292 lines
10 KiB
Dart
292 lines
10 KiB
Dart
import 'dart:math' as math;
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import 'package:flutter/gestures.dart';
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import 'package:flutter/physics.dart';
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import 'package:flutter/rendering.dart';
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import 'package:flutter/widgets.dart';
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import 'shop_scroll_coordinator.dart';
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/// 滑动位置信息
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class ShopScrollPosition extends ScrollPosition
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implements ScrollActivityDelegate {
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final ShopScrollCoordinator coordinator; // 协调器
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ScrollDragController _currentDrag;
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double _heldPreviousVelocity = 0.0;
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ShopScrollPosition(
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{@required ScrollPhysics physics,
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@required ScrollContext context,
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double initialPixels = 0.0,
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bool keepScrollOffset = true,
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ScrollPosition oldPosition,
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String debugLabel,
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@required this.coordinator})
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: super(
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physics: physics,
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context: context,
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keepScrollOffset: keepScrollOffset,
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oldPosition: oldPosition,
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debugLabel: debugLabel,
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) {
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// 如果oldPosition不为null，则父级将首先调用Absorb()，它可以设置_pixels和_activity.
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if (!hasPixels && initialPixels != null) correctPixels(initialPixels);
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if (activity == null) goIdle();
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assert(activity != null);
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}
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@override
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AxisDirection get axisDirection => context.axisDirection;
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@override
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double setPixels(double newPixels) {
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assert(activity.isScrolling);
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return super.setPixels(newPixels);
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}
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@override
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void absorb(ScrollPosition other) {
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super.absorb(other);
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if (other is! ScrollPositionWithSingleContext) {
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goIdle();
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return;
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}
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activity.updateDelegate(this);
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final ShopScrollPosition typedOther = other as ShopScrollPosition;
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_userScrollDirection = typedOther._userScrollDirection;
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assert(_currentDrag == null);
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if (typedOther._currentDrag != null) {
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_currentDrag = typedOther._currentDrag;
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_currentDrag.updateDelegate(this);
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typedOther._currentDrag = null;
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}
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}
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@override
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void applyNewDimensions() {
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super.applyNewDimensions();
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context.setCanDrag(physics.shouldAcceptUserOffset(this));
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}
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/// 返回未使用的增量。
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/// 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）。
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double applyClampedDragUpdate(double delta) {
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assert(delta != 0.0);
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// 如果我们要朝向maxScrollExtent（负滚动偏移），那么我们在minScrollExtent方向上
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// 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。
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// 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
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// 上可以达到的最大距离是我们现在所处的位置（如果我们已经过度滚动）
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// （在这种情况下，像素小于minScrollExtent），或者如果minScrollExtent可以 我们不是。
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// 换句话说，我们不能通过applyClampedDragUpdate进入过滚动状态。
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// 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
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// applyFullDragUpdate（请参见下文）。也可能会发生过度滚动的情况，例如 如果使用滚动控制器人工设置了滚动位置。
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final double min =
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delta < 0.0 ? -double.infinity : math.min(minScrollExtent, pixels);
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// max的逻辑是等效的，但反向。
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final double max =
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delta > 0.0 ? double.infinity : math.max(maxScrollExtent, pixels);
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final double oldPixels = pixels;
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final double newPixels = (pixels - delta).clamp(min, max) as double;
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final double clampedDelta = newPixels - pixels;
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if (clampedDelta == 0.0) return delta;
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final double overScroll = physics.applyBoundaryConditions(this, newPixels);
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final double actualNewPixels = newPixels - overScroll;
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final double offset = actualNewPixels - oldPixels;
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if (offset != 0.0) {
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forcePixels(actualNewPixels);
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didUpdateScrollPositionBy(offset);
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}
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return delta + offset;
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}
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// Returns the overScroll. 返回过度滚动。
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double applyFullDragUpdate(double delta) {
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assert(delta != 0.0);
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final double oldPixels = pixels;
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// Apply friction: 施加摩擦：
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final double newPixels =
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pixels - physics.applyPhysicsToUserOffset(this, delta);
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if (oldPixels == newPixels) return 0.0; // 增量一定很小，我们在添加浮点数时将其删除了
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// Check for overScroll: 检查过度滚动：
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final double overScroll = physics.applyBoundaryConditions(this, newPixels);
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final double actualNewPixels = newPixels - overScroll;
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if (actualNewPixels != oldPixels) {
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forcePixels(actualNewPixels);
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didUpdateScrollPositionBy(actualNewPixels - oldPixels);
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}
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return overScroll;
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}
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/// 当手指滑动时，该方法会获取到滑动距离
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/// [delta]滑动距离，正增量表示下滑，负增量向上滑
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/// 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
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@override
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void applyUserOffset(double delta) {
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ScrollDirection userScrollDirection =
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delta > 0.0 ? ScrollDirection.forward : ScrollDirection.reverse;
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if (debugLabel != coordinator.pageLabel)
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return coordinator.applyUserOffset(delta, userScrollDirection, this);
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updateUserScrollDirection(userScrollDirection);
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setPixels(pixels - physics.applyPhysicsToUserOffset(this, delta));
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}
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@override
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void beginActivity(ScrollActivity newActivity) {
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_heldPreviousVelocity = 0.0;
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if (newActivity == null) return;
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assert(newActivity.delegate == this);
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super.beginActivity(newActivity);
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_currentDrag?.dispose();
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_currentDrag = null;
