Method _applyChanges

packages/common/src/directives/ng_for_of.ts:286–325

(changes: IterableChanges<T>)

  }

  private _applyChanges(changes: IterableChanges<T>) {
    const viewContainer = this._viewContainer;
    changes.forEachOperation(
      (
        item: IterableChangeRecord<T>,
        adjustedPreviousIndex: number | null,
        currentIndex: number | null,
      ) => {
        if (item.previousIndex == null) {
          // NgForOf is never "null" or "undefined" here because the differ detected
          // that a new item needs to be inserted from the iterable. This implies that
          // there is an iterable value for "_ngForOf".
          viewContainer.createEmbeddedView(
            this._template,
            new NgForOfContext<T, U>(item.item, this._ngForOf!, -1, -1),
            currentIndex === null ? undefined : currentIndex,
          );
        } else if (currentIndex == null) {
          viewContainer.remove(adjustedPreviousIndex === null ? undefined : adjustedPreviousIndex);
        } else if (adjustedPreviousIndex !== null) {
          const view = viewContainer.get(adjustedPreviousIndex)!;
          viewContainer.move(view, currentIndex);
          applyViewChange(view as EmbeddedViewRef<NgForOfContext<T, U>>, item);
        }
      },
    );

    for (let i = 0, ilen = viewContainer.length; i < ilen; i++) {
      const viewRef = <EmbeddedViewRef<NgForOfContext<T, U>>>viewContainer.get(i);
      const context = viewRef.context;
      context.index = i;
      context.count = ilen;
      context.ngForOf = this._ngForOf!;
    }

    changes.forEachIdentityChange((record: any) => {
      const viewRef = <EmbeddedViewRef<NgForOfContext<T, U>>>viewContainer.get(record.currentIndex);
      applyViewChange(viewRef, record);
    });
  }

  /**
   * Asserts the correct type of the context for the template that `NgForOf` will render.