Flutter刷新组件RefreshIndicator自定义样式demo

目录

• 前言
• 效果图
• RefreshIndicator初始样式
• RefreshIndicator样式修改（简单）
• RefreshIndicator样式修改（复杂）
• 简单的样式修改
• 复杂的样式修改

前言

RefreshIndicator是Flutter里常见的下拉刷新组件，使用是比较方便的。但由于产品兄弟对其固定的刷新样式很是不满，而且代码中已经引入了很多RefreshIndicator，直接替换其他组件的话，对代码的改动可能比较大，所以只能自己动手改一改源码，在达到产品的要求的同时尽可能减少代码的修改。

效果图

RefreshIndicator初始样式

RefreshIndicator样式修改（简单）

RefreshIndicator样式修改（复杂）

h2>源码修改

简单的样式修改

简单的样式修改，如想换成顺时针旋转的 iOS 风格活动指示器，只需替换对应样式代码即可。查看RefreshIndicator的源码，代码翻到最下面就可以看到其实是自定义了一个RefreshProgressIndicator样式，通过继承CircularProgressIndicator来实现初始样式。

所以我们只需简单的替换掉该样式即可实现简单的样式修改。

AnimatedBuilder(  animation: _positionController,  builder: (BuildContext context, Widget? child) {    return ClipOval(      child: Container(  padding: const EdgeInsets.all(10),  decoration: BoxDecoration(      color: widget.backgroundColor ?? Colors.white),  child: CupertinoActivityIndicator(      color: widget.color)),    );  },)

如此便可实现简单的样式修改。

复杂的样式修改

简单的样式修改只是换换样式，对刷新动作本身是没有任何修改的，也就是刷新操作样式本身没有变，只是换了个皮。而国内的刷新操作样式基本是上图效果3，所以如果要在RefreshIndicator上修改成效果3，除了要将原有样式Stack改为Column外，还需要自己处理手势，这里可以使用Listener来操作手势。

