最后一个tableview单元格使所有单元格扩展 - 迅速

Question

我正在创建一个UITableViewCell，用于在单击时展开单元格。基本上一切都有效，但是当我点击最后一个单元格时，我遇到了问题。发生这种情况时，所有单元格都会扩展到200（高度）。以下是我的代码。我很感谢社区在这个问题上的帮助。

var selectedIndexPath : NSIndexPath?

override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
  return 1
}

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
  return 4
}

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
  let cell = tableView.dequeueReusableCellWithIdentifier(cellID, forIndexPath: indexPath) as! Cell
  cell.titleLabel.text = "Test Title"
  return cell
}

override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
  let previousIndexPath = selectedIndexPath
  if indexPath == selectedIndexPath {
    selectedIndexPath = nil
  } else {
    selectedIndexPath = indexPath
  }

  var indexPaths : Array<NSIndexPath> = []
  if let previous = previousIndexPath {
    indexPaths += [previous]
  }
  if let current = selectedIndexPath {
    indexPaths += [current]
  }
  if indexPaths.count > 0 {
    tableView.reloadRowsAtIndexPaths(indexPaths, withRowAnimation: UITableViewRowAnimation.Automatic)
  }
}

override func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
  (cell as! Cell).watchFrameChanges()
}

override func tableView(tableView: UITableView, didEndDisplayingCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
  (cell as! Cell).ignoreFrameChanges()
}

override func viewWillDisappear(animated: Bool) {
  super.viewWillDisappear(animated)
  for cell in tableView.visibleCells as! [Cell] {
    cell.ignoreFrameChanges()
  }
}

override func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
  if indexPath == selectedIndexPath {
    return Cell.expandedHeight
  } else {
    return Cell.defaultHeight
  }
}

对于tableview ell类，代码为：

var isObserving = false;    
@IBOutlet weak var titleLabel: UILabel!
class var expandedHeight: CGFloat { get { return 200 } }
class var defaultHeight: CGFloat  { get { return 40  } }

func checkHeight() {
  titleLabel.hidden = (frame.size.height < Cell.expandedHeight)
}

func watchFrameChanges() {
  if !isObserving {
    addObserver(self, forKeyPath: "frame", options: [NSKeyValueObservingOptions.New, NSKeyValueObservingOptions.Initial], context: nil)
    isObserving = true;
  }
}

func ignoreFrameChanges() {
  if isObserving {
    removeObserver(self, forKeyPath: "frame")
    isObserving = false;
  }
}

override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
  if keyPath == "frame" {
    checkHeight()
  }
}