HarmonyOS Next开发----k线图滑动惯性

K线图的惯性滑动，由于官方提供的Scroller没有设置初始位置的方法，不知道后面会不会支持。由于项目急着上线，所以只有采用另一种方案，滑动结束后模拟计算惯性滑动。

思路：

手指滑动结束后，k线惯性滑动轨迹，类似于匀减速运动。所以可以用个定时器，每个100ms让k线继续平移一段距离，只需要计算出每个时刻的速度即可。对于手指离开屏幕时的速度，可以用平均速度来代替。

class SlideInertia {public callback?: (x: number | null) => void;private startX: number = 0;private lastMoveX: number = 0;private velocity: number = 0;private startTime: number = 0;private timerId: number = -1;constructor(callback?: (x: number | null) => void) {this.callback = callback}public handleTouchStart = (event: GestureEvent) => {this.startX = event.offsetX;this.startTime = new Date().getTime();};public handleTouchMove = (event: GestureEvent) => {this.lastMoveX = event.offsetX;};public handleTouchEnd = () => {const curTime = new Date().getTime();const diffTime = (curTime - this.startTime) / 10;if (diffTime <= 0) {return;}this.velocity = (this.startX - this.lastMoveX) / diffTime;// 释放触摸，开始惯性滑动this.startFling();this.startTime = 0;};private startFling() {const step = () => {this.velocity *= 0.9; // 惯性减弱if (Math.abs(this.velocity) > 1) {if (this.callback) {this.callback(this.velocity);}this.timerId = setTimeout(step, 100);} else {if (this.callback) {this.callback(null);}}};this.timerId = setTimeout(step);}public clearTimer() {if (this.timerId > 0) {clearTimeout(this.timerId);}}
}

然后在组件的TouchDown、TouchMove和TouchUP事件处调用，然后回调里面处理滑动即可。

 .onActionStart((event) => {if (!this.mIsTouchRegionStats && !this.mIsLongPressed && event.fingerList.length === 1) {this.requestParentNotHandleGesture(true);this.mGestureHelper.startScroll();this.slideInertia.handleTouchStart(event);}}).onActionEnd(() => {this.mGestureHelper.stopScroll();this.onDraw();}).onActionUpdate((event?: GestureEvent) => {if (event && event.fingerList.length === 1) {if (this.mIsLongPressed) {let reallyOffsetX: number = event.offsetX - this.mLastOffsetX;let reallyOffsetY: number = event.offsetY - this.mLastOffsetY;this.mLastOffsetX = event.offsetX;this.mLastOffsetY = event.offsetY;this.mTouchPoint.offset(reallyOffsetX, reallyOffsetY);let mainRenderTitleHeight = this.titleHeightArr[0];const padding = UPMarketUIIndexBaseRender.padding;this.mTouchPoint.y = Math.max(mainRenderTitleHeight + padding, this.mTouchPoint.y);this.mTouchPoint.y = Math.min(this.totalHeight - padding * 2, this.mTouchPoint.y);this.mGestureHelper.updateCrossPoint(this.touchX2CrossX(this.mTouchPoint.x), this.mTouchPoint.y);this.callbackLongClickData();this.onDraw();} else if (!this.mGestureHelper.isShowCross()) {//平移if (this.mGestureHelper.scroll(event.offsetX, this.totalWidth)) {this.callbackRegionStatsChanged();this.onDraw();}this.slideInertia.handleTouchMove(event);}}}})

   .onTouch((event: TouchEvent) => {switch (event.type) {case TouchType.Down:this.slideInertia.clearTimer();this.mIsTouchRegionStats = this.mGestureHelper.isTouchRegionStatsControlPoint(new UPPoint(event.touches[0].x, event.touches[0].y));if (this.mIsTouchRegionStats) {this.requestParentNotHandleGesture(true);}this.mLastTouchDownPoint.set(event.touches[0].x, event.touches[0].y);breakcase TouchType.Move:let distanceX: number = Math.abs(this.mLastTouchDownPoint.x - event.touches[0].x);let distanceY: number = Math.abs(this.mLastTouchDownPoint.y - event.touches[0].y);if ((distanceX > distanceY && (this.attrs?.supportTranslationAndZoom || this.mIsLongPressed))|| this.mIsTouchRegionStats) { // 如果触摸点在区间统计控制区域，则支持垂直和水平方向滑动，无需判断distanceXthis.mCanHorizontalScroll = true;}if (this.mIsTouchRegionStats) {let regionStatsIndexChanged = this.mGestureHelper.updateRegionStatsControlPoint(new UPPoint(event.touches[0].x, event.touches[0].y), event.touches[0].x - this.mLastTouchDownPoint.x);if (regionStatsIndexChanged) {this.callbackRegionStatsChanged();this.onDraw();}}breakcase TouchType.Up:case TouchType.Cancel:if (!this.mGestureHelper.isShowRegionStats() && !this.mIsLongPressed) {this.slideInertia.handleTouchEnd();}

由于k线图有些操作时不需要惯性滑动的(比如长按、区间统计打开时等)，所以将handleTouchStart和handleTouchMove放在了平移手势回调里面。

  private slideInertia: SlideInertia = new SlideInertia((offsetX: number | null) => {if (offsetX == null) {return;}if (this.mGestureHelper.scroll(0, 0, Math.floor(offsetX))) {this.onDraw();} else {this.slideInertia.clearTimer();}});