public async Task FetchPrePageAtTocNode() { TOCNode currentToc = TOCDataManager.CurrentLeafNode; if (currentToc == null) { return; } while (TOCDataManager.StartTocID != currentToc.ID) { currentToc = PublicationContentUtil.Instance.GetPreviousPageByTreeNode(currentToc); } currentToc = PublicationContentUtil.Instance.GetPreviousPageByTreeNode(currentToc); TOCDataManager.CurrentLeafNode = currentToc; TOCDataManager.StartTocID = currentToc.ID; string htmlString = await PublicationContentUtil.Instance.GetContentFromTOC(BookID, currentToc, false); PageViewController.PrependPageContent(htmlString, BookID, currentToc.ID.ToString(), currentToc.Title); if (currentToc != null) { this.InvokeOnMainThread(() => HighlightLeafTocNode(currentToc) ); } }