swift - Tableview 插入行跳动

Question

我已经在 TableView 中实现了 insertRows 方法。如果我在 tableView 插入新行时向下滚动或滚动到 tableView 内容的底部，则整个表格会发生跳跃并将我置于 tableview 内容中的不同位置。我该如何解决？我已在底部添加了我的代码:

//Method to load more data
func loadMoreFeed() {
    let rowsBefore = self.tableObjects.count
    loadMoreFeedInBackground() { queryObjects in
        for object in queryObjects! {
            self.tableObjects.append(object)
        }

        self.tableObjects.sort {
            $0.date!.compare($1.date!) == .orderedDescending 
        }

        let rowsAfter = self.tableObjects.count
        var indexPaths = [IndexPath]()

        for i in 0 ... (rowsAfter - rowsBefore - 1){ //start i at zero and go up to the difference - 1
            indexPaths.append(IndexPath(row: rowsBefore + i, section: 0)) //insert an index path in the array
        }

        self.isMoreDataLoading = false
        self.loadingMoreView!.stopAnimating()

        self.tableView.beginUpdates()
        self.tableView.insertRows(at: indexPaths, with: .automatic)
        self.tableView.endUpdates()
    }            
}

何时加载新对象的方法

var isMoreDataLoading = false
var loadingMoreView : InfiniteScrollActivityView?

/* Loads more feed while scrolling */
override func scrollViewDidScroll(_ scrollView: UIScrollView) {

    if (!isMoreDataLoading) { //is not loading more

        // Calculate the position of one screen length before the bottom of the tableview
        let scrollViewContentHeight = tableView.contentSize.height
        let scrollOffsetThreshold = scrollViewContentHeight - tableView.bounds.size.height

        //start loading more data after user went 4/5 of the way through the content
        if(scrollView.contentOffset.y > 4*scrollOffsetThreshold/5 && tableView.isDragging) {

            isMoreDataLoading = true //set loading data to true

            // Update position of loadingMoreView, and start loading indicator
            let frame = CGRect(x: 0, y: tableView.contentSize.height, width: tableView.bounds.size.width, height: InfiniteScrollActivityView.defaultHeight)
            loadingMoreView?.frame = frame
            loadingMoreView!.startAnimating()
            loadMoreFeed()

        }                
    }
}

Answer 1

对于何时加载新对象的方法，这是我的实现

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {    
  let lastSectionIndex = tableView.numberOfSections - 1
  let lastRowIndex = tableView.numberOfRows(inSection: lastSectionIndex) - 1
  if indexPath.section ==  lastSectionIndex && indexPath.row == lastRowIndex {
    // print("this is the last cell")

    if (!isMoreDataLoading) { //is not loading more
      // start loading indicator
      loadMoreFeed()

      // Update position of loadingMoreView, and 
      loadingMoreView?.frame = CGRect(x: 0, y: 0, width: tableView.bounds.size.width, height: InfiniteScrollActivityView.defaultHeight)
      loadingMoreView!.startAnimating()

       self.tableView.tableFooterView = loadingMoreView
       self.tableView.tableFooterView?.isHidden = false
    }
  }
}

为了更新 tableView 这是我的实现

private func updateTableView() {
  let rowsBefore = self.tableObjects.count
  loadMoreFeedInBackground() { queryObjects in
  for object in queryObjects! {
    self.tableObjects.append(object)
  }

  self.tableObjects.sort {
    $0.date!.compare($1.date!) == .orderedDescending 
  }

  let rowsAfter = self.tableObjects.count
  let indexes = rowsAfter - rowsBefore

  guard indexes > 0 else {
    self.isMoreDataLoading = false
    self.loadingMoreView!.stopAnimating()
    self.tableView.tableFooterView?.isHidden = true
    return
  }

  var indexPaths = [IndexPath]()
  for index in 0...(indexes - 1) {
    let indexPath = IndexPath(row: index + rowsBefore, section: 0)
    indexPaths.append(indexPath)
  }

  if tableView.contentOffset.y > tableView.estimatedRowHeight {
    let initialOffset = self.tableView.contentOffset

    tableView.beginUpdates()
    tableView.insertRows(at: indexPaths, with: .fade)
    tableView.setContentOffset(initialOffset, animated: false)
    tableView.endUpdates()

  } else {
    tableView.insertRows(at: indexPaths, with: .fade)
  }

  //refreshControl.endRefreshing()
}