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if (!activity.isScrolling) updateUserScrollDirection(ScrollDirection.idle);
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}
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/// 将[用户滚动方向]设置为给定值。
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/// 如果更改了该值，则将分派[User ScrollNotification]。
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@protected
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@visibleForTesting
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void updateUserScrollDirection(ScrollDirection value) {
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assert(value != null);
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if (userScrollDirection == value) return;
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_userScrollDirection = value;
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didUpdateScrollDirection(value);
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}
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@override
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ScrollHoldController hold(VoidCallback holdCancelCallback) {
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final double previousVelocity = activity.velocity;
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final HoldScrollActivity holdActivity =
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HoldScrollActivity(delegate: this, onHoldCanceled: holdCancelCallback);
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beginActivity(holdActivity);
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_heldPreviousVelocity = previousVelocity;
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return holdActivity;
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}
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@override
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Drag drag(DragStartDetails details, VoidCallback dragCancelCallback) {
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final ScrollDragController drag = ScrollDragController(
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delegate: this,
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details: details,
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onDragCanceled: dragCancelCallback,
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carriedVelocity: physics.carriedMomentum(_heldPreviousVelocity),
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motionStartDistanceThreshold: physics.dragStartDistanceMotionThreshold,
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);
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beginActivity(DragScrollActivity(this, drag));
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assert(_currentDrag == null);
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_currentDrag = drag;
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return drag;
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}
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@override
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void goIdle() {
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beginActivity(IdleScrollActivity(this));
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}
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/// 以特定的速度开始一个物理驱动的模拟，该模拟确定[pixels]位置。
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/// 此方法遵从[ScrollPhysics.createBallisticSimulation]，该方法通常在当前位置超出
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/// 范围时提供滑动模拟，而在当前位置超出范围但具有非零速度时提供摩擦模拟。
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/// 速度应以每秒逻辑像素为单位。
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@override
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void goBallistic(double velocity, [bool fromCoordinator = false]) {
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if (debugLabel != coordinator.pageLabel) {
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if (velocity > 0.0) coordinator.goBallistic(velocity);
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} else {
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if (fromCoordinator && velocity <= 0.0) return;
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if (coordinator.pageExpand == PageExpandState.Expanding) return;
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}
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assert(pixels != null);
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final Simulation simulation =
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physics.createBallisticSimulation(this, velocity);
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if (simulation != null) {
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beginActivity(BallisticScrollActivity(this, simulation, context.vsync));
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} else {
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goIdle();
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}
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}
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@override
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bool applyContentDimensions(double minScrollExtent, double maxScrollExtent,
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[bool fromCoordinator = false]) {
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if (debugLabel == coordinator.pageLabel && !fromCoordinator)
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return coordinator.applyContentDimensions(
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minScrollExtent, maxScrollExtent, this);
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return super.applyContentDimensions(minScrollExtent, maxScrollExtent);
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}
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@override
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ScrollDirection get userScrollDirection => _userScrollDirection;
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ScrollDirection _userScrollDirection = ScrollDirection.idle;
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@override
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Future<void> animateTo(
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double to, {
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@required Duration duration,
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@required Curve curve,
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}) {
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if (nearEqual(to, pixels, physics.tolerance.distance)) {
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// 跳过动画，直接移到我们已经靠近的位置。
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jumpTo(to);
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return Future<void>.value();
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}
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final DrivenScrollActivity activity = DrivenScrollActivity(
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this,
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from: pixels,
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to: to,
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duration: duration,
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curve: curve,
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vsync: context.vsync,
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);
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beginActivity(activity);
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return activity.done;
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}
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@override
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void jumpTo(double value) {
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goIdle();
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if (pixels != value) {
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final double oldPixels = pixels;
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forcePixels(value);
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notifyListeners();
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didStartScroll();
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didUpdateScrollPositionBy(pixels - oldPixels);
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didEndScroll();
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}
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goBallistic(0.0);
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}
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@Deprecated('This will lead to bugs.')
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@override
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void jumpToWithoutSettling(double value) {
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goIdle();
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if (pixels != value) {
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final double oldPixels = pixels;
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forcePixels(value);
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notifyListeners();
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didStartScroll();
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didUpdateScrollPositionBy(pixels - oldPixels);
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didEndScroll();
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}
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}
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@override
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void dispose() {
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_currentDrag?.dispose();
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_currentDrag = null;
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super.dispose();
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}
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@override
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void debugFillDescription(List<String> description) {
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super.debugFillDescription(description);
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description.add('${context.runtimeType}');
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description.add('$physics');
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description.add('$activity');
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description.add('$userScrollDirection');
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}
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@override
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void pointerScroll(double delta) {
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// TODO: implement pointerScroll
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}
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} |