添加项目并滚动到它——筛选标签模式
用户选择一个筛选器时,标签栏会增长,而新标签应当出现在屏幕上,而不是藏在右边缘之外。难点在于:你无法滚动到一个尚未渲染的元素。此示例把工作拆分为一个点击处理器和一个副作用。
点击添加筛选器——标签出现在末尾,这一行滚动以把它显示出来。点 x 可移除标签。
工作原理
菜单接收到一个 apiRef,它在组件树之外暴露完整 API。addItem 做两件事:把新 id 存入 lastAdded 这个 ref,然后把项目追加到 state。它有意不去滚动——此刻标签还只是 state,不是 DOM。
为什么滚动放在副作用里
getItemElementById 会在 DOM 中查找项目,因此滚动只能在 React 提交新项目之后发生。一个以 items 为依赖的 useEffect 恰好在此时运行:它读取 lastAdded、清除它,然后调用 apiRef.current.scrollToItem(el, ’smooth’, ’end’)。清除 ref 很重要——任何其他原因(选中、箭头)引起的重新渲染也会触达该副作用,绝不能再次滚动。
注意
lastAdded是 ref,不是 state:写入它本身不应触发渲染,其值只对紧随其后的那次副作用有意义。’end’让新标签对齐这一行的右边缘;如果你想让它位于中间,’center’的工作方式相同。- 这里的箭头使用
useLeftArrowVisible()与useRightArrowVisible()这两个 hook——是useIsVisible(’first’/’last’)这一对的更简写法。 - 滚动条通过库的
scroll-container类上的普通 CSS 来隐藏;滚动本身仍是原生的。
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 AddItemAndScrollToItExample() {
const [items, setItems] = React.useState(() => getItems());
const [selected, setSelected] = React.useState<string[]>([]);
const isItemSelected = (id: string): boolean =>
!!selected.find((el) => el === id);
const handleItemClick = (itemId: string) => {
const itemSelected = isItemSelected(itemId);
setSelected((currentSelected: string[]) =>
itemSelected
? currentSelected.filter((el) => el !== itemId)
: currentSelected.concat(itemId),
);
};
const apiRef = React.useRef<publicApiType>(null);
// The id of the item added by the last click; empty on mount and after the
// scroll fires, so re-renders for other reasons don't scroll again.
const lastAdded = React.useRef<string | null>(null);
const addItem = () => {
const newId = getId(items.length);
lastAdded.current = newId;
setItems((currentItems) => currentItems.concat({ id: newId }));
};
// `getItemElementById` looks the item up in the DOM, so the scroll can only
// happen after React has rendered the new item — an effect keyed on `items`
// rather than a call inside the click handler.
React.useEffect(() => {
const newId = lastAdded.current;
if (!newId) {
return;
}
lastAdded.current = null;
const el = apiRef.current?.getItemElementById(newId);
if (el) {
apiRef.current?.scrollToItem(el, 'smooth', 'end');
}
}, [items]);
return (
<div>
<div>
<button onClick={addItem} data-testid="add-item">
Add item
</button>
</div>
<NoScrollbar>
<ScrollMenu
LeftArrow={LeftArrow}
RightArrow={RightArrow}
onWheel={onWheel}
apiRef={apiRef}
>
{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>
</div>
);
}
export default AddItemAndScrollToItExample;
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();
}
}