用鼠标拖拽滚动——而不破坏点击
触摸用户原生就能滚动横向列表,但鼠标用户需要接线:按住、拖拽、松开。难点不在于移动这一行——而在于一个天真的实现会把每次松开拖拽都变成一次意外的项目点击。此示例用一个小型
DragDealer 类和三个鼠标属性把二者分开。按住这一行任意位置拖拽。项目仍可点击——拖拽之后的点击会被抑制。
工作原理
ScrollMenu 暴露了柯里化的鼠标处理器——onMouseDown、onMouseUp 与 onMouseMove 各自接收 API 对象并返回一个普通的事件处理器。DragDealer 实例跟踪一个锚点坐标:每次移动时把增量直接应用到 scrollContainer.current.scrollLeft。剩下的交给原生滚动——没有变换、没有物理,滚动条也依然真实。
为什么点击仍能生效
只有当指针移动超过 5px 时,拖拽才会开始,因此普通点击绝不会触发滚动。另一个方向是经典 bug:项目的 onClick 在 mouseup 之后触发,所以在卡片上方松开拖拽会选中它。dragStop 立即清除 applying 标志,但再保留 dragging 一帧——点击处理器检查它并退出。
值得借鉴的细节
dragStart会取消上一次手势遗留的待处理重置——没有它,快速的第二次拖拽可能应用过期的增量。- 包装器上的
onMouseLeave也会调用dragStop,这样拖拽中途离开这一行也不会让拖拽状态卡住。 - 触摸完全不需要这些——容器是真正的滚动容器,滑动本身就能滚动。
完整源码
完整且可直接复制粘贴——这正是背后这份文件的 可在 Storybook 中实时编辑的版本.
import 'react-horizontal-scrolling-menu/dist/styles.css';
import styled from '@emotion/styled';
import React from 'react';
import {
type publicApiType,
ScrollMenu,
VisibilityContext,
} from 'react-horizontal-scrolling-menu';
export function MouseDrag() {
const [items] = React.useState(() => getItems());
const [selected, setSelected] = React.useState<string[]>([]);
// NOTE: for drag by mouse
const dragState = React.useRef(new DragDealer());
const handleDrag =
({ scrollContainer }: publicApiType) =>
(ev: React.MouseEvent) =>
dragState.current.dragMove(ev, (posDiff) => {
if (scrollContainer.current) {
scrollContainer.current.scrollLeft += posDiff;
}
});
const onMouseDown = React.useCallback(
() => dragState.current.dragStart,
[dragState],
);
const onMouseUp = React.useCallback(
() => dragState.current.dragStop,
[dragState],
);
const isItemSelected = (id: string): boolean =>
!!selected.find((el) => el === id);
const handleItemClick = (itemId: string) => {
if (dragState.current.dragging) {
return false;
}
const itemSelected = isItemSelected(itemId);
setSelected((currentSelected: string[]) =>
itemSelected
? currentSelected.filter((el) => el !== itemId)
: currentSelected.concat(itemId),
);
};
return (
<NoScrollbar onMouseLeave={() => dragState.current.dragStop()}>
<ScrollMenu
LeftArrow={LeftArrow}
RightArrow={RightArrow}
onMouseDown={onMouseDown}
onMouseUp={onMouseUp}
onMouseMove={handleDrag}
onWheel={onWheel}
>
{items.map(({ id }) => (
<Card
title={id}
itemId={id} // NOTE: itemId is required for track items
key={id}
onClick={() => handleItemClick(id)}
selected={isItemSelected(id)}
/>
))}
</ScrollMenu>
</NoScrollbar>
);
}
export default MouseDrag;
class DragDealer {
clicked: boolean;
dragging: boolean;
position: number;
constructor() {
this.clicked = false;
this.dragging = false;
this.position = 0;
}
public dragStart = (ev: React.MouseEvent) => {
this.position = ev.clientX;
this.clicked = true;
};
public dragStop = () => {
window.requestAnimationFrame(() => {
this.dragging = false;
this.clicked = false;
});
};
public dragMove = (ev: React.MouseEvent, cb: (posDiff: number) => void) => {
const newDiff = this.position - ev.clientX;
const movedEnough = Math.abs(newDiff) > 5;
if (this.clicked && movedEnough) {
this.dragging = true;
}
if (this.dragging && movedEnough) {
this.position = ev.clientX;
cb(newDiff);
}
};
}
const NoScrollbar = styled('div')({
'& .react-horizontal-scrolling-menu--scroll-container::-webkit-scrollbar': {
