Function createImperativeHandle

src/utils/createImperativeHandle.ts:48–310

(ctx: StateContext, scheduleImperativeScrollCommit?: () => void)

}

export function createImperativeHandle(ctx: StateContext, scheduleImperativeScrollCommit?: () => void): LegendListRef {
    const state = ctx.state;
    const IMPERATIVE_SCROLL_SETTLE_MAX_WAIT_MS = 800;
    const IMPERATIVE_SCROLL_SETTLE_STABLE_FRAMES = 2;
    let imperativeScrollToken = 0;

    const isSettlingAfterDataChange = () =>
        !!state.didDataChange ||
        !!state.didColumnsChange ||
        state.queuedMVCPRecalculate !== undefined ||
        state.ignoreScrollFromMVCP !== undefined;

    const isScrollToIndexReady = (targetIndex: number, allowEmpty = false) => {
        const props = state.props;
        const dataLength = props.data.length;
        const anchorIndex = props.anchoredEndSpace?.anchorIndex;

        if (targetIndex < 0) {
            return allowEmpty;
        }
        if (targetIndex >= dataLength) {
            return false;
        }
        if (anchorIndex === undefined || anchorIndex < 0 || anchorIndex >= dataLength || targetIndex < anchorIndex) {
            return true;
        }

        return areKnownOrFixedItemSizesAvailable(ctx, anchorIndex, dataLength - 1);
    };

    const runWhenReady = (token: number, run: () => void, isReady: () => boolean) => {
        const startedAt = Date.now();
        let stableFrames = 0;

        const check = () => {
            if (token !== imperativeScrollToken) {
                return;
            }

            if (isSettlingAfterDataChange() || !isReady()) {
                stableFrames = 0;
            } else {
                stableFrames += 1;
            }

            const timedOut = Date.now() - startedAt >= IMPERATIVE_SCROLL_SETTLE_MAX_WAIT_MS;
            if (stableFrames >= IMPERATIVE_SCROLL_SETTLE_STABLE_FRAMES || timedOut) {
                run();
                return;
            }

            requestAnimationFrame(check);
        };

        requestAnimationFrame(check);
    };

    const runScrollRequest = (token: number, resolve: () => void, run: () => boolean, isReady = () => true) => {