Method _updateActiveDropContainer

src/cdk/drag-drop/drag-ref.ts:1107–1167

* Updates the item's position in its drop container, or moves it * into a new one, depending on its current drag position.

({x, y}: Point, {x: rawX, y: rawY}: Point)

   * into a new one, depending on its current drag position.
   */
  private _updateActiveDropContainer({x, y}: Point, {x: rawX, y: rawY}: Point) {
    // Drop container that draggable has been moved into.
    let newContainer = this._initialContainer._getSiblingContainerFromPosition(this, x, y);

    // If we couldn't find a new container to move the item into, and the item has left its
    // initial container, check whether the it's over the initial container. This handles the
    // case where two containers are connected one way and the user tries to undo dragging an
    // item into a new container.
    if (
      !newContainer &&
      this._dropContainer !== this._initialContainer &&
      this._initialContainer._isOverContainer(x, y)
    ) {
      newContainer = this._initialContainer;
    }

    if (newContainer && newContainer !== this._dropContainer) {
      this._ngZone.run(() => {
        const exitIndex = this._dropContainer!.getItemIndex(this);
        const nextItemElement =
          this._dropContainer!.getItemAtIndex(exitIndex + 1)?.getVisibleElement() || null;

        // Notify the old container that the item has left.
        this.exited.next({item: this, container: this._dropContainer!});
        this._dropContainer!.exit(this);
        this._conditionallyInsertAnchor(newContainer, this._dropContainer!, nextItemElement);
        // Notify the new container that the item has entered.
        this._dropContainer = newContainer!;
        this._dropContainer.enter(
          this,
          x,
          y,
          // If we're re-entering the initial container and sorting is disabled,
          // put item the into its starting index to begin with.
          newContainer === this._initialContainer && newContainer.sortingDisabled
            ? this._initialIndex
            : undefined,
        );
        this.entered.next({
          item: this,
          container: newContainer!,
          currentIndex: newContainer!.getItemIndex(this),
        });
      });
    }

    // Dragging may have been interrupted as a result of the events above.
    if (this.isDragging()) {
      this._dropContainer!._startScrollingIfNecessary(rawX, rawY);
      this._dropContainer!._sortItem(this, x, y, this._pointerDirectionDelta);

      if (this.constrainPosition) {
        this._applyPreviewTransform(x, y);
      } else {
        this._applyPreviewTransform(
          x - this._pickupPositionInElement.x,
          y - this._pickupPositionInElement.y,
        );