Method _measureRangeSize

src/cdk/table/table.ts:1610–1649

* Measures the size of the rendered range in the table. * This is used for virtual scrolling when auto-sizing is enabled.

(range: ListRange, orientation: 'horizontal' | 'vertical')

   * This is used for virtual scrolling when auto-sizing is enabled.
   */
  private _measureRangeSize(range: ListRange, orientation: 'horizontal' | 'vertical'): number {
    if (range.start >= range.end || orientation !== 'vertical') {
      return 0;
    }

    const renderedRange = this.viewChange.value;
    const viewContainerRef = this._rowOutlet.viewContainer;

    if (
      (range.start < renderedRange.start || range.end > renderedRange.end) &&
      (typeof ngDevMode === 'undefined' || ngDevMode)
    ) {
      throw Error(`Error: attempted to measure an item that isn't rendered.`);
    }

    const renderedStartIndex = range.start - renderedRange.start;
    const rangeLen = range.end - range.start;
    let firstNode: HTMLElement | undefined;
    let lastNode: HTMLElement | undefined;

    for (let i = 0; i < rangeLen; i++) {
      const view = viewContainerRef.get(i + renderedStartIndex) as EmbeddedViewRef<unknown> | null;
      if (view && view.rootNodes.length) {
        firstNode = lastNode = view.rootNodes[0];
        break;
      }
    }

    for (let i = rangeLen - 1; i > -1; i--) {
      const view = viewContainerRef.get(i + renderedStartIndex) as EmbeddedViewRef<unknown> | null;
      if (view && view.rootNodes.length) {
        lastNode = view.rootNodes[view.rootNodes.length - 1];
        break;
      }
    }

    const startRect = firstNode?.getBoundingClientRect?.();
    const endRect = lastNode?.getBoundingClientRect?.();
    return startRect && endRect ? endRect.bottom - startRect.top : 0;
  }

  private _virtualScrollEnabled(): boolean {
    return !this._disableVirtualScrolling && this._virtualScrollViewport != null;