flutter页面滚动联动实现

import 'dart:math' as math; import 'package:flutter/gestures.dart'; import 'package:flutter/physics.dart'; import 'package:flutter/rendering.dart'; import 'package:flutter/widgets.dart'; import 'customScrollCoordinator.dart'; /// 滑动位置信息 class CustomScrollPosition extends ScrollPosition implements ScrollActivityDelegate { CustomScrollPosition({ @required ScrollPhysics physics, @required ScrollContext context, double initialPixels = 0.0, bool keepScrollOffset = true, ScrollPosition oldPosition, String debugLabel, @required this.coordinator, }) : super( physics: physics, context: context, keepScrollOffset: keepScrollOffset, oldPosition: oldPosition, debugLabel: debugLabel, ) { // 如果oldPosition不为null，则父级将首先调用Absorb()，它可以设置_pixels和_activity. if (pixels == null && initialPixels != null) { correctPixels(initialPixels); } if (activity == null) { goIdle(); } assert(activity != null); } final CustomScrollCoordinator coordinator; // 协调器 ScrollDragController _currentDrag; double _heldPreviousVelocity = 0.0; @override AxisDirection get axisDirection => context.axisDirection; @override double setPixels(double newPixels) { assert(activity.isScrolling); return super.setPixels(newPixels); } @override void absorb(ScrollPosition other) { super.absorb(other); if (other is! CustomScrollPosition) { goIdle(); return; } activity.updateDelegate(this); final CustomScrollPosition typedOther = other as CustomScrollPosition; _userScrollDirection = typedOther._userScrollDirection; assert(_currentDrag == null); if (typedOther._currentDrag != null) { _currentDrag = typedOther._currentDrag; _currentDrag.updateDelegate(this); typedOther._currentDrag = null; } } @override void applyNewDimensions() { super.applyNewDimensions(); context.setCanDrag(physics.shouldAcceptUserOffset(this)); } /// 返回未使用的增量。 /// /// 正增量表示下降（在上方显示内容），负增量向上（在下方显示内容）。 double applyClampedDragUpdate(double delta) { assert(delta != 0.0); // 如果我们要朝向 maxScrollExtent（负滚动偏移），那么我们在 minScrollExtent 方向上 // 可以达到的最大距离是负无穷大。例如，如果我们已经过度滚动，则滚动以减少过度滚动不应 // 禁止过度滚动。如果我们要朝 minScrollExtent（正滚动偏移量）方向移动，那么我们在 // minScrollExtent 方向上可以达到的最大距离是我们现在所处的位置。 // 换句话说，我们不能通过 applyClampedDragUpdate 进入过滚动状态。 // 尽管如此，可能通过多种方式进入了过度滚动的情况。一种是物理是否允许通过 // applyFullDragUpdate（请参见下文）。 // 可能会发生过度滚动的情况，例如，使用滚动控制器人工设置了滚动位置。 final double min = delta < 0.0 ? -double.infinity : math.min(minScrollExtent, pixels); // max 的逻辑是等效的，但反向。 final double max = delta > 0.0 ? double.infinity : math.max(maxScrollExtent, pixels); final double oldPixels = pixels; final double newPixels = (pixels - delta).clamp(min, max) as double; final double clampedDelta = newPixels - pixels; if (clampedDelta == 0.0) { return delta; } final double overScroll = physics.applyBoundaryConditions(this, newPixels); final double actualNewPixels = newPixels - overScroll; final double offset = actualNewPixels - oldPixels; if (offset != 0.0) { forcePixels(actualNewPixels); didUpdateScrollPositionBy(offset); } return delta + offset; } // 返回过度滚动。 double applyFullDragUpdate(double delta) { assert(delta != 0.0); final double oldPixels = pixels; // Apply friction: 施加摩擦： final double newPixels = pixels - physics.applyPhysicsToUserOffset(this, delta); if (oldPixels == newPixels) { // 增量一定很小，我们在添加浮点数时将其删除了 return 0.0; } // Check for overScroll: 检查过度滚动： final double overScroll = physics.applyBoundaryConditions(this, newPixels); final double actualNewPixels = newPixels - overScroll; if (actualNewPixels != oldPixels) { forcePixels(actualNewPixels); didUpdateScrollPositionBy(actualNewPixels - oldPixels); } return overScroll; } @override void beginActivity(ScrollActivity newActivity) { _heldPreviousVelocity = 0.0; if (newActivity == null) { return; } assert(newActivity.delegate == this); super.beginActivity(newActivity); _currentDrag?.dispose(); _currentDrag = null; if (!activity.isScrolling) { updateUserScrollDirection(ScrollDirection.idle); }else{ } } /// 将用户滚动方向设置为给定值。 /// 如果更改了该值，则将分派 [User ScrollNotification]。 @protected @visibleForTesting void updateUserScrollDirection(ScrollDirection value) { assert(value != null); if (userScrollDirection == value) { return; } _userScrollDirection = value; didUpdateScrollDirection(value); } @override ScrollHoldController hold(VoidCallback holdCancelCallback) { final double previousVelocity = activity.velocity; final HoldScrollActivity holdActivity = HoldScrollActivity( delegate: this, onHoldCanceled: holdCancelCallback, ); beginActivity(holdActivity); _heldPreviousVelocity = previousVelocity; return holdActivity; } @override Drag drag(DragStartDetails details, VoidCallback dragCancelCallback) { final ScrollDragController drag = ScrollDragController( delegate: this, details: details, onDragCanceled: dragCancelCallback, carriedVelocity: physics.carriedMomentum(_heldPreviousVelocity), motionStartDistanceThreshold: physics.dragStartDistanceMotionThreshold, ); beginActivity(DragScrollActivity(this, drag)); assert(_currentDrag == null); _currentDrag = drag; return drag; } @override void goIdle() { double velocity = 0; if(activity != null) { if (debugLabel == coordinator.debugLabel) { //主滚动结束,但是有剩余速度 if (activity.velocity != 0) { velocity = activity.velocity; } } else { if (activity.velocity != 0) { velocity = activity.velocity; } } } beginActivity(IdleScrollActivity(this)); if(velocity != 0){ if(debugLabel == coordinator.debugLabel){ // print('主list滚动结束-剩余转子list滚动：$velocity'); coordinator.goBallistic(velocity,scrollInner: true); }else{ // print('子list滚动结束-剩余转主list滚动'); coordinator.goBallistic(velocity); } } } /// 当手指滑动时，该方法会获取到滑动距离。 /// /// [delta] 滑动距离，正增量表示下滑，负增量向上滑。 /// /// 我们需要把子部件的滑动数据交给协调器处理，主部件无干扰。 @override void applyUserOffset(double delta) { coordinator.coordinatorScrolling(); final ScrollDirection userScrollDirection = delta > 0.0 ? ScrollDirection.forward : ScrollDirection.reverse; bool listviewAtTop = pixels == 0; if (debugLabel != coordinator.debugLabel) { //内部滚动 if(userScrollDirection == ScrollDirection.reverse){ //用户向上滑动 return coordinator.applyUserOffset(delta, userScrollDirection, this); }else{ //用户向下滑动 if(listviewAtTop){ return coordinator.applyUserOffset(delta, userScrollDirection, this); } } } updateUserScrollDirection(userScr