display: 'none',
},
'& .react-horizontal-scrolling-menu--scroll-container': {
scrollbarWidth: 'none',
'-ms-overflow-style': 'none',
},
});
function LeftArrow() {
const visibility = React.useContext<publicApiType>(VisibilityContext);
const disabled = visibility.useLeftArrowVisible();
return (
<Arrow
disabled={disabled}
onClick={() => visibility.scrollPrev()}
testId="left-arrow"
>
Left
</Arrow>
);
}
function RightArrow() {
const visibility = React.useContext<publicApiType>(VisibilityContext);
const disabled = visibility.useRightArrowVisible();
return (
<Arrow
disabled={disabled}
onClick={() => visibility.scrollNext()}
testId="right-arrow"
>
Right
</Arrow>
);
}
function Arrow({
children,
disabled,
onClick,
className,
testId,
}: {
children: React.ReactNode;
disabled: boolean;
onClick: VoidFunction;
className?: string;
testId: string;
}) {
return (
<ArrowButton
disabled={disabled}
onClick={onClick}
className={'arrow' + `-${className}`}
data-testid={testId}
>
{children}
</ArrowButton>
);
}
const ArrowButton = styled('button')((props) => ({
cursor: 'pointer',
display: 'flex',
flexDirection: 'column',
justifyContent: 'center',
marginBottom: '2px',
opacity: props.disabled ? '0' : '1',
userSelect: 'none',
borderRadius: '6px',
borderWidth: '1px',
}));
function Card({
onClick,
selected,
title,
itemId,
}: {
onClick: (context: publicApiType) => void;
selected: boolean;
title: string;
itemId: string;
}) {
const visibility = React.useContext<publicApiType>(VisibilityContext);
const isVisible = visibility.useIsVisible(itemId, true);
return (
<CardBody
data-cy={itemId}
onClick={() => onClick(visibility)}
onKeyDown={(ev: React.KeyboardEvent) => {
ev.code === 'Enter' && onClick(visibility);
}}
data-testid="card"
role="button"
tabIndex={0}
className="card"
visible={isVisible}
selected={selected}
>
<div className="header">
<div>{title}</div>
<div className="visible">visible: {JSON.stringify(isVisible)}</div>
<div className="selected">selected: {JSON.stringify(!!selected)}</div>
</div>
<div className="background" />
</CardBody>
);
}
const CardBody = styled('div')<{ selected?: boolean; visible?: boolean }>(
(props) => ({
border: '1px solid',
display: 'inline-block',
margin: '0 10px',
width: '160px',
userSelect: 'none',
borderRadius: '8px',
overflow: 'hidden',
'& .header': {
backgroundColor: 'white',
},
'& .visible': {
backgroundColor: props.visible ? 'transparent' : 'gray',
},
'& .background': {
backgroundColor: props.selected ? 'green' : 'bisque',
height: '200px',
},
}),
);
const getId = (index: number) => `${'test'}${index}`;
const getItems = () =>
Array(10)
.fill(0)
.map((_, ind) => ({ id: getId(ind) }));
function onWheel(apiObj: publicApiType, ev: React.WheelEvent): void {
// NOTE: no good standart way to distinguish touchpad scrolling gestures
// but can assume that gesture will affect X axis, mouse scroll only Y axis
// of if deltaY too small probably is it touchpad
const isThouchpad = Math.abs(ev.deltaX) !== 0 || Math.abs(ev.deltaY) < 15;
if (isThouchpad) {
ev.stopPropagation();
return;
}
if (ev.deltaY < 0) {
apiObj.scrollNext();
} else {
apiObj.scrollPrev();
}
}