Method _trackDestroyedFocusedChip

src/material/chips/chip-set.ts:283–307

Starts tracking the destroyed chips in order to capture the focused one.

()

  /** Starts tracking the destroyed chips in order to capture the focused one. */
  private _trackDestroyedFocusedChip() {
    this.chipDestroyedChanges.pipe(takeUntil(this._destroyed)).subscribe((event: MatChipEvent) => {
      // If the focused chip is destroyed, save its index so that we can move focus to the next
      // chip. We only save the index here, rather than move the focus immediately, because we want
      // to wait until the chip is removed from the chip list before focusing the next one. This
      // allows us to keep focus on the same index if the chip gets swapped out.
      const chipArray = this._chips.toArray();
      const chipIndex = chipArray.indexOf(event.chip);
      const hasFocus = event.chip._hasFocus();
      const wasLastFocused =
        event.chip._hadFocusOnRemove &&
        this._keyManager.activeItem &&
        event.chip._getActions().includes(this._keyManager.activeItem);

      // Note that depending on the timing, the chip might've already lost focus by the
      // time we check this. We need the `wasLastFocused` as a fallback to detect such cases.
      // In `wasLastFocused` we also need to ensure that the chip actually had focus when it was
      // deleted so that we don't steal away the user's focus after they've moved on from the chip.
      const shouldMoveFocus = hasFocus || wasLastFocused;

      if (this._isValidIndex(chipIndex) && shouldMoveFocus) {
        this._lastDestroyedFocusedChipIndex = chipIndex;
      }
    });
  }

  /**
   * Finds the next appropriate chip to move focus to,