToUserOffset(notification) ?? 0; _dragOffset = _dragOffset! + delta; _checkDragOffset((context.findRenderObject()! as RenderBox).size.height); } } } 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 = _dragOffset! - notification.overscroll; _checkDragOffset(notification.metrics.viewportDimension); } } else if (notification is ScrollEndNotification) { switch (_mode) { case _RefreshIndicatorMode.armed: _show(); break; case _RefreshIndicatorMode.drag: _dismiss(_RefreshIndicatorMode.canceled); break; case _RefreshIndicatorMode.canceled: case _RefreshIndicatorMode.done: case _RefreshIndicatorMode.refresh: case _RefreshIndicatorMode.snap: case null: // do nothing break; } } return false; } double? _applyPhysicsToUserOffset(ScrollUpdateNotification notification) { final position = notification.metrics; double offset = notification.dragDetails?.primaryDelta ?? double.minPositive; assert(offset != 0.0); assert(position.minScrollExtent <= position.maxScrollExtent); if (!position.outOfRange) return offset; final double overscrollPastStart = math.max(position.minScrollExtent - position.pixels, 0.0); final double overscrollPastEnd = math.max(position.pixels - position.maxScrollExtent, 0.0); final double overscrollPast = math.max(overscrollPastStart, overscrollPastEnd); final bool easing = (overscrollPastStart > 0.0 && offset < 0.0) || (overscrollPastEnd > 0.0 && offset > 0.0); final double friction = easing // Apply less resistance when easing the overscroll vs tensioning. ? _frictionFactor((overscrollPast - offset.abs()) / (context.findRenderObject()! as RenderBox).size.height) : _frictionFactor(overscrollPast / (context.findRenderObject()! as RenderBox).size.height); final double direction = offset.sign; return direction * _applyFriction(overscrollPast, offset.abs(), friction); } double _frictionFactor(double overscrollFraction) => 0.52 * math.pow(1 - overscrollFraction, 2); double _applyFriction(double extentOutside, double absDelta, double gamma) { assert(absDelta > 0); double total = 0.0; if (extentOutside > 0) { final double deltaToLimit = extentOutside / gamma; if (absDelta < deltaToLimit) return absDelta * gamma; total += extentOutside; absDelta -= deltaToLimit; } return total + absDelta; } 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); // this triggers various rebuilds if (_mode == _RefreshIndicatorMode.drag && _valueColor.value!.alpha == 0xFF) _mode = _RefreshIndicatorMode.armed; } // Stop showing the refresh indicator. Future _dismiss(_RefreshIndicatorMode newMode) async { await Future.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; case _RefreshIndicatorMode.armed: case _RefreshIndicatorMode.drag: case _RefreshIndicatorMode.refresh: case _RefreshIndicatorMode.snap: 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 completer = Completer(); _pendingRefreshFuture = completer.future; _mode = _RefreshIndicatorMode.snap; _positionController .animateTo(1.0 / _kDragSizeFactorLimit, duration: _kIndicatorSnapDuration) .then((void value) { if (mounted && _mode == _RefreshIndicatorMode.snap) { assert(widget.onRefresh != null); setState(() { // Show the indeterminate progress indicator. _mode = _RefreshIndicatorMode.refresh; }); final Future 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] /// 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 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( onNotification: _handleScrollNotification, child: NotificationListener( 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: [ child, if (_mode != null) Positioned( top: _isIndicatorAtTop! ? widget.edgeOffset : null, bottom: !_isIndicatorAtTop! ? widget.edgeOffset : 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, ); }, ), ), ), ), ), ], ); } } ```