使用UITableViewAutomaticDimension更新UITableViewCell后的生涩滚动

Question

我正在构建一个具有用户提交帖子的Feed视图的应用.此视图具有UITableView自定义UITableViewCell实现.在这个单元格中,我有另一个UITableView用于显示注释.要点是这样的:

Feed TableView
  PostCell
    Comments (TableView)
      CommentCell
  PostCell
    Comments (TableView)
      CommentCell
      CommentCell
      CommentCell
      CommentCell
      CommentCell

初始订阅源将下载3条评论进行预览,但如果有更多评论,或者用户添加或删除评论,我想PostCell通过添加或删除CommentCells评论表内部来更新Feed表视图内的位置的PostCell.我目前正在使用以下帮助程序来完成此任务:

// (PostCell.swift) Handle showing/hiding comments
func animateAddOrDeleteComments(startRow: Int, endRow: Int, operation: CellOperation) {
  let table = self.superview?.superview as UITableView

  // "table" is outer feed table
  // self is the PostCell that is updating it's comments
  // self.comments is UITableView for displaying comments inside of the PostCell
  table.beginUpdates()
  self.comments.beginUpdates()

  // This function handles inserting/removing/reloading a range of comments
  // so we build out an array of index paths for each row that needs updating
  var indexPaths = [NSIndexPath]()
  for var index = startRow; index <= endRow; index++ {
    indexPaths.append(NSIndexPath(forRow: index, inSection: 0))
  }

  switch operation {
  case .INSERT:
    self.comments.insertRowsAtIndexPaths(indexPaths, withRowAnimation: UITableViewRowAnimation.None)
  case .DELETE:
    self.comments.deleteRowsAtIndexPaths(indexPaths, withRowAnimation: UITableViewRowAnimation.None)
  case .RELOAD:
    self.comments.reloadRowsAtIndexPaths(indexPaths, withRowAnimation: UITableViewRowAnimation.None)
  }

  self.comments.endUpdates()
  table.endUpdates()

  // trigger a call to updateConstraints so that we can update the height constraint 
  // of the comments table to fit all of the comments
  self.setNeedsUpdateConstraints()
}

override func updateConstraints() {
  super.updateConstraints()
  self.commentsHeight.constant = self.comments.sizeThatFits(UILayoutFittingCompressedSize).height
}

这样就完成了更新.帖子已更新到位,并PostCell在预期内添加或删除了评论.我PostCells在feed表中使用自动调整大小.PostCell扩展的注释表显示所有注释,但动画有点不稳定,并且在进行单元格更新动画时,表格会向上和向下滚动十几个像素.

调整大小时的跳跃有点烦人,但后来我的主要问题出现了.现在,如果我在Feed中向下滚动,滚动就像以前一样平滑,但是如果我在单元格上方向上滚动,我只是在添加注释后调整大小,Feed会在到达Feed的顶部之前向后跳几次.我iOS8为Feed 设置了自动调整大小的单元格,如下所示:

// (FeedController.swift)
// tableView is the feed table containing PostCells
self.tableView.rowHeight = UITableViewAutomaticDimension
self.tableView.estimatedRowHeight = 560

如果我删除了estimatedRowHeight,只要单元格高度发生变化,表格就会滚动到顶部.我现在感觉很困惑,作为一个新的iOS开发人员,可以使用你可能有的任何提示.

Answer 1

这是我发现解决此类问题的最佳解决方案(滚动问题+ reloadRows + iOS 8 UITableViewAutomaticDimension);

它包括将每个高度保持在字典中并更新它们(在字典中),因为tableView将显示单元格.

然后,您将在- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath方法中返回已保存的高度.

你应该实现这样的事情:

Objective-C的

- (void)viewDidLoad {
    [super viewDidLoad];

    self.heightAtIndexPath = [NSMutableDictionary new];
    self.tableView.rowHeight = UITableViewAutomaticDimension;
}

- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSNumber *height = [self.heightAtIndexPath objectForKey:indexPath];
    if(height) {
        return height.floatValue;
    } else {
        return UITableViewAutomaticDimension;
    }
}

- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
    NSNumber *height = @(cell.frame.size.height);
    [self.heightAtIndexPath setObject:height forKey:indexPath];
}

斯威夫特3

@IBOutlet var tableView : UITableView?
var heightAtIndexPath = NSMutableDictionary()

override func viewDidLoad() {
    super.viewDidLoad()

    tableView?.rowHeight = UITableViewAutomaticDimension
}

func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
    if let height = heightAtIndexPath.object(forKey: indexPath) as? NSNumber {
        return CGFloat(height.floatValue)
    } else {
        return UITableViewAutomaticDimension
    }
}

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    let height = NSNumber(value: Float(cell.frame.size.height))
    heightAtIndexPath.setObject(height, forKey: indexPath as NSCopying)
}

Answer 2

我们遇到了同样的问题.它来自对单元格高度的错误估计,导致SDK强制导致较高的高度,这会导致向上滚动时单元格的跳跃.根据您构建单元的方式,解决此问题的最佳方法是实现该UITableViewDelegate方法- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath

只要您的估计非常接近细胞高度的实际值,这几乎可以消除跳跃和急动.这是我们实现它的方式,你将得到逻辑:

- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath {
    // This method will get your cell identifier based on your data
    NSString *cellType = [self reuseIdentifierForIndexPath:indexPath];

    if ([cellType isEqualToString:kFirstCellIdentifier])
        return kFirstCellHeight;
    else if ([cellType isEqualToString:kSecondCellIdentifier])
        return kSecondCellHeight;
    else if ([cellType isEqualToString:kThirdCellIdentifier])
        return kThirdCellHeight;
    else {
        return UITableViewAutomaticDimension;
    }
}

添加了Swift 2支持

func tableView(tableView: UITableView, estimatedHeightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
    // This method will get your cell identifier based on your data
    let cellType = reuseIdentifierForIndexPath(indexPath)

    if cellType == kFirstCellIdentifier 
        return kFirstCellHeight
    else if cellType == kSecondCellIdentifier
        return kSecondCellHeight
    else if cellType == kThirdCellIdentifier
        return kThirdCellHeight
    else
        return UITableViewAutomaticDimension  
}

Answer 3

dosdos的答案在Swift 2中为我工作

宣布伊娃

var heightAtIndexPath = NSMutableDictionary()

在func viewDidLoad()中

func viewDidLoad() {
  .... your code
  self.tableView.rowHeight = UITableViewAutomaticDimension
}

然后添加以下两种方法:

override func tableView(tableView: UITableView, estimatedHeightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
   let height = self.heightAtIndexPath.objectForKey(indexPath)
   if ((height) != nil) {
     return CGFloat(height!.floatValue)
   } else {
    return UITableViewAutomaticDimension
   }
 }

override func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
  let height = cell.frame.size.height
  self.heightAtIndexPath.setObject(height, forKey: indexPath)
}

SWIFT 3:

var heightAtIndexPath = [IndexPath: CGFloat]()

func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
    return self.heightAtIndexPath[indexPath] ?? UITableViewAutomaticDimension
}

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    self.heightAtIndexPath[indexPath] = cell.frame.size.height
}