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FixedSizeList.js
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FixedSizeList.js
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// @flow
import createListComponent from './createListComponent';
import type { Props, ScrollToAlign } from './createListComponent';
type InstanceProps = any;
const FixedSizeList = createListComponent({
getItemOffset: ({ itemSize }: Props<any>, index: number): number =>
index * ((itemSize: any): number),
getItemSize: ({ itemSize }: Props<any>, index: number): number =>
((itemSize: any): number),
getEstimatedTotalSize: ({ itemCount, itemSize }: Props<any>) =>
((itemSize: any): number) * itemCount,
getOffsetForIndexAndAlignment: (
{ direction, height, itemCount, itemSize, layout, width }: Props<any>,
index: number,
align: ScrollToAlign,
scrollOffset: number,
instanceProps: InstanceProps,
scrollbarSize: number
): number => {
// TODO Deprecate direction "horizontal"
const isHorizontal = direction === 'horizontal' || layout === 'horizontal';
const size = (((isHorizontal ? width : height): any): number);
const lastItemOffset = Math.max(
0,
itemCount * ((itemSize: any): number) - size
);
const maxOffset = Math.min(
lastItemOffset,
index * ((itemSize: any): number)
);
const minOffset = Math.max(
0,
index * ((itemSize: any): number) -
size +
((itemSize: any): number) +
scrollbarSize
);
if (align === 'smart') {
if (
scrollOffset >= minOffset - size &&
scrollOffset <= maxOffset + size
) {
align = 'auto';
} else {
align = 'center';
}
}
switch (align) {
case 'start':
return maxOffset;
case 'end':
return minOffset;
case 'center': {
// "Centered" offset is usually the average of the min and max.
// But near the edges of the list, this doesn't hold true.
const middleOffset = Math.round(
minOffset + (maxOffset - minOffset) / 2
);
if (middleOffset < Math.ceil(size / 2)) {
return 0; // near the beginning
} else if (middleOffset > lastItemOffset + Math.floor(size / 2)) {
return lastItemOffset; // near the end
} else {
return middleOffset;
}
}
case 'auto':
default:
if (scrollOffset >= minOffset && scrollOffset <= maxOffset) {
return scrollOffset;
} else if (scrollOffset < minOffset) {
return minOffset;
} else {
return maxOffset;
}
}
},
getStartIndexForOffset: (
{ itemCount, itemSize }: Props<any>,
offset: number
): number =>
Math.max(
0,
Math.min(itemCount - 1, Math.floor(offset / ((itemSize: any): number)))
),
getStopIndexForStartIndex: (
{ direction, height, itemCount, itemSize, layout, width }: Props<any>,
startIndex: number,
scrollOffset: number
): number => {
// TODO Deprecate direction "horizontal"
const isHorizontal = direction === 'horizontal' || layout === 'horizontal';
const offset = startIndex * ((itemSize: any): number);
const size = (((isHorizontal ? width : height): any): number);
const numVisibleItems = Math.ceil(
(size + scrollOffset - offset) / ((itemSize: any): number)
);
return Math.max(
0,
Math.min(
itemCount - 1,
startIndex + numVisibleItems - 1 // -1 is because stop index is inclusive
)
);
},
initInstanceProps(props: Props<any>): any {
// Noop
},
shouldResetStyleCacheOnItemSizeChange: true,
validateProps: ({ itemSize }: Props<any>): void => {
if (process.env.NODE_ENV !== 'production') {
if (typeof itemSize !== 'number') {
throw Error(
'An invalid "itemSize" prop has been specified. ' +
'Value should be a number. ' +
`"${itemSize === null ? 'null' : typeof itemSize}" was specified.`
);
}
}
},
});
export default FixedSizeList;