代码如下，修改的地方都有注释。

// 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 "dart:ui";import "package:flutter/cupertino.dart";import "package:flutter/material.dart";import "package:get/get.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.}/// 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.////// {@youtube 560 315 https://www.youtube.com/watch?v=ORApMlzwMdM}////// 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].////// {@tool dartpad}/// This example shows how [RefreshIndicator] can be triggered in different ways.////// ** See code in examples/api/lib/material/refresh_indicator/refresh_indicator.0.dart **/// {@end-tool}////// ## 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 RefreshIndicatorNeo 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 RefreshIndicatorNeo({    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,  })  : 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;  @override  RefreshIndicatorNeoState createState() => RefreshIndicatorNeoState();}/// Contains the state for a [RefreshIndicator]. This class can be used to/// programmatically show the refresh indicator, see the [show] method.class RefreshIndicatorNeoState extends State<RefreshIndicatorNeo>    with TickerProviderStateMixin<RefreshIndicatorNeo> {  late AnimationController _positionController;  late AnimationController _scaleController;  late Animation<double> _positionFactor;  late Animation<double> _scaleFactor;  late Animation<double> _value;  late Animation<Color?> _valueColor;  _RefreshIndicatorMode? _mode;  late 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.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 RefreshIndicatorNeo 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.axisDirection == AxisDirection.up &&notification.metrics.extentAfter == 0.0) ||    (notification.metrics.axisDirection == AxisDirection.down &&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:      case AxisDirection.up:indicatorAtTopNow = true;break;      case AxisDirection.left:      case AxisDirection.right:indicatorAtTopNow = true;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.axisDirection == AxisDirection.down &&notification.metrics.extentBefore > 0.0) ||    (notification.metrics.axisDirection == AxisDirection.up &&notification.metrics.extentAfter > 0.0)) {  _dismiss(_RefreshIndicatorMode.canceled);} else {  if (notification.metrics.axisDirection == AxisDirection.down) {    _dragOffset = _dragOffset! - notification.scrollDelta!;  } else if (notification.metrics.axisDirection == AxisDirection.up) {    _dragOffset = _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) {if (notification.metrics.axisDirection == AxisDirection.down) {  _dragOffset = _dragOffset! - notification.overscroll;} else if (notification.metrics.axisDirection == AxisDirection.up) {  _dragOffset = _dragOffset! + notification.overscroll;}_checkDragOffset(notification.metrics.viewportDimension,    needIntercept: true);      }    } 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;  }  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:      case AxisDirection.up:_isIndicatorAtTop = true;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, {bool needIntercept = true}) {    if (needIntercept) {      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<void> _dismiss(_RefreshIndicatorMode newMode, {Duration? time}) 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!) {      // 注释：刷新结束，关闭动画      case _RefreshIndicatorMode.done:_scaleController    .animateTo(1.0, duration: time ?? _kIndicatorScaleDuration)    .whenComplete(() {});_doneAnimation = Tween<double>(begin: getPos(pos.value), end: 0)    .animate(_scaleController);if (_doneAnimation != null) {  _doneAnimation?.addListener(() {    //赋值高度    pos(_doneAnimation?.value ?? 0);    if ((_doneAnimation?.value ?? 0) == 0) {      _doneAnimation = null;    }  });}break;      case _RefreshIndicatorMode.canceled:await _positionController.animateTo(0.0,    duration: time ?? _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<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;});// 注释:删掉这段代码，因为需要跟随手势，在手势释放的时候才执行，见下方手势控制onPointerUp// 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;  }  //点击时的Y  double _downY = 0.0;  //最后的移动Y  double _lastMoveY = 0.0;  //手势移动距离，对应下拉效果的位移  //因为需要制造弹性效果，调用getPos()模拟弹性  RxDouble pos = 0.0.obs;  //手势状态  MoveType moveType = MoveType.UP;  final double bottomImg = 10;  //手势下拉动画，主要对pos赋值  late Animation<double>? _animation;  //结束动画，主要对pos重新赋值至0  late Animation<double>? _doneAnimation;  late AnimationController _controller;  ///模拟下拉的弹性  double getPos(double pos) {    if (pos <= 0) {      return 0;    } else if (pos < 100) {      return pos * 0.7;    } else if (pos < 200) {      return 70 + ((pos - 100) * 0.5);    } else if (pos < 300) {      return 120 + ((pos - 200) * 0.3);    } else {      return 150 + ((pos - 300) * 0.1);    }  }  @override  Widget build(BuildContext context) {    assert(debugCheckHasMaterialLocalizations(context));    final Widget child = NotificationListener<ScrollNotification>(      onNotification: _handleScrollNotification,      child: widget.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;    double imgHeight = MediaQueryData.fromWindow(window).size.width / 7;    double imgAllHeight = imgHeight + bottomImg;    return Listener(onPointerDown: (PointerDownEvent event) {  //手指按下的距离  _downY = event.position.distance;  moveType = MoveType.DOWN;},onPointerMove: (PointerMoveEvent event) {  if (moveType != MoveType.MOVE || _mode == null) {    setState(() {      moveType = MoveType.MOVE;    });  }  moveType = MoveType.MOVE;  //手指移动的距离  var position = event.position.distance;  //判断距离差  var detal = position - _lastMoveY;  ///到达顶部才计算  if (_isIndicatorAtTop != null &&      _isIndicatorAtTop! &&      _mode != null) {    pos(position - _downY);    if (detal > 0) {      //================向下移动================    } else {      //================向上移动================      ///当刷新动画执行时，手指上滑就直接取消刷新动画      if (_mode == _RefreshIndicatorMode.refresh && pos.value != 0) {_dismiss(_RefreshIndicatorMode.canceled,    time: Duration(microseconds: 500));      }    }  }  _lastMoveY = position;},onPointerUp: (PointerUpEvent event) {  if (_isIndicatorAtTop != null && _isIndicatorAtTop!) {    double heightPos = pos.value;    double imgHeight = 0;    ///计算图片高度，因为最终转成pos，因为pos被转换过getPos()    //所以反转的时候需要再次计算    if (imgAllHeight < 100) {      imgHeight = imgAllHeight / 0.7;    } else if (imgAllHeight < 200) {      imgHeight = (imgAllHeight - 20) / 0.5;    } else if (imgAllHeight < 300) {      imgHeight = (imgAllHeight - 60) / 0.3;    }    //松手后的回弹效果    _controller = AnimationController(      vsync: this,      duration: Duration(milliseconds: 250),    )..forward().whenComplete(() {///动画结束后触发onRefresh()方法if (_mode == _RefreshIndicatorMode.refresh) {  final Completer<void> completer = Completer<void>();  _pendingRefreshFuture = completer.future;  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();      ///onRefresh()执行完后关闭动画      _dismiss(_RefreshIndicatorMode.done);    }  });}      });    _animation = Tween<double>(begin: heightPos, end: imgHeight).animate(_controller);    _animation?.addListener(() {      //下拉动画变化，赋值高度      if (_mode == _RefreshIndicatorMode.refresh) {pos(_animation?.value ?? 0);if (_animation?.value == imgHeight) {  _animation = null;}      }    });  }  moveType = MoveType.UP;},child: Obx(() => Column(      children: [if (_isIndicatorAtTop != null &&_isIndicatorAtTop! &&_mode != null &&moveType == MoveType.MOVE ||    pos.value != 0)  ScaleTransition(    scale: _scaleFactor,    child: AnimatedBuilder(      animation: _positionController,      builder: (BuildContext context, Widget? child) {//使用gif动画return Obx(() => Container(      height: getPos(pos.value),      alignment: Alignment.bottomCenter,      child: Container(padding: EdgeInsets.only(bottom: bottomImg),child: Image.asset(  "assets/gif_load.gif",  width: imgHeight * 2,  height: imgHeight,),      ),    ));      },    ),  ),Expanded(child: child),      ],    )));  }}enum MoveType {  DOWN,  MOVE,  UP,}

代码如上，其中还额外使用了GetX来控制手势位移距离，然后再将末尾的assets/gif_load.gif更换为各自需要的gif资源即可